SOME BASIC PROPERTBES G? 'FHE COFFEE FRUIT AND CQFFEE BEANS The“: for FM Degree 0% M. S. MICHISAN STATE UNIVERSETY Adoifo Eschenwaid 1959 THESlS WWHHHUHWHO“ HHLN \H W HM H7“2 HHH I _ 312930 III} R~1R Y a DI 1315‘: MC 14!? U1 cmity I l PLACE ll HEI’UM IOanmwoflnchockoummnoord. TOAVOIDFINESMumonorbdondaoduo. DATE DUE DATE DUE DATE DUE :1: | IDW L__J-L__J :JI—J: m MSURMWMWOWIW W1 II 30MB BASIC PROPERTIES OF THE COFFEE FRUIT AND COFFEE BEANS By ADOLPO ESCHENWALD AH ABSTRACT SUBMITTED TO THE COLLEGE or AGRICULTURE or MICHIGAN STATE UNIVERSITY or AGRICULTURE AND APPLIED SCIENCE IN PARTIAL FULFILLMENT or TEE REQUIREEEETS EUR TEE DEGREE or EASTER or SCIEECE DEPARTMENT OF AGRICULTURAL ENGINEERING 1959 APPROVED BY WM 994.11% 2 {7:7 ABSTRACT The investigation is primarily concerned with the experinental determination of basic engineering properties of the coffee fruit and perch-cut coffee beans. Little work has been done on this subject. The scant and inconplete infornation available is only on a linited phase of the prohlen, nannly drying. A practical leans of shipping fresh coffee fruits fron Puerto Rico toiuichigan State University was worked out so that the green and ripe fruits arrived in perfect condition. Best tauperatures and relative hunidities for storage in a fresh condition were also deternined. The equip-ant and the working procedure was prepared ahead of tfine and tested. Shipping schedules were planned carefully. Data are presented on: 1. Coefficient of friction and angle of repose of coffee fruit and coffee beans 2. Initial rebounding or resiliency studies for coffee fruits 3. Specific gravity and bulk density 4. Air flotation and conveying velocities 5. Air :1... relationship 6. Exposed drying rates 7. Bqnilibrim noisture contents for perch-eat coffee and a, Prelininary studies on electronic sorting of green and ripe fruits. SOB BASIC PROPERTIES OF THE COFFEE FRUIT AND COFFEE BEANS By ADOLPO ESCEENUALD A THESIS SUBMITTED TO TEE COLLEGE OF AGRICULTURE OF MICHIGAN STATE WIVERSITY OF AGRICULTURE AND APPLIED SCIENCE IN PAHIAL FULFILLMENT 0!’ m REQUIREMENTS FOR THE DEGREE 0? MASTER OF SCIENCE DEPAMNT OF AGRICULTURAL ENGINEERING 1959 APPROVED ET (M A}. W hall/fr! ACKNOWLEDGEIENTS.... LISTOFPIGURES sees LISTOPTABLES..... INTRODUCTION...... OBJECTIVE. assess HATERIALSIBED..... REVIEWOPLITEEATURE.. PROCEDURE.. ..... TABLEOPCONTENTS Coefficient of friction and angle OfrCPOCstessss R93111mcys O O O D O O O O O O 0 O O O O O O O 0 O O O 0 Specific gravity and bulk density . . . . . . . . . . . . Air flotation and air conveying velocities. . . . . . . . Air Flow relationships. . . . . . Exposed drying . . . . Equilibrium moisture Electronic sorting . RESULTS AND DISCUSSION . CONCLUSIONS . . . s s s . contents . . RECMENDATIONS FOR FURTHER STUDIES. . REFERENCES ........ Page 12 13 16 29 29 32 33 36 37 4O 42 78 81 83 85 ACKNWNTS The author wishes to express his appreciation to Dr. Carl W. Hall for the valuable guidance and assistance. He sincerely thanks Dr. Frederick H. Buelow of the Agricultural Engineering Departnent and lir. Francis 1.. O'Rourke of the Horticulture Departnent for their very nice assistance and cooperation. Thankful acknowledpent is also due to the personnel of the Agricultural Engineering Research laboratory for their valuable help. The author wishes. to express his grateful appreciation to the Puerto Rico Agricultural lxperinent Station for their cooperation and also to llr. Fernando Serra fron Wagner, Puerto Rico who gathered and shipped selected coffee fruit s-ples. Appreciation is extended to the Sortex Conpany of Anerica, Lovell, Hichigan for their cooperation in electronic sorting studies. The author also likes to record his acknowledgnsnts to his wife and children whose patience and understanding helped greatly to neke possible the coupletion of this Thesis. LIST OF FIGURES Pig. COFFEEPROCESSINGFIDHCHART........ ...... . l TILTING TABLE USED FOR COEFFICIENT OF FRICTION DammMIms I O O O I O O O C O O I O O O O O O O O O O 2 EQUIPMENT USED FOR RESILIENCY STUDIES. . . . . . . . . . . 3 EQUIPMENT USED FOR AIR FLOTATION VELOCITY . . ...... 4 EQUIPMENT USED FOR AIR FLOW RELATIONSHIPS . . . . . . . . 5 EQUIPMENT USED FOR PARCEHENT COFFEE DRYING . . . . . . . . 6 AVERAGE VELOCITIES AND AIR VOLUME FOR CONVEYING MARRIAL . 7 PRESSURE DROP TEROIBE ORIFICES . . . . . . . . . . . . . . 8 COEFFICIENT OF DISCEAME FOR A ONE-HALF VENA-CONTRACTA ORIFICEINATHREEINCHPIPE............... 9 RESISTANCE OF GREEN COFFEE FRUIT TO AIR FLOW . . . . . . . 10 RESISTANCE OF RIPE COFFEE FRUIT TO AIR FLOW . . . . . . . 11 RESISTANCE OF PARCEHEN‘I‘ COFFEE TO AIR FLOW (55.6% to 53.52 and 52 to 49.1% v.3. MOISTURE CONTENT) . . 12 REsIsTAECE or PM COFFEE To AIR now (45.4% to 45.07: and 13.3 to 11.77. v.3. MOISTURE COMEN'I‘) . 13 EXPOSEDDRYINGFORPARCEMENTCOFFEE.......—... . 14 EXPOSED DRYING RAES FOR PARCEMENT COFFEE (0 to 50 HOURS) . 15 EXPOSED DRYIM RARS FOR PARCBNENT COFFEE (0 to 40 MINUTES) 16 COFFEE FRUITS AND BEANS AT DIFFERENT STAGES OF PROCESSING 17 CROSS SECTION OF A MATURE COFFEE FRUIT . . . . . . . . '. . 18 EQUILIBle MOISTURE CONTENT OF PARleENT COFFEE . . . . . 19 Page 11 31 31 35 35 38 SO 53 54 55 57 59 '61 7o 71 72 73 76 77 LIST OF TABLES Table Page WORLDGREENCOFFEEPRODUCTION....... ...... l 9 WORLD GREEN COFFEE woman PRODm'l‘ION . . . . . . . 2 10 COEFFICIENT 0F FRICTION OF COFFEE FRUIT AND COFFEE BEANS 3 44 SPECIFIC GRAVITY AND DENSITY OF GREEN AND RIPE COFFEE FRUI'B 4 47 BULKDENSITTOFCOFFEE FRUITSANDCOFFEEPULP . . . . . . 5 47 AVERAGE AIR VELOCITIES FOR CONVEYING COFFEE FRUITS, PM m M C O O O O D O C C O C O O I O O I C O O O 6 so RESISTAME OFG‘I COFFEE FRUITSTOAIRFIDU . . . . . 7 52 RESISTANCEOFRIPECOFFEEFRUITSIOAIRFLOU. ..... 8 56 RESISTANE OF “ASKED NET PAEEIENT COFFEE TO AIR FLOW (55.“ to 530% ".3. mmm CW) 0 C O O D C O O O 9 56 RES ISTANGE 0F NASRED PARCEMENT COFFEE BEANS TO AIR FLOW (52.01 to 49.1% ".8. WISTURE CONTENT) . . . . . . . . . 10 58 RESISTAIBE 0F UASEED PAKIl-MENT COFFEE BEANS TO AIR FLOW (45.41 to 45.07. W.B. mISTURE C(NTENT) . . . . . . . . . 11 58 RESISTANCE OF DRIED PAEUHENT COFFEE BEANS TO AIR FLOW (13sn to llsn “.3. mum CM“) 0 s s s e a s e s 12 60 EXPOSEDDumGRATEsPORcomEEEANsAT85°P...... 13 ‘64 EXPOSED DRYING RATES FOR COFFEE BEANS AT 100° 7. . . . . 14 6s EXPOEED DRYING RATES FOR com: BEANS AT 120° P. . . . . Is 66 EXPOSED DRYING RATES FOR come BEANS AT 140° r. . . . . 16 67 EXPOGEDDRTING Russ PoRCOTrEEEEANsATI60°P. . . . . 17 6s EXPOEED DRYING RATES FOR COFFEE DEANS AT 180° P. . . . . 18 69 804E BASIC PROPEHIES OF THE COFFEE FRUIT AND COFFEE BEAN INTRODUCTION Coffee is a very inportant crop in the world nsrket. The econony of several nations in North America, South Anerica, Africa and Asia depend to a great extent on the production, harvesting, processing and nsrketing of coffee. (World SI-aries, 1958) (Guiscafre , 1953). Over 90 percent of the American fanilies serve coffee and lore Anerican fanilies use coffee regularly than any other table served iten except sugar and salt. Per capita consunption has increased trenendously in the United States of Ansrica. (Horn, 1954). .A great anount of research work has been done on varieties and cultural practices. Very little basic infornntion is available on processing. The regular routine of hundreds of years is being followed in this inportant phase of the preparation of the crop for the narket. Sane of the sparsely available infornation is contradictory and is based on experiences or observations with little or no research data. This condition is aggravated by the fact that coffee is a product that requires considerable handling and processing on the fern before it is ready for the nsrket. The very poor keeping qualities of the unprocessed product and the susceptibility to rapid deterioration in quality nakes the inrovelnent of processing very challenging. (Eschenwnld, 1957) (Vivaldi, 1957). It is a well known and accepted principle that a coffee tree, of the right variety, produces top quality coffee. It is also very well known and generally accepted that very little if anything can be done to improve this already present quality. 0n the other hand quality can be rapidly and pernanently inpaired without affecting the appearance of the processed product. (Baron Cute, and Fukvnaga, 1956) (Howard, 1954) (Lockhart, 1956). For years, coffee production and processing has been living in the past and has become static in nany of its phases. The picking, handling, sorting and processing of the crop are good examples. Coffee needs scientific research and a logical start is uncovering basic, prelininsry data that night seTVe as basis for future develop~ nents. Toward these goals has this work been directed. A brief su-nsry follows for those who are not faniliar with the coffee production. Coffee is produced in the tropical regions of the world under a great variety of conditions ranging fron very intensive to very extensive fans of cultivation. It is grown at elevations varying fron sea level to as high as 5,000 to 7,000 feet. The lower elevation orchards are usually in the higher latitudes (22° to 25°). The optinun temperatures seems to be a nininna of 60° F. and a naxinun of about 80° F. with very ‘little fluctuations below or above these linits. (Debecca, 1958) (Reynan, 1955). The general botanical classification of coffee is still con- fusing when dealing with varieties and species. A general accepted classification follows.‘ (Core, 1955) (Jordan, 1957). Kingdon - Vegetable Sub-kingdat - Angiospgmg Class - Dicotyledoneae Sub-class - sgetalae Order - m Family - Rubiaceae Genus - Coffee Sub-genus - Eucoffeae Specie - m, liberica, canephora, robusta, and many others Under average conditions it takes from four to five years, fron the preparation of the seed bed, to the time the trees start bearing fruit. Full production is obtained after the sixth year. The coffee fruit has been called a cherry or a berry. It is a drupe, nornally containing two seeds. Occasionally there occurs three or nore seeds as tri-celled or pluri-celled ovaries or through false polyembryony. On the other extrene, a one-seeded fruit is con-Ion due to the abortion of an-ovule. The fruit, originally green, turns to a yellowish green and finally to a cherry red color on ripening. It is formed by the following layers free the outside to the center: Epicarp or pulp, nesocarp or nucilage, espernodern, and embryo. Sone countries store or export their coffee as parchnent coffee and sone as hulled coffee. llulled coffee, when the parchnent has been removed, is known as green coffee. Parchment coffee has a longer keeping quality than green coffee. For general calculations of quantity and for statistical ‘data all coffee, either parchment or green, is expressed as green coffee. The fruit is picked by hand when completely ripe. All efforts, so far, to nechanize the picking has failed due to the flowering and fruiting habits. Sone progress hasbeen attained in the efficiency of hand pickers by the application of time and notion studies where the basic movements (Therblings) have been analyzed and simplified (Eschenwald, 1957) . As soon after harvest as feasible, the processing must be started and should not be stopped until the seeds are dried to about 12 to 13 percent moisture content, dry basis. There are two general ways of processing coffee according to the. procedure followed. These are known as dry processing and wet processing. Dry processing is practiced only in places where water is scarce or in backward areas of extensive cultivation where quality is not considered. Wet processing is more costly and elaborate. It requires more facilities, equipment, machinery and know-how. The co-odity obtained is of far superior quality. This is the method followed in the more intensive and specialized areas of production. Figure 1 shows a wet processing flow chart. The basic steps in the wet process method are as follows: 1. Pulping - removal of the epicarp. This is done very efficiently by machines of various design. (Daron Goto and Fukunaga, 1956) (Eschenwald, 1957) (Gutierrez and Alvarez, 1957). 2. Denucilaging - removal of the mesocarp. The mesocarp, which consists mainly of pectines is removed by three generally used methods which can be classified as fermentation, chemical and mechanical (Alvarez, 1956) (Blasingame and Eschenwald, 1954) (Carbonell and Vilanoua, 1952) (Eschenwald, 1957) (Hansen, 1952). 3. Washing - once the mucilage is removed, the coffee beans are thoroughly rinsed in clean water. 4. _D_I_'z_i_n_g - the drying process must be started inediately or the beans must be kept for short periods of time under circulating water. Drying is done in the sun or by using heated air dryers. The use of indirectly heated air dryers is becoming more and more a part of coffee production. During all these stages in the process- ing the fruits and the beans must be handled several times before the product is ready for the market. Basic engineering data are essential for more efficient handling and processing of the coffee crop. A summary of the world coffee production and export follows. (World summaries, foreign crops and markets, U.S.D.A., 1958). Table 1. World green coffee production, 1000 Bags 11) Percent Continent Year of'lunl ngznt e Projdi , n 111-33. 1954-55 1955-56 1956-57 1957-58 1958-59 1959 1954 Estilmnd 1599 North America b) 7,489 7,823 7,750 8,575 8,525 14.5 14 South America c) 26,022 31,575 26,040 32,780 37,980 65.0 46 Africa d) 7,112 8,749 8,775 8,600 9,560 16.3 34 Asia&0ceaniae) 1,565 2,201 2,625 2,590 2,590 4.2 59 Total World Production 42,188 50,348 45,190 52,545 58,655 11) 132.276 pounds each b) Major producers - Costa Rica, Cuba, Dominican Republic, El Salvador, Guatemala,Haiti, Honduras, Mexico and Nicaragua. Minor producers - Hawaii, Guadalupe, Jamaica, Panama, Puerto Rico and Trinidad. c) Major producers - Brazil, Columbia, Ecuador, Peru and Venezuela. Minor producers - Bolivia, British Guiana, Paraguay and Surinam. d) Major producers - Angola, Belgian Congo, Cameron, Ethiopia, French West Africa, Kenya, Madagascar, Tanganyika, Togo and Ugnada Minor producers - Cape Verde, Ghana, French Equatorial Africa, . Liberia, Nigeria, Sao Tone, Sierra Leone and Spanish Guinea. e) Major producers - India, Indonesia and Yemen. Minor producers - New Caledonia, New Hebrides. North Borneo Philippines, Portugese Timor and Vietnam. Table 2. World green coffee exportable production 1000 Bags a) 5315859361. Continent Year 1954-55 1955-56 1956-57 1957-58 1958-59 End-Dad North America 1)) 5,437 5,779 5,830 6,580 6,615 South America c) 20,984 28,286 18,475 28,025 33,745 Africa d) 6,839 8,395 8,330 8,140 9,095 Asia Smmia Q 662 1,157 1,737 1,635 1,590 Total World Exportable Pro- duction 33,922 43,617 34,372 44,380 51,045 87 a) 132.276 pounds each h) Major producers - Costa Rica, Cuba, Dominican Republic, El Salvador, Guatemala, Haiti, Honduras, Mexico and Nicaragua. Minor producers - Hawaii, Guadalupe, Jamaica, Panama, Puerto Rico and Trinidad. c) Major producers - Brazil, Colusbia, Ecuador, Peru and Venezuela. Minor producers - Bolivia, British Guiana, Paraguay and Surinam. d) Major producers - Angola, Belgian Congo, Cameroum, Ethiopia, - French West Africa, Kenya, Madagascar, Tanganyika, Togo and Ugnada. Minor producers - Cape Verde, Ghana, French Equatorial Africa, Liberia, Nigeria, Sao Tome, Sierra Leone and Spanish Guinea. e) Major producers - India, Indonesia and Yemen. Minor producers - New Caledonia, New Hebrides, North Borneo Philippines, Portugese Timor and Vietnam. The United States is the major coffee importer with 'a total of 2,761,190,000 pounds imported in 1957 which has a cash value of 1,375,736,000 dollars. 10 coffee from farm WWW ’7; ”7r rim / ” I/r/l/Inr rI/////f//// washer to remove fresh and foreign maferial , “5‘99; \‘ ‘x\\\{{\\: FIG.| I / 7 7 7 / /‘ ('1’ / I/ /sorlinq (~cenfrifuge Sholding bin for ripe fruits indirect healed air rotary drum dryer “ :rt;i1":;£j‘j_r"“: ' ‘ <6 1. l l LIiw ' ; /.L"_I. I“_LH.I _L.- , l ,1, L “1; fi’7//}// //7/// // cooling bin ///////W\\\Lwashed coffee and wafer // loading plalforrn //////////////////// COFFEE PROCESSING FLOW CHART 11 OBJECTIVE The main objective was to determine some basic properties of the coffee fruit and coffee beans. The following were evaluated: 1. 2. Coefficients of friction and angle of repose. Rebounding characteristics of green and ripe fruit. Specific gravity and bulk density. Air flotation and conveying velocities. Resistance to air flow. Drying rates. Equilibriun nois ture contents. Electronic sorting. 12 ‘HAIERIAL USED The coffee fruits (coffee arabica, forms native) used in this study were shipped from.Puerto Rico by air freight during 1958 coffee harvesting season. Harvesting starts at the beginning of June in the lower, warmer sections and lasts till November in the higher and cooler parts. Getting the fruits in good condition was one of the most difficult and sometimes discouraging part of the work due to the human element involved. Unlimited cooperation, precise timing, and desire to succeed were essential but not always present and some ' shipments were a total loss. The complete lack of information as to the storage and transportation of the coffee fruit was also a great handicap to the project. Some small test shipments were sent upon request, by personal friends in the western part of the island. Others were sent by the Puerto Rico Experiment Station, from their Coffee Sub-station located in the central mountainous region. These shipments, ‘ 5 in'total, amounted to 30 pounds of green and 30 pounds of ripe fruits. Packed in different ways, but not refrigerated, all the ripe fruits in everyone of the shipments suffered some discoloration in the short period required for air transportation. The seeds or beans, however, were not affected since they are very well protected by all the outer layers of the fruit. These were used for some of the preliminary determinations. In order to get a fresh fruit with a natural color a survey of previous work along this line was conducted. Two methods of approach were followed namely: literature and contacts with specialists. The results were negative in both cases since no basic work has been done in coffee fruit storage and transportation. The 13 use of information available for other crops serves as a guide to plan for a carefully well-timed shipment where a combination of cooling, aeriation, and carbon dioxide atmosphere were to be provided (Goets, 1955) (Guillow, 1958) (Pentzer, and Heinze, 1954). A special box was prepared by the Agricultural Engineering personnel at the College of Agriculture, University of Puerto Rico for a trial shipment. Twanty pounds of green fruits and twenty pounds of ripe fruits, re- cently picked, were placed loosely in onion bags. These, in turn, were placed in separate, partially insulated, compartments of the wooden box and dry ice was placed in the center. The package was sent inediately by air freight and picked up at the Lansing airport two days after shipment. The correct timing in the picking, packaging and sending enabled receiving fresh fruit in very good condition and with all their natural color. Part of the fruits were taken inediately to the Electronic Sorting Company at Lowell, Michigan. Previous arrangements had been made to run some electronic . sorting tests of green and ripe fruit. The rest of the fruit was stored at 50° F. and approximately 90 to 95% relative humidity. The general principle that tropical and sub-tropical fruits and vegetables require a high storage temperature and a very high relative humidity was followed (Biale, 1950) (Rose, e_t_. _a_l_._., 1954) (Ulrich, 1958) (U.S.D.A, 1953). The equipment and materials needed for the determin- ations, where fresh fruit was required, has been prepared and tested before-hand. In this way the tests were conducted in the minimum time and when the fruits were in the best condition of freshness. For the rest of the study, periodic samples were taken from storage, processed and used. Under these conditions the fruits, which normally are very perishable, lasted for 6 weeks in good condition. 14 Color pictures taken after 30 days storage show the fruits are still fresh and of a natural color (Fig. 17). At the end of six weeks the ripe fruits start to soften and develop mold and the green ones were turning yellow and ripening slowly. The beans inside the fruit, however, were normal in appearance. 15 REVIEW 0? LITERATURE The review of literature is presented for each of the aspects covered in the study and is therefore composed of eight parts. No work has been reported on coffee or any of the specific fields covered here so the review of literature is based on similar work done for other crops or work done on coffee in related fields. 1. Coefficient of friction and anfle of repose. Wifred (1898) reported results of studies on angle of repose, coefficient of friction and bulk densities for wheat, barley, oats, corn, beans, peas, tares, and flax seed on rough boards, smooth boards, iron and concrete. Jamieson (1905) coefficients of friction between wheat and various materials of construction were reported. Ketchum (1911) reported data compiled from experiments conducted by V. Pleissner on the coefficient of friction for wheat and rye and bin wall material. The ratio of the lateral to the vertical pressure exerted by the grain is also discussed as a function of the bin wall material. Values reported for similar materials and grain vary some from the values reported by Jamieson (1905) probably due to variety and moisture content. Kramer (1944) reported the angle of repose and coefficient of friction for rice and several construction materials. The moisture content of the product was considered. 16 Hints and Schinke (1952) determined the coefficient of sliding friction for chopped corn and alfalfa on steel at sliding velocities from O to 6000 fpm. Results show that the sliding coefficient of friction above 1000 fpm did not vary mach from 0.5. At velocities below 1000 fpm the results vary widely. Richter (1954) conducted laboratory tests to determine friction coefficients for chopped hay, straw and silage on galvanized steel. Static coefficients were determined by a weight system in which the weidlt required to start motion gave a measurement of friction force. Sliding coefficients were determined by sliding a surface under the product and recording the pull exerted at different velocities on a spring balance. Polishing of the steel surface reduced the coefficient of dry materials but had a lesser effect on the coefficient for moist material. There was a distinct tendency toward higher static coefficients for moist materials at the lower unit pressures. There were only small effects on the sliding coefficients of any nterial as a result» of varying sliding velocities or unit pressures. Results are su-Iarised as follows: Chopped hay and straw Range Recommended valves Static coefficient 0.17 - 0.42 0.35 Sliding coefficient 0.28 — 0.78 0.30 Silages Static coefficient 0.52 - 0.82 0.80 Sliding coefficient 0.57 - 0.78 0.70 17 Resiliency or rebounding of coffee fruit. There is no literature available along this line for any crop. The reason seems to be that any rough handling will seriously damage the product. There is the possibility that this is not the case with coffee fruits since the outer layers protect very well the bean and the outer layers are removed in processing. Specific Jr_avity_and bulk density; Zink (1935) points out that the specific gravity of a product is expressed as the ratio of mass of the body to the mass of an equal volt-e of water at 4° c. Work on specific gravity and air space in grain and seeds were performed by the use of specific gravity bottle principle. Mercury was used as a fluid. Air entrnped in the crevices and brush of some seeds gave an error estimated as 0.1 difference in specific gravity . Pflug 55.. $1.. , (1955) designed, constructedand operated at M.S.U. a specific gravity separator for potatoes. It consists of a separating tank, a reservoir tank, two con- veyors and a circulating pimp. Sodium chloride brine was used as the separating medium. The brine specific gravity was calibrated at 1.080. All potatoes that had 1.080 or higher, specific gravity sink to the bottom where they were removed by a conveyor. All potatoes that had less than 1.080 specific gravity value floated and were picked out by a second conveyor located at a higher level. In the fraction 18 separated as floaters 15 to 20 percent were in the specific gravity range of 1.080 to 1.085 with the remainders below 10080. Air flotation and conveying velocities. Sturtevant Division of Westinghouse Corporation (1946) developed air velocities and air volt-e curves for conveying material. The weight used is not the true density of the material but the average bulk weight of a cubic foot of the material in the condition in which it is to be conveyed. This work was reprinted in the Agricultural Engineering Yearbook, 1958 . United States Department of Agriculture, Grain Storage Laboratories (n.d.), worked out air velocities required to cause loose grain to move along the bottom of ducts. Madison (1949) published some generally used conveying air vel- ocities. The conveying velocity being directly related with the bulk density of the product. He reported that it is easier to convey material in a vertical pipe than in a horizontal one, in that lower velocities may be used to satisfactorily float the -terial. In a horizontal pipe too low a velocity allows a separation of the material from the air stren. Rice (1958) found that the particles with dimensions approach- ing sphere or cubes required the greatest velocity for con- veying. Air flow relationships . 19 Henderson (1943) determined and evaluated the air flow re- lationships for shelled corn. Information was needed for the design of natural and mechanical ventilating and drying ' systems. Results of the test were mathematically expressed and the fund-ental formula for clean shelled corn developed as follows: Q =RP° whereQ IIcfmpersquare foot K a function of depth of grain c slope of the curve P pressure drop in inches of water Shedd (1945) conducted some work on the resistance of ear corn to air flow. Pull size bins were used since ear corn tend to bridge and the smaller the bin the less the compaction. Air flow rates of 10, 20, 30, 40,50, 60 and 70 cfm per square foot were used. Air flow measurements were done with a pitot tube located in the pipe between the fan and the bin. Data which were plotted on logaritl-ic scale with air flow, Q, versus static pressure, P, resulted in a straight line. A formula of Q 8 0" represents the air f1ow--static pressure relationship. Shedd (1951) reports data on the resistance of grain to air flow. The air was supplied by an entirely different mechanism than the one used so far. An inverted ball over a reservoid full of water was used and as the bell was pushed up or down air circulates through the grain in either direction. He found that when drawing air through the grain the minus 20 static pressure was slightly less than the positive static pressure found when forcing air through. The condition of packing, moisture contents and foreign material caused more variations in air flow than had been expected. He observed that in a batch drying operation, a favorable factor would be that the grain shrinks first at the bottom of the bin as it dries. This would cause the grain to be less densely packed after drying has started than at the beginning of the drying operation. Shedd (1953) stated that if the air flow-static pressure relationship was ploted in logarithmic paper come out as a straight line this relationship could be expressed by the already mentioned formula. Q I aP° where Q 5 air flow in cfm per square foot; P 8 pressure drop per foot depth of grain in inches of water a and c ' constants for any one lot and condition of grain. He also found that the general slope of the curve is greater for fine material than for a coarse one. If the material is fine the formla will fit the curve for only a narrow range of rates of air flow. Pine material produce a convex curve when the air flow is plotted versus the pressure drop. Hall (1955) presents a method for rapidly and accurately determining air-flow values in grain drying structures of non-rectangular cross section. Plotting in logaritbic scale the air-flow in cfm per square foot against the depth of grain in inches for various static pressures a straight line relation- 21 ship was obtained. These ieopreuure lines are very easily used to find the resistance of a certain air flow for any depth of the grain. mesed drying rates. Madison (1949) published a table of drying temperatures and drying time for different crops. Temperatures fra 140° F. to 150° F. for 40 hours are reco-ended for coffee drying. Lopez (1952) found that high drying temperatures, frm 60° to 105° C. (140° to 221° F.) cause a corresponding increase deterioration in quality until completely ruined from the aroma and flavor point of view. He also reported that the higher the initial water content of the product the lower the initial drying temperature to use. The heating of the water in the product increases its ability to dissolve organic compounds. These compounds move with the water to the outer layers of the been where the heat volatilises all the low boiling point aromatic constituents resulting in a very low quality product. As the bean dries out this solvent action is less pronounced and higher than starting temperatures can be used safely. Llewelyn (1955) states that drying of coffee should be done in three stages, namely: Stage 1 - fully wet (approx. 541 w.b. moisture content) to skin dry (431) using sun drying and thin layers of grain until such time as specially-designed dryers become available. 22 Stage 2 - skin dry to black stage (20-251) using bed or rotary dryers of conventional design. Stage 3 - black stage to final stage (about 111 w.b. moisture content) using ventilated silos. Ives (1955) reports studies conducted in Turrialba, Costa Rica since 1949 trying to find a method of drying coffee without 1 processing. no practical results have been attained due to the stale, vinegar like flavor of the final product. In 1952 the studies were modified. A fast means of drying processed coffee was then the main goal. When a temperature of 180° 1'. was attempted for fast drying the coffee beans. show a very marked bleaching which makes thn unsuitable for the market. When the initial drying is done at low temperatures higher final drying temperatures could be used safely. As pointed out by Lopez (1952) fast drying with high temperatures, independent of previous processing, always produce low quality coffee. Hall (1956) stated that the exposed drying rate of a product can be used for determining the effect of temperature and air flow on drying. Data on drying sugar beet seeds in single layers and in four inch layers are presented. McCloy (1956-57) reports that the experiments started by Llewelyn, (1955) were continued in an effort to find a mechanical means of drying arabic parchment coffee, which cause little or no loss of quality. Fifty-eight field scale experiments on bed driers and sixteen on radial flow and 23 flow-ventilated silos have shown that the suggested method by Llewelyn avoids the severe damage known to be caused by simple single-stage drying in about 24 hours, but may cause overall damage decreasing the coffee by one market class and thus the value. The damage occurs principally during Stage 2 with coffee which has first been skin-dried in the sun and then mechanically dried in conventional dryers in a 24-hour cycle with an air-inlet temperature of 120° F. Damage is somewhat more pronounced if fully wet coffee is put into the dryer. The Stage 2 process has been extended to a 48-hour cycle using.temperatures of 100° F., but damage has not been eliminated. Two practicable methods for i-ediate use which should not cause any'mnre dmnage to quality than would occur with sun-drying under difficult conditions are recommended as follows: 1. Sun-dry to the black stage and finish-dry in a conventional dryer using a temperature around 100-1200 2. in a 24 hour cycle. 2. Sun-dry to the skin-dry stage and.umchine-dry at about 120° F. in a 24-hour cycle to the black stage and finish in the sun. Coffee damaged by incorrect methods of drying develops a characteristic brown-yellow'color end a sour and unpleasant liquor results. Laboratory experiments have confinmed the field-scale findings and investigations aimed at determining the circumstances under 24 which losses of quality occur, have given the following tentative findings: 1. Fully wet coffee will be severely damaged by a single- stage drying at any temperature over 100° F. 2. The lower the initial moisture content at which mechanical drying is started, the less is the damage, at any temp- erature over 100° !. 3. Sunlight is probably not an essential factor. 4. Severe damage to quality caused by mechanical drying is probably associated with damage to viability. S. It is possible that a critical temperature below 1000 P. exists, below which fully wet coffee can be dried in one stage without damage. Ball (1957) presents fully the theory of drying and points out that there is a difference between canon drying and mechanical drying of farm products. He points out the effect of drying t-perature on viability and on the chemical struc- ture and composition. Results obtained by other researchers in a specific crop like coffee are actually confirming this 8 tatement . McCloy (1958) reported that the use of artificial radiation has about that color development during drying of coffee beans is photo-sensitive. To avoid loss of quality, machine drying at low temperatures, should be combined with sun-drying. ne reco-ends that coffee beansbe stored at less than 151 moisture content, w.b. , and points out that coffee deterioration 25 during bin storage may be reduced by the use of perforated floors and small cold air fans. Ulrich (1958) found that when plotted the water lost by a crop (transpiration) versus the time element gives a straight line. The linearity obtained is a function of the vapor pressure gradient difference and the slope of the curve is due to the nature of the cuticle or surface. Bguilibgim moisture content. Coleman and Fellows (1925) determined the moisture contents for cereal grains and flax seed exposed to 15, 30, 45, 60, 7s, 90 and 100 percent relative humidity and 25° c. (77° 3.) temperature . Burton (1941-42) found that equilibrium moisture in static chm-hers was attained in 29 days for onions, tomatoes, pine flax, lettuce and peanuts when exposed to atmospheres of 35, 55 and 76 percent relative huidity and 30° C. (86° 1'.). Fluctuations after that period of time were attributed to weighing errors. Variation in the absorption of water by seeds of the same variety under sane relative humidities, but at different temperatures, which were not expected were observed. The explanation of this phenomena must be sought not only on the physical conditions of the atmosphere sur- rounding the seed but in the physical condition of the seed itself. Similar variations were observed in the .parcl-ent coffee beans . 26 Johnston and Poote (1951) pointed out that the coffee curing process to produce good quality depends on the substitution of controlled pectic enzyme action for spontaneous fermentation and substitution of rapid drying for slow and inefficient drying. Barton and Goenga (1952) studied the reliability of a tester for measuring the moisture present in "coco" coffee. "Coco" coffee is defined as a heterogenous mixture of whole fruits, broken fruits, clean seed and fruit costs. They found that when the moisture content is in the range of 10 to 23 percent of the dry weight of the "coco" coffee the moisture tester can be used satisfactorily if a small correction factor of -l.75 percent was applied. There is no application for this data where clean, high quality coffee is produced. Lopez (1952) reported equilibriun moisture contents for parchent arabic coffee as determined from different storages. The objective was to find out how coffee fluctuates in its moisture contents with changing atmospheric conditions. Data obtained show that parchment coffee responds very slowly to relative humidity and temperature fluctuations as affecting its water contents. He points out that more detail and controlled research is needed. Goetz (1955) presents a technical discussion of living matter as affected by temperature an water contents. He classifies the state of living matter as active or inactive and applies the term biokinetic range for the first condition and biostatic 27 to the second. Ball (1956) determined the equilibrium moisture content for sugar beet seeds for 90, 75 and 53 percent relative humidity o and temperatures of 40°, 60°, 80 and 100° 1?. Hall (1957) discusses fully the equilibritml moisture contents of crops and explains its determination,.practical uses, representation and relations with vapor pressure, moisture content and temperature . Hall and Arias (1958) desorption isotherms covering a wide range of relative huidities and temperatures were worked out for corn. A cmaplete analysis was given of the drying theory and the discussion and adaptability of the existing formulae in the light of the information gathered. Electronic sorting. Curtis (1953) reported an installation of a battery of electronic sorting machines in California for the sorting of green coffee before being inspected by the 0.8. Customs. Curtis (1956) (1958) reported on the progress attained in green coffee commercial sorting and its effect on quality of the final product. 28 PROCEDURE Coefficient of friction and “iii of repose. The coefficient of friction for coffee fruit and coffee beans at different stages during the processing was determined for several of the most comonly used building materials. A conventional tilting table was used, as shown in Fig. 2. The fruits or beans were placed in bottomless, three inch diameter, one inch high galvanised iron containers. Due to the weight of the container it was impossible to raise it so that there will be no contact with the surface being tested. After several unsuccesful tests these were discarded and cardboard containers of the same shape and size were used. After placing the product in the container, and with the tilting table in a horizontal position, the container was raised until only the product one in contact with the surface. The table was slowly tilted until the seed slid on the surface. The angle was measured with a protractor. The tangent of the angle at which the product slid is the coefficient of friction. All tests where the product tilts or rolls were discarded. The data in Table 3 are the average of four successful tests where the product slid over the surface without rolling and the holding frame did not come in contact with the surface. The angle of repose of the product, or that is, when fruit or seed slides over itself was determined only for the ripe fruit, green fruits and parchment coffee. The limited anount of material available did not permit determinations during other stages in the 29 processing. To perform these determinations would have meant the simultaneous processing of all the product at once so the other tests could not have been performed. The angle of repose or the coefficient of friction of the fruit over itself was performed as follows: A box twelve inches wide, twelve inches long and six inches high was prepared with a round orifice two inches in diameter in the center of the bottom. A sliding gate on the underside of the bottom permits the opening to be closed or opened without moving or disturbing the box or the contents. The box was level on top of two blocks leaving the orifice free. The fruits were placed in the box and the gate opened. As the fruits flow out freely they come to their normal angle of repose. This angle was measured with a protractor, and also calculated by the function of the angle. Resiliency of green and ripe fruits. The rebomding characteristics of the fruit when dropped or projected against a surface were studied. The objective was to observe if the fruit, upon collision with another body, will respond as an inelastic, elastic or intermediate type collision. The information might be of interest for mechanical picking or sorting of the crop. A wooden frame four feet by four feet was built. A piece of co-ercial wrapping paper was fastened to the fr- ad a one inch hole cut in the center. This fine was placed level over the surface to be tested which was also level. An adjustablel’haight arm mo‘nlted on a £1:- base was prepared with a clip on the end to hold the fruit lightly. The clip could .. 30 Pig. 2. Tilting Table Used for Coefficient of lrictioa Determinations. Fig. 3. Iquipment Deed for keeiliency Studies. 31 be opened to drop the fruit when desired. In this way a uniform height of drop was assured with the least human intervention. The arm was adjusted for height, the clip centered on the hole in the paper and the fruits dropped one at a time against the surface being tested. Baby powder was spread over the paper so that the fruits left a clear spot in the place where they hit after rebounding from the surface, as illustrated in Pig. 3. The place where the fruit hit in the first bounce from the sur- face was marked. A mini-- of 500 fruits were projected in each test. The rebounding distances were measured from the center of the paper. Due to the lack of uniformity on the shape of the fruits a circular pattern resulted. For this sue reason pro- jecting against surfaces at an angle did not show any definite pattern and were discontinued. Spe_cific gravity and bulk density. The specific gravity of the green and ripe fruits was determined from a random sarmle. A Boerneregpur was used to assure the selection of a good representative set of one hundred green mid one hundred ripe fruits. Distilled water at known temperatures was used for the determinations by the conventional Archimides principle. Fresh coffee fruits do not absorb water readily due to their almost impervious covering and due to the fact that the intra-cellular space is saturated so there is no water vapor pressure gradient at a uniform teqerature and under saturation conditions. The average density for ripe and green fruits was calculated. The fruits that floated in the water were discarded for upon checking them they exhibited aborted embryos . 32 4. Specific grutty .1 W1 t at fruit in lit apparent loss of weight in water The bulk density for green and ripe fruits and the pulp were obtained by weighing a certain quantity of the product and then measuring the voll-e this s-e count occupies when in a normal state. Bulk density = '31 t volume Air flotation and air conveygg velocities. The air flotation velocities were determined for the green and ripe fruit, fresh pulp, and pulped washed wet coffee beans. A pitot tube installation in a 1 5/8 inch plastic tube was used. The pressure difference (Pg-P1) between the static pressure tap and the impact pressure tap was measured with an inclined tube type manometer (Type C Intro-nanometer) so as to expand the scale and be able to read more accurately low pressure differentials. A screen placed above the pitot tube installation and at 12' inches from the top of the tube was provided to hold the sample being tested. Air was supplied by a Type P, electrically powered, k h.p., 3400 rpm fan manufactured by the Electric Ventilating Conany. The volt-e of flow and the velocity of flow in the plastic tube were controlled by a sliding gate installed on the inlet opening of the fan. The air velocity for flotation was determined for fifty sqles in each case taking the average of five readings. Flotation velocities required, in fpm. were calculated using the pitot tube formulae adjusted to the room air conditions (Bckman,'1957). m conveying air velocity was figured by adding 30 fps or .1000 fp- to the flotation velocity. (The results obtained fit very closely 33 5. on the conveying velocities in fpm curve, developed by the Sturtevant division of the Westinghouse Electric Corporation in 1946 and reproduced in the 1958 Agricultural Engineering Handbook (page 86 Pig. 8). The equipment used is shown in Fig. 4, Air flow relationships . Information on the resistance of coffee fruits and coffee bear to air flow is essential for the storage of the fruit previous to processing, for drying the processed beans ad for keeping the dried beans in storage. To perform the determinations a centri- fugal, radial flow, electrically powered fan was used to supply the air. The outlet of the fan was connected to an air-tight plywood box with a three and one-half inch inside di-eter galvan- ised piping. A sliding gate was provided at the entrace to the box ad aother at the outlet side to obtain the desired flow. The inlet and outlet to the box were located at a 90° angle. This box served to eliminate the air turbulence and provided a uniform steady air flow. From this setting boo: the air passed through a three inch inside diaeter galvanised iron pipe into a smaller box that served as the base for the coffee beans holding tower. A three inch inside di-etar pipe, five feet long was prepared to hold the sale. A flags with four equally spaced holes was welded to the bottom of the pipe to mount it on top of the receiving box and directly on top of a three inch bore. A screen was soldered to . the lower end of the pipe to hold the ample. One quarter inch taps were soldered to the pipe at one foot intervals from zero, i-ediately over the screen, to four feet in height. 34 ”M ‘ -:.- 1 \ , WV . . l ‘5‘. ’L’K a l a“? . x . / t—v. .. l'ig. 4. Equipment Deed to Determine Air Flotation Velocities. fig. 5. Equipment Used for Air Flow kelationship Studies. 35 6. A vena contracts, orifice type, flow meter was built and installed on top of the tube containing the sample to measure the air flow. A slanting tube manometer as described under Procedure-Air flotation was used to measure the pressure differences. Pig. 5 shows the installation used. Air flow rates varying from 10 to 70 cfm per g square foot were used. The air flow rates were calculated from . air flow pressure drop curves, Fig. 8, ad also from data provided by ten Engineering Handbook, Pig. 9. Emsed dying of washed coffee beans. Exposed drying, also called thin layer drying, refers to the drying of a product in a thin layer of one unit thickness so that the whole unit is exposed to the air moving around it. The in- formation can be used to determine the effect of temperature and air flow on drying. The coffee beas used for these tests were hand peeled, fermented for 12 hours and then washed in distilled water. The fermentation period is needed to eliminate the mucilage covering the beas. Distilled water was used to wash the samples so as to avoid mineral deposits on the outside coating of the beans which might interfer with the drying process. To supply the heated air for drying, hair dryers which have a resistance coil which can be adjusted for different tenperatures, were used. To provide a place to expose the beans to the air flow, a three and one-quarter inch inside diaeter piece of pipe was connected to the hair dryer outlets. All junctions were sealed so no air leaked. out through the sides. A three inch inside diameter, tray with wire mesh (window screen) bottom was built for each one of the units to hold the smsples. Tape was wrapped around each tray so no air 36 7. escaped through the sides. A thermometer was inserted inediately below the trays to obtain the temperature of the incoming air. The desired temperature was regulated with a variable resistance. The air flow was measured with a one inch vena contracts type ' orifice in a three inch pipe. The pressure differential across the restriction was measured with a slant tubs Type c micro- manomster as described previously. The sales were weighed in an analytical balance at the beginning of the test and periodically afterwards as show: in Tables 13 to 18. The final drying was done in an air ova at 100° c (212° 1r) for 96 hours. m temperatures used were: 85° r. 100° a, 120° 2, 140° 3, 160° 1! and 180° 1r. The air flow was 92 fpm or 4.5 cfm per square foot. The average relative humidity of the incoming air was 351. Three indspadent determinations were averaged to get the results for each temperature used. The equipment used for the tests are shots: in rig. 6. Eggilibriu moisture content for pflbent coffee. The hygroscopic equilibrims of a product can be determined either by a static or dye-it method. In the first case the product comes to equilibrium with the surrounding atmosphere without . agitation of air or product. In the second case either the atmosphere surrolalding the product or the product itself are moved or agitated in relation to each other. The static method requires longer periods of exposure to reach equilibrilaa but is siqle to do. Care was taken so that the total surface area of the saple does not exceed the surface area of the liquid used to regulate the relative huidity. The individual beans were kept separated as there 37 r13. 6. leuipmsnt Used for Parchent coffee Drying. was no direct contact between them while exposed to the treatment. These precautions are not so critical in the dynuic chder deteruinations. In the equilibriu moisture content determinations for parcl-ent coffee, both the dyn-ic ad the static methods, were used independently. tor the higher teweratures, 100° r and 86° r. a dyn-ic oh-ber available in the Agricultural Engineering process- ing laboratory was used. Saturated aqueous solutions of chemically pure salts were used to maintain the desired relative htmidity in the thermostatic ch-bers. Above room teqeratures are ' easily naintained in the dyn-ic chders. For lower than room toner- atures, where the dye-1c ch-bers present a cooling problem, the static method was used. One gallon neson jars were prepared with a good sealing threaded lid and gasket. A wire hook was soldered in the center of each lid to hang a wire basket containing the e-ple. The wire mesh baskets were eade round, slightly smaller th- the mason jar opening and with a convex button. In this way the individual beans were scattered in the perifery and do not group up while screwing the lid. One thousm1d cubic centimeters of the saturated salt solution was placed in each jar. These were not opened except for the brief periods of weighing. To insure saturation of the salt solution for a particular taperature the solution was prepared at a higher teqerature thn required. Upon cooling to the desired temperature some salt crystalitation was observed in each case. The temperature was naintained within f_ 1° r. either by adjustments of the rehoetats in the dye-ic chnbers or by placing the lieson jars used in the static determinations in temperature controlled coolers. Ripe coffee fruits were pulpsd, fermented for 12 hours, washed in 39 distilled water, weighed and placed in the controlled chambers or jars. Periodical weighing in an analytical balance were taken until a uniform weight was obtained. This was considered the equilibrium moisture content for the conditions under consideration. The dynanic chader determinations were carried on for 624 hours and .the static ones for 2200 hours so as to be sure equilibriu had been reached. The final drying, to calculate the noisture contents of the coffee beans during different stages of the test, was done in an air oven at 100° c for 96 hours. The product was placed into the controlled conditions iamediately after washing off the nucilage at a moisture content which varies from 53 to 557., w.b. The curves obtained in this way are dnrefwe of the desorption type and being for a fixed temperature are called desorption isotherms. Sortiggfjreen and ripe coffee fruits. Ripe coffee fruits are picked by hand. No matter how careful the picker is, a variable number of green or partially ripe fruits are always present in the product. The percent of unripe fruits present varies considerably during the harvesting season. The last picking includes all the fruits left on the tree and the amount of green fruits present is considerable. If these are not sorted out before processing a dual problem results. First the quality of the whole batch will be ruined and second, there is considerable loss involved. Sorting, so far, is done by hand. A simple, efficient way of separation needs to be developed. Information on the physical properties of the fruit is very helpful for mechanical sorting. Separation by color using the principle of a photo-sensitive cell also offers posibilities. 40 Proper feeding, photometric principles and electronic controls are the three fundamentals to consider in this type of sorting. A mixed s-ple of green and ripe fruits were run several times through a Gunson's Electronic Separator installed by the Sorter Company of North.America at Lowell,‘xichigan. The general principle on which this machine works are as follows: The commodity is fed fromvthe hopper by means of a vibrating chute so as to align on a grooved belt. As the belt moves forward the product is projected in a single stream to a point in the optical unit where each component is evenly illminated and viewed fro. two nearly opposite sides against a background. Any variation from the bulk color will produce a variation of light received as compared with the steady reflection given.by the background. The point of observation is focussed onto a scanning slot behind which is situated a light sensitive device (photo-cell). Any variation of color will cause a pulse to be given by this photo-cell which, after amplification according to control setting, raise the voltage in a pair of needle tehminals to about 20,000 volts. The passing particles are electrically charged by these needles as they fall through. The product being sorted continue to fall in their natural trajectory into an electric field created by deflectors which only act upon the charged particles. The deflection caused is enough to change the trajectory and the charged particle falls to one side of a dividing edge. The non-charged particles follow a normal trajectory and fall to the other side of the divider. One streau.consists of uncharged particles falling naturally and the other of the charged and deflected ones, of different color. 41 RESULTS AND DISCUSSION Coffee is a crop which requires considerable handling and processing in the farm before it is ready for the market. During this processing period, which includes numerous steps, the product is moved several times. In the design of the structures and equipment the main problem encountered is the lack of basic information about the crop itself ad how it behaves in relation with construction materials. Host coffee in Puerto Rico is grown on hilly land where the slope of the terrain could be very well used to advantage for a gravity flow system. Fig. 1 shows a proposed plan for a simplified processing system in which the product is moved through the plant mainly by gravity, saving consid- ‘ erable labor and power. To construct the necessary facilities for such an installation the angle of repose and the coefficients of friction between the product, at different stages of processing, and the construction materials must be known. Table 3 gives the results obtained for the angle of repose and coefficient of friction as determined by the tilting table method for the main construction materials used in coffee processing. Values for materials that are not adaptable to be used at certain stages of processing are-not included. Higher values obtained for wet surface product on wood are expected since the grain of the wood upon soaking water becomes rougher. The removal of the excess free water i-ediately after washing ad before drying, in a simple continuous process, is a challenging problem. Coefficients of friction for perforated steel and wire mesh were determined only for washed wet coffee beans where the 42 excess water could probably be sieved out while the beans slide over a surface. Research work similar to that conducted in Hawaii for the passion fruit juice extraction night be the solution (Kinch, 1958). 43 Table 3 Coefficient of Friction of Coffee Fruit and Coffee Beans Ripe Green Pulped Pulp Washed Dry Fruits Fruits Unwashed Wet Deas Treatment gains Degas DsSs “.8. DsSs ".3. a b _ a b c c d e Concrete (Wood Bloated) 0.64 0.59 0.64 0.62 0.94 0.70 1.03 0.55 Concrete (As taken from forms) 0.68 0.55 0.59 0.59 0.93 0.62 0.98 0.51 Rough Hood (with Grain) 0.61 0.75 0.77 0.85 Rough Hood (Across Grain) 0.68 0.74 0.59 0.66 Planed flood (With Grain) 0.61 0.70 0.510.67 0.90 0.75 1.07 0.42 Planed Wood (Across Grain) 0.61 0.66 0.59 0.67 0.93 0.81 1.15 0.49 Plywood (With Grain) 0.59 0.69 0.50 0.60 0.47 Plywood (Across Grain) 0.71 0.55 0.62 Galvaiaed Iron 0.47 0.50 0.47 0.54 0.60 0.87 0 64 0 57 Alain:- 0.58 0.52 0.54 0.47 0.49 0.58 0.78 0 64 0. 8i: 13 Stainless Steel 0.55 0.49 0.45 0.65 °999° 8 Steel 59 0.49 0.59 0.58 0.65 0.73 0.90 .53 Steel ~Perforated lll6 Dime. 8/sq. in. 0.90 Steel -Perforated 1/8 Dia. l6/sq. in. 0.90 Steel-Perforated 5/32 Diau.16/sq. tn. . 0.90 Steel-Perforated 3/16 Dia. 13/sq. in. 0.75 Window Screen 14:18 Mesh 0.78 0.79 0.65 0.65 1.11 Green Pruit 1 . 33 Ripe Fruit 1 . 15 a Dry surface d I-sdiately after washing b Wet surface e 12% moisture d.b. c Iaediately after pulping 44 The results of the preliminary rebounding test for ripe and green coffee fruit show some possibilities of obtaining a definite pattern. The ripe fruits, being covered by a mucilagenous substace which makes them softer, rebound, in general, a shorter distance than the green, harder fruits. The results of a single series of tests with limited aount of material should not be considered conclusive. This phase of the test is postponed to be continued at a latter date during the following coffee crop season. Projecting the fruits against surfaces at an agle to the path was not satisfactory. The great variation in shape of the fruit ad the form in which these hit the surface resulted in a very scattered pattern. Best results were obtained when the fruit ad the surface being tested meet each other at a 90° agle. Steel, concrete ad wooden surfaces were tried at different dropping heights. Results will not be published until enough replications are performed to insure a dependable statistical analysis. Fig. 3 shows the equipment used for these preliminary tests. In the saples studied very little difference was found in the average specific gravity and density of green and ripe fruits. The specific gravity for the green fruits varied from. 1.0063 to 1.1163 ad for the ripe fruit from 1.0072 to 1.0884. Contrary to expectations the green fruits showed a higher average specific gravity than the ripe fruits. The higher average value in specific gravity and density of the green fruit seems to be due to some physio- chemical changes that occurs on ripening. The result of one hundred individual determinations of green ad ripe fruits fluctuate so mach that there is no way of expressing my significant difference for green and ripe’fruits. The values obtained for specific gravity, bulk density 45 and void space for coffee compares with the values obtained for wheat, oats, corn, buckwheat ad millet by link (1935) and by the 0.S.D.A. (n.d.) Table 4 ad 5 show the results of these tests. 46 Table 4. Specific Gravity and Density of Green ad Ripe Coffee Fruits Fruits Specific Temp. of Water Mt Density a Gravity ° F. ‘ ‘ Grams/cu. cm. Pounds/cu. ft. Green 1.0722 * 79° 3. 1.0687 66.76 Ripe 1.0454 ** 80° 3. 1.0415 65.07 Table 5. Bulk Density of 'Coffee Fruits and Coffee Pulp Fruits or Number of Fruits Weight Density Void Space Pulp b b Percent Per cu. cm. Per cu. ft. Grams/cu. cm. Lbs/cu. ft. b Green 0.546 15,460 0.601 37.54 44 Ripe 0 . 361 10 .222 ' 0 . 596 37. 24 43 Pulp c 0.248 15.48 a Average of 100 determinations b Average of 20 determinations c Freshly removed pulp * Ranges from 1.0063 to 1.1163 ** Ranges from 1.0072 to 1.0884 47 The preliminary work by other researchers on pneumatic conveyance of material was done on ensilage cutters ad blowers. In 1946 the Sturtevat Division of the Westinghouse Corporation developed a general curve for conveying velocities based on the bulk weight of the material being conveyed. The basic equation for a pitot tube fluid velocity measure- ment is as follows: V 8 Opt V(d. - df) v V Zgh (Eckman, 1957) where V " Velocity of flowing fluid, feet per second cpt Velocity coefficient, a constat, approx. 1 dm Density of manometer fluid, pounds per cubic foot df Density of fluid over the manometer fluid, pounds per cubic foot v 3 Specific volume of the flowing gas, cubic feet per pound Acceleration due to gravity, feet per second per second h = Macmeter differential, feet Since df 0 s 32.2 Then \fl62.4) (64.4) V]: As h is measured in inches of water let h = 4:2: V And V -'- V 62.4 64.4 Vh' 12 V 3 $34.2 vh' Using 5 v 3 14.5 v = K3341) (14.5) h' V = 69 V h' in feet per second v. = 4140 h' in feet per minute 48 The generally accepted pneuatic conveying velocity is the flotation air velocity plus frm 30 to 50 feet per second. The values obtained for coffee fruit, pulp ad boas are presented in Table 6. When these values are calculated with the above for-alas they come very close to the values for conveying velocities obtained by using the Sturtevat air conveying curve as shown in Table 6 and Fig. 7. The Buffalo Forge Co. (1949) mblished some generally used conveying air velocities based on the following formla: 1030\77' VT 7 582.5 VT:- v : V = Air velocity, feet per minute w 3 Bulk weight of material, pounds per cubic foot. d = Diaeter of equivalent cross-section of particle, inches. Using the sac bulk densities obtained .ad the average diaeter of the coffee fruit, which is about one-half inch, the results are also very close to the ones obtained by the previously discussed methods. 49 Table 6 Average Air Velocities for Conveying Coffee Fruits, Pulp and Beans ft/min. Material Pressure 'Flotation Conveying Bulk Sturtevat Inches Velocity Velocity Density Conveying Of Water a b c Velocities d Green Fruits 0.881 3,883 5,683 37.54 5,600 Ripe - Fruits 0.910 3, 950 5, 750 37.24 5,550 Fresh Pulp 0.572 3,125 4,925 15.48 4,100 Pulped Washed Beans 0.786 3,655 5,455 m 6500 1001 .— :5 E z 6000 90' a: w . ° 5500 o 804 r- 2 Lu 3 m 0 ‘k 5000 “- 70. " n: E e ‘ 8 4500 m 60d 4 2 U u. >4000 ° 50. L9 1- .2. S g 3500 “'40 > 2 z 8 5 10 1'5 2'0 2'5 3'0 3'5 30 4'5 50 BULK WEIGHT OF MATERIAL, POUNDS PER CU. FT. Fig. 7. Average velocities and air voltaes for conveying material. Reproduced by permission of the Sturtevat Division, Westinghouse Corp. a Calculated by 56mm 4140 h' b Flotation velocity I 1800 fpm c From specific gravity determinations d From Sturtevat conveying curve 50 The data obtained for the resistance of air flow per each foot depth of coffee fruits ad coffee beas during different stages of processing are presented in Tables 7 to 12 ad Fig. 10 to 13. Hall (1957a) points out that the static pressure varies directly as the depth of the product, with a linear relationship between the static pressure ad depth. When the static pressure versus air flow data are plotted on logarithmic paper a nearly straight line results which ca be expressed by the following foremla: Q‘ = a. P'b. Q. 3 Air flow, cubic feet per minute per square foot a. 3 Constat P' = Static pressure drop, inches of water b. 1’ Exponential value which represent static pressure relationships in crop drying. Shedd (1953) states that the resistace to air flow is increased if foreign material finer tha the product is present ad reduced if the foreign material is coarser. The tests were performed with coffee fruits or coffee beas capletely free from foreign material. Air flow versus pressure drop relationships in coarser material gives a straighter line, when plotted logarithmically, than finer material for coffee fruits or beas. The voline of air flowing through the product was converted from inches of water to cubic feet per minute ad then to cubic feet per minute per square foot of area for a 3 inch inside diaeter pipe used for the determinations. Calculations following the Fa Engineering Handbook data ad formula, as presented in Fig. 9 j and following the air flow pressure drop curves shown in Fig. 8, come Very close, Anyone of these could be used to calculate the air flow 51 if the pipe diameter ad pressure drops are known. Ripe coffee fruits offer a higher resistace to air flow tha the green fruits. In ventilating or cooling a batch of mixed or partially ripe fruits this must be taken into consideration. In the washed parchment beas the higher the moisture content the higher the resistace to air flow in general. Dryers not be designed on the maxi-am resistace to take care of the initial drying period. Table 7 Resistace of Green Coffee Fruits to Air Flow Pressure Drop - Inches of Water cfm/sq. ft. 1' 2‘ 3' 4' 46 0.102 0.204 0.306 0.418 62 0.170 . 0.332 0.497 0.680 84 0.276 0.536 0.804 1.104 103 0.382 0.746 0.940 1.530 118 0.495' 0.962 1.442 1.980 133 0.601 1.168 1.752 2.405 52 1.2" '41 29 L7 l.5 L3 I24 Ll" l0+ 10" 8+ 0.9“ 66‘ 0.8" '23 3. O .1 u. 4. a: 2 .6" ' /0.5' 21 _. 1:" 3" inside diameter Di” (0) 0 . p. i'op I L I .l .2 .3 -4 '5 FIG.8 PRESSURE DROP THROUGH ORIFICE, INCHES OF WATER 2 L8 0.900 [i'('%) J 0= 40050AVp 53 0.901 0.86- 0.847 0.80% m In 30.76 <1 > 'o 0.72J On 4005 CA VII/2 Oscfm C I cost. of discharge 0.68‘ Az/A a ratio of orifice ' to pipe diameter h :- inches oi woier' o 64" A" ("00 Of pipe, 0' A2: area of orifice,c1‘ v” 0 0.'l 0.2 0'4 0.6 0.0 A / ZAI .. .. FIG.9 COEFFICIENT OF DISCHARGE C FOR A In" VENA-CONTRACTA ORIFICE IN A 3" PIPE (FROM FAN ENCR. HANDBOOK) 54 AIR FLOW, cfm pern’ a 9.... 1 I I A A '8’ as 9 OI 9 20 N-I uJ INCHES OF WATER FIG. I0 RESISTANCE 0F GREEN COFFEE FRUIT TO AIR FLOW PRESSURE DROR Table 8 Resistance of Ripe Coffee Fruits to Air Flow Pressure Drop ~ Inches of iiater cfm/sq. ft. 1' 2' 30 4. 46 0.170 0.354 0.530 0.680 58 0.264 0.562 0.842 1.075 84 0.496 0.970 1.250 1.850 103 0. 657 1 . 378 2 .067 2 . 630 112 0.761 1.590 2.385 3.043 Table 9 Resistace of Washed Wet Parchnent Coffee Beas to Air Flow Pressure Drop - Inches of Water cfm/sq. ft. 1' 2' 3' 4' 11.0 0.067 0.136 0.204 0.268 14.0 0.105 0.208 0.312 0.418 20.0 0.188 0.378 0.567 0.754 30.0 0.335 0.677 1.015 1.340 45.0 0.508 1.014 1.521 2.032 60.0 0.760 1.607 2.411 3.240 a I-ediately after washing Percent Moisture, w.b. At Beginning of Test 55.6 At End of Test 53.5 56 o 9 cfm perch, 6 0 AIR FLOW, 0 O 9 . 9 . . 4 N-I 2°. 3 3 .7. r .6 'F‘Ifo PRESSURE DROP, INCHES OF WATER FIG.” RESISTANCE 0F RIPE COFFEE FRUIT TO AIR FLOW 57 Table 10 Resistace of Washed Parchment Coffee Beas to Air Flow . PJrEessure Drgp 43b» of Raga cfm/sq. ft. 1' 2' 3‘ 4' 11.0 0.058 0.107 0.175 0.220 21.7 0.146 0.293 0.440 0.585 31.3 0.259 0.532 0.796 1.025 40.7 0.386 0.765 1.147 1.535 48.0 0.467 0.943 1.415 1.870 67.5 0.683 1.354 2.031 2.733 72.0 0.770 1.537 2.305 3.080 a Air dried for 6 hours Percent Moisture, w.b. At Beginning of Test 52.0 At End of Test 49.1 Table 11 Resistace of Washed Parchment Coffee Beas to Air Flow . Pressure Drop - Inches of Water cfm/sq. ft. 1' 2' 3' 4' 11.0 0.086 0.165 0.250 0.335 21.7 0.196 0.393 0.590 0.785 31.3 0.326 0.643 0.965 1.305 40.7 0.456 0.910 1.435 1.825 48.8 0.556 1.102 1.653 2.225 60.6 0.782 1.560 2.340 3.130 a Air Dried for 24 hours Percent Moisture, w.b. At Beginning of Test At End of Test 58 cfm pero’ AIR FLOW, washed wet coffee beans percent moisture, W.b. beginning of test- 55.6 end of test - -- - -53.5 m _. l on o 20‘ 4' bath washed coffee beans percent moisture, W. b. ‘ beginning of test-52.0 end of test - ---49.I A I0 .2 .3 .4 .6 ' .8 ' I'o PRESSURE DROE INCHES OF WATER FIG. l2 RESISTANCE‘OF PARCHMENT COFFEE TO AIR FLOW 59 Table 12 Resistace of Dried Parchment Coffee Beas to Air Flow Pressure Drgp - Inches of Water cfm/sq. ft. - 1' 2' 3' 4' 15 0.111 0.220 0.330 0.443 21.7 0.180 0.363 0.534 0.730 31.3 0.305 0.607 0.910 1.220 40.7 0.420 0.837 1.255 1.680 48.8 0.536 1.082 1.622 2.145 60.6 0.741 1.476 2.214 2.965 a Air Dried for 10 Days . Percent Moisture, w.b. At Beginning of Test 13.3 At End of Test 11.7 80‘ 4e Washed coffee beans percent moisture, W.b. beginning of test--45.4 end Of test-------45.0 , cfm per :1’ m .— 1 9 I o m 9 J AIR FLOW n 9 3 dried coffee beans 20- percent moisture, W. b. beginning of test-43.3 end of test-------II.7 I0 . . e 4 T . - . . . e .l 2 3 4 .6 .8 IO 2 3 PRESSURE OROR INCHES OF WATER FIG. I3 RESISTANCE OF PARCHMENT COFFEE TO AIR FLOW 61 Drying is the bottleneck in the processing of the coffee for the market today. The fermentation period required for the removal of the acilage used to be the main problem in a continous operation. With the development of the caustic soda or chemical method by Carbouell, ad Vilanoua, (1951-52) at El Salvador ad with the recent development of ‘mechanical scrubers and washers this problem.was solved. The drying problem.is, however, still present and when the harvest season is in its peak the farmer must find a way to dry the coffee to a safe storage moisture content as rapidly as possible without damaging quality. Coffee Inst be dried immediately after washing or store for very short periods of time under running water. Sun drying was the common practice some years ago. This requires considerable space, facilities and labor. Heated air drying is becoming the common practice today on all farms. Basic drying data for coffee is lagging behind instead of being ahead of the dryer's design. Dryers specifically built for other crops have been and are utilised for coffee drying with considerable disadvantages. The only organised research in coffee drying of which there is ay available information was conducted in Peru by Ives (1955) the results of which has been fully discussed. The coffee bean, after washing, is surrounded by two layers of tissues ad an air space between them. This condition greatly hinders the move- ment of water from the inside towards the surface unless a great vapor pressure gradient is created or long periods of drying are considered. . Another important point to consider in drying coffee is the quality of the final product. Temperatures above 120° F . has repeatedly proven detrimental to the coffee quality as discussed previously. The effects 62 of temperature on the color of the outside coating of coffee beas ca be observed on color pictures, Fig. 17. The exposed drying curves for the rage of temperatures from 85° to 180° F. shows the required drying time for fixed air flow rate ad relative humidity. The rate of drying presented in Fig. 15 ad 16 also gave a indication which ca be used as basis for better drying methods. ' Vacuum drying will probably be the aswer to rapid, efficient, quality conserving drying of coffee. 63 Table 13 Exposed Drying Rate for Coffee Beans a reap. 'l‘ine Percent - dis ’Ilh ° F. Minutes Moisture, d.b. d-o " 0 120.6 2 115.9 141.0 4 113.0 114.0 6 110.7 99.0 8 108.7 89.2 10 107.2 80.4 12 106.0 73.0 14 105.0 67.0 16 164.2 62.3 18 103.5 56.4 85 20 102.8 53.4 25 101.7 45.4 30 100.9 39.4 40 99.6 31.5 60 98.0 7 22.6 90 95.9 16.5 120 93.9 13.3 240 86.8 8.4 360 78.8 7.0 540 67.1’ 6.0 720 50.5 5.8 1440 27.0 3.9 2160 11.9 3.0 3000 8.8 2.2 a Air Flow 92 fpn, 4.5 cfn per sq. ft. Average Relative fluidity 351 Average ‘l‘hres Deterninstions 64 Table 14 Exposed Drying Rate for Coffee Beans ‘ Tine Percent 13.5: Minutes Hois ture , d.b . *3? Zlhr. 0 120.5 2 115.2 159.0 4 111.8 130.5 6 109.1 114.0 8 106.9 102.0 10 105.2 91.8 12 103.9 83.0 14 102.7 76.5 16 101.7 71.4 18 100.9 64.7 20 100.2 60.9 25 98.7 52.3 10° 30 97.7 45.6 40 96.1 36.6 60 93.2 27.3 90 89.5 20.6 120 86.8 16.8 240 71.5' 12.2 360 59.4 10.2 540 41.8 8.8 720 29.1 7.6 1440 9.7 4.6 2160 7.4 3.2 3000 6.4 2.3 a Air Flow 92 fpm, 4.5 cfn per sq. ft. Average Relative fluidity 352 Average of Three Deterninations 65 Table 15 Exposed Drying Rate for Coffee Beans Temp. Tine Percent L, Ilhr. ° F. Minutes Mois tureL d.b. d 0- 0 120.7 2 113.8 207.0 4 109.5 168.0 6 106.5 142.0 8 104.4 122.3 10 102.4 109.8 12 100.3 102.0 14 98.3 96.3 16‘ 97.1 89.7 18' 95.7 82.5 20 95.4 75.9 25 93.2 66.0 30 91.7 58.0 12° 40 88.7 48.0 60 80.7 40.0 90 68.2 35.0 120 64.7 28.0 240 32.7 22.0 360 24.7 16.0 540 23.5 10.8 720 22.3 8.2 1440 5.5 4.8 2160 5.2 3.2 3000 5.0 2.3 66 a Air Flow 92 fpll, 4.5 of. per sq. ft. Average Relative fluidity 351 Average Three Deter-inst ions Table 16 Exposed Drying Rate for Coffee Beans Tgnp. Tine Percent __d_n__’ Ilhr. P. Hinutes Moisture, d.b. d-O- V— 0 119.6 2 111.7 237.0 4 107.0 189.0 6 103.0 166.0 -8 100.0 147.0 10 97.5 132.6 12 95.2 122.0 14 93.6 111.8 16 92.2 104.1 18 90.9 94.7 20 89.8 89.4 25 87.3 77.5 30 85.3 68.6 40 80.9 58.0 1‘0 60 72.7 46.9 90 59.6 40.0 120 50.2 34.7 240 19.9 24.9 360 10.5 . 18.2 540 7.1 12.5 720 6.0 9.5 1440 4.4 4.8 2160 3.9 3.2 3000 3.3 2.3 67 a Air Flow 92 fpl. 4.5 cfn per sq. ft. Average Relative fluidity 351 Average of Three Deterninat ions Table 17 Exposed Drying Rate for Coffee Beans Ten. Tine Percent L ° 1. flinutes Moisture, d.b. d-O- 0 116.1 2 107.2 267.0 4 102.0 211.5 _6 98.7 174.0 8 96.0 150.7 10 93.6 135.0 12 91.7 122.0 14 89.9 112.6 16 68.0 106.8 18 86.3 98.3 20 84.7 94.2 25 80.5 85.4 30 76.0 32,7 16° 40 69.2 70.4 60 56.6 59.5 90 40.6 50.4 120 28.7 43.7 240 10.7 26.3 360 7.6 18.1 540 ' 5.7 12.3 720 4.8 9.3 1440 ‘ 3.5 ' 4.7 2160 2.7 3.2 3000 . 2.3 2.3 a Air Plow 92 fps, 4.5 cfn per sq. ft. Average Relative fluidity 351 Average of Three Deterninatioas 68 Table 18 Exposed Drying Rate for Coffee Beans A— 131: 81:11:36 3613:3221. '72,"; “h" 0 125.7 2 115.8 297.0 4 109.0 250.5 6 104.2 215.0 8 100.2 191.3 10 96.0- 178.2 12 92.4 166.5 14 89.0 157.8 16 85.6 152.4 18 82.6 142.2 20 79.5 138.6 25 70.8 131.8 180 30 64.0 123.4 40 53.4 108.5 60 34.5 91.2 90 19.9 70.5 120 12.4 56.6 240 6.6 29.8 360 5.0 20.1 540 4.2 13.5 720 3.5 10.2 1440 2.3 5.1 2160 1.9 3.4 3000 1.5 2.5 69 a Air Plow 92 fpn, 4.5 cfn per sq. ft. Average Relative fluidity 351 Average of Three Deter-inations PERCENT MOISTURE, d.b. 04 9 N C? ...,....——- — (9‘ 60‘ . 15' 1:5 “540‘ a: :3 i— 4 Q 0 5 20+ ,- 2 Lu 0 '4 c: 11.1 0. \“~\ 0 r 1"‘ T Y I r I 1"“ 1 fl \ 6O lZO 180 240 300 360 \\\\\\\ MINUTES X \ air velocity, 92' per minute \ 4.5 cfm per 6' x \\ average relative humidity 35% 0\ each point: 3 determinations x— 85°F AMA- I40°F IOO°F -+--—+- |60°F 3 l20°F --—-—-—-—- |80°F Jt++ij> 158 :L HOURS FIG.I4 EXPOSED DRYING OF PARCHMENT COFFEE 7O I8 q T TEMP. EXPOSED DRYING EXPOSED DRYING RATE I °F HOURS °/. MOISTURE PER HOUR E 85 9 60 I I2 58 I60 I, 24 3.9 ' 36 3.0 50 2.2 I I00 9 88 I2 7.6 1 , 24 4.6 I40 }? 36 3.2 $ ~\ 50 25 E \. cnrnow 92fpn1 I20 9 I08 ‘- \5 4.5 cfm per a’ '2 8’2 I204 " \ . . . 24 4.8 ', \ average relative humIdIty 35% 36 3.2 9' \ \\ each point: 3 determinations 50 2'3 u‘ " I40 9 I25 . I2 9.5 a: 24 4.8 gIOO 36 3.2 I 50 2.3 tr I60 9 l2.3 3 I2 95 .. 62 5; I 0580‘ 50 2.5 E 0, I80 9 I35 5 I2 I02 2 323 5.1 3.4 |-—6C)'1 50 205 2 LL] U (I LLI Q. —G———G— |40° F 'A—A‘ I60° F - ‘ \. ‘\‘\x\\\\ F’\\\. ‘2‘ \\\\\\\\%x\\\\\ -9-9w80°F ‘ \\ '1' \ .\.\\ \‘ b 9 //// // // r5 I// '1 // / 20* 40 8'0 I 20 I60 200 240 280 520 ?60 MINUTES FIG.I5 EXPOSED DRYING RATES OF PARCHMENT COFFEE 71 FIG. I? COFFEE FRUITS AND BEANS AT DIFFERENT STAGES OF PROCESSING 73 The equilibriu moisture content for a product, as the nae implies, is the state of balace in noisture content to which the product arrives under certain at-ospheric conditions. Equilibriu is obtained «an the rate of noisture loss fro. the product to the surrounding air is equal to the rate of noisture absorbed (flall, 1957a). It is, therefore, also known as hygroscopic equilibriu. It is a well knoa fact that water is a najor constituent of all plat tissue. It serves as a vehicle for the trasportation of orgaic ad nineral letters, as a concentration regulator ad as a shock absorber for sudden chages in atnospheric conditions. The hygroscopic equilibriu is very useful to predict whether a product will gain or lose noisture under certain conditions of tsaerature ad relative htaidity. 11118 is very siaificat Uh“ 66.1163 with a product that requires drying and storing for considerable tins as coffee. Once the equilibriu noisture content is keen the drying process is sonswhat sialified ad loss caused by over-drying avoided. As pointed out on the discussion of exposed drying, the coffee ‘bea (adospern) after processing, drying ad storage is still covered by a thin layer of cells co-only boa es silver skin, a air space ad ' aother thicker layer of cells known as the endocarp as shown in Pig. 18. The presence of these, practically iaerneable layers, with a air space between then lakes drying are difficult ad response to varying atmospheric conditions very slow. Desorption isotherms for perch-at coffee for teaeratures of 40°, 68°, 86° ad 100° P. are presented in Pig. 19 as obtained for three detenin- ations for the 86° ad 100° P. ad two deteninations for the 40° ad 68° F. 74 te-peratures . During the tests it was observed that the scales reached half-way to equilibriu noisture contents fast. To reach equilibriu, however, they took a mach longer tine. In the higher teaeratures, when the product was near equilibriu noisture content, considerable fluctuations started to occur. This is probably due to the severe cracking observed in the endocarp of the beas. The tests conducted with the Gunson's Electronic sorting nachine at Lowell, Michiga shows the following results: 1. The feeding nechaisl is not appropriate to hadle coffee fruits. The vibration is too violent ad the fruits jiaped out of the vibrating hopper. The ripe coffee fruit, no latter how gently it is hadled, always suffer sons bruises or scratches through which the ancilage oozes ad the fruits being sorted stick to the feeding belt. This results in a erratic projection which in turn affects the efficiency of the optical unit in scanning the fruit. A Inchine that sorts truly by color and not by shades and one that scas the fruit nore conpletely ‘is needed. There are instaces when a fruit which is ripe enough for processing still have sons areas of green tissue on the outside. In order to be able to continue the electric sorting studies, negotiations between the Sortex Conpay of North Anerica ad the Puerto Rico Agricultural Experinat Station have been arranged. One unit, under a loan agree-eat, is to be- installed in Puerto Rico for further studies on color sorting of coffee fruits previous to processing. 75 ' Fig. H—Meture fruit cross section- showing the pericsr (pol greatly reduced in thick- ness (32 Xl’. er.=exocorp ' cot.-_. otyledor m=mesocerp sn.:end0coro s.sl.:silver slIir Fig. IS—Meture iruit cross section. illustra- ting the pericerp and seed histological constitution. (IOO X). s.t.:‘am-rO"" ts...e pe.:pericoro en.;:ecd‘ .e'o p.t.‘:p8'.'sode Mane end.'-end.szomm sclxrsciereids el.—e- carp s.sl. :5 var aim in me -orD st.“~“'ra Pig. 18. Cross Section of a nature Coffee Pruit. Reproduced by pernission of Coffee ad Tea industry Basins. 76 2. mmuuoo #29210de no mPZMPZOU mmahmas. EDEmZSOw 9.0.“. €5.23: “.2532. ezmomma 00. cm om 3 om cm 06 P P F LI » “.600. mowm lillrlirl “.er I¢I®l¢| On I a O N 9 9'6 ‘81N31N00 aanlsiow 1N30838 0 t0 0 Q 0 In SW The coefficients of friction between coffee fruit, coffee beas ad different construction naterials were deteuined by the tilting table nethod. Deterninations were perforad for dry surface ad wet surface fruits, pulp, pulped unwashed, pulped washed wet ad pulped washed dry beas. When the coefficients of friction obtained for wet or dry surface fruits are conpared, they show a consistently lower value for wet surface fruits on all natal surfaces ad a higher value on all wooden surfaces. The pulped washed, wet beans show the highest coefficient of friction when conpared with fruits, pulp, pulped unwashed or pulped washed dry beas for all naterials of construction. Values rage fron 0.65 for stain- less steel to 1.15 for plaed wood. The washed dry beas (12 percent noisture content, d.b.) showed the lowest coefficient of friction when coaared with fruits, pulp, pulped unwashed or pulped washed wet beans. The values obtained vary fron 0.34 for stainless steel to 0.55 for concrete ad are sinilar to the values obtained by Kraer (1944) for rough rice on the sac naterials. The results of the prelininary rebounding tests for ripe ad green coffee fruits show possibilities of obtaining a definite pattern for separation. When projected perpendicularly against a rebounding surface the ripe fruits show a forn of inelastic collision response while the green ones rebound in what ca be classified as an elastic forn. Projecting the fruits against a surface at a agle does not show ay regular pattern due to the fruits' surface irregularities. 78 The specific gravity for green fruit varied fron 1.0063 to. 1.1163 ad for the ripe fruits fron 1.0072 to 1.0884. No consistent difference was found between green ad ripe fruits which could be used to edvatage in sorting. The values obtained for specific gravity, bulk density and void space for coffee are sinilar to the values obtained by 21111: (1935) ad by the 0.8,D.A. (n.d.) for wheat, oats, buckwheat and nillet. The air velocities required for flotation were deternined with a pitot tube installation. The convational pitot tube for-11a (Echa, 1957) was used to calculate these values. Generally fron 30 to 50 feet per second are added to the flotation velocity to obtain the conveying velocity. The conveying velocities obtained by calculation can very close to the required conveying velocities as deternined by the Sturtevat air conveying curve developed by Westinghouse in 1946. Exposed or layer drying of coffee frcn approninately 542, w.b. to below storage noisture contents (121 w.b.) showed that the coffee bea follows the general drying rate pattern as found for other grains. Teqeratures of 85°, 100°, 120°, 140° 160°, ad 180° 11. were used with a air flow of 92 fpn in a 3 inch tray which gave a flow rate of 4.5 cfn per square foot. Drying at high teaeratures (over 160° P.) caused a undesirable coloring of the bea ad tenperatures over 120° P. cause endocarp cracking. So far no practical way of quality naintaace with nechaical drying has been worked out. Desorption isotherne for parcbsnt coffee beas exposed to teaeratures of 40°, 68°, 86° ad 100° P. were deterninsd. Due to the nature of the outer layers, parchnsnt coffee is very slow on its reaction to varying atnosphsric conditions . 79 Electronic sorting of the fruits before processing offers good possibil- ities. Tests perforned, using a Gunson's Electronic Separator, shows that the nechaical feeding, ad the scanning systen need to be nodified for successful separation. CONCLUS IGS Coefficient of friction. During the different stages of coffee processing, the highest coefficient of friction of the product on all naterials of construction corresponds to the pulped washed wet beas. Values obtained rage frcn 0.65 for stainless steel to 1.15 for plaed wood. This is considerably higher tha the values deternined for other crops on the sac naterials. The washed dry beas showed the lowest values. These varied fron 0.34 for stainless steel to 0.55 for concrete which conpsre with results obtained for rough rice on the sac naterials. Resiliency. Ripe ad green fruits rebound differently when dropped perpendicular to a surface. A definite pattern ca be obtained. Green fruits rebound farther in general tha the softer ripe ones. Specific gravity ad bulk densig. No significat, consistat difference was found in the specific gravity of ripe ad green fruits. Values obtained for green fruits varied fron 1.0063 to 1.1163 ad for ripe fruits fron 1.0072 to 1.0084. Air flotation ad convezi_ng velocities. Air flotation ad conveying velocities for coffee fruit, pulp ad beas deternined ad calculated using the conventional pitot tube installation ad fornula, with nor-a1 air conditions, coaare favorably with work done for other crops. Air velocities of 5,447, 81 5,567, 4,168 feet per ninute were obtained for green fruit, ripe fruit ad pulp respectively when deternined ad calculated with a pitot tube installation and fornula as coasted with 5,600, 5,550 ad 4,100 feet per ninute when taken fron the Sturtevat conveying curve. Resistance to air flow. Ripe coffee fruits offer a higher resistace to air flow than the green ones. In pertinent coffee, the higher the noisture content the higher the resistace to air flow. A linear relationship resulted when the static pressure in inches of water as plotted logaritl-ically versus the air flow for coffee fruits and beas. 05133 rates. Past drying at high taperetures (180° P.) affects the color of the coffee bea. Exposed drying of coffee beans follows the sac general drying rate pattern as for other grains. Severe cracking of the endocarp was observed when beas were. dried at taeratures above 120° P. The teaeratures being used for coffee drying are too high for quality naintaace. Eguilibriu noisture contents. Parclaent coffee responds very slowly to chages in atnospheric conditions requiring long periods of exposure to reach equilibriu: During the tests, nold growth was not present even when the product was exposed to seaningly favorable conditions. At high tenperature ad relative huidity considerable fluctuations in noisture content were observed when the product was near equilibriu noisture contat. Data shows that overdrying hasbeen a cause practice. 82 8. Electronic sorting. Oosing of the nucilage greatly hinders the nachine feeding of ripe fruits for sorting. Crea areas on ripe fruits require a nachine that scans the fruit better. Sorting by shades is not a very effective way of separating the green fron the ripe fruits. FURTHER STUDIES Purther rebounding or resiliency studies for green and ripe coffee fruits. Pull needed to renove a ripe ad a green fruit fron the tree. Resistace to paetration of a sharp point (needlelike) in ripe ad green fruits. Sliding and rolling coefficients of friction. Drying studies. Perforation of the parchment previous to drying. Measure-cuts of inside tenperature of a coffee been exposed to direct sunlight. Effects of internitent drying periods. Surface water renoval studies. Use of solar energy for drying. Vacuun.drying studies. Respiration rate studies. Storage studies. Ripe fruits. 83 Pulped wet parcbent coffee. Partially dried ad dried parcl-ent coffee. Further electronic sorting studies. Studies on the effect of ethelene, 2-4D, or other growth regulators on the color of the coffee-fruit as a help in their sorting. Alvarez, A. 1., (1956). fluevo nhtodo de beneficiado del café. (New nethod of coffee processing). Ayer 6 (21): 4-5. Daron Gote, Y., and E. T. Pukunaga (1956). harvesting ad processing for top quality coffee. University of Hawaii Ext. Cir. 354. 20 pp. . I Barton, 1.. V. (1941-42). Relation of certain air tenperature ad huidities to viability of seeds. Boyce Thonpson Inst. Contrib. 12: 85-102. Barton, 1.. V. ad A. Goenga (1952). Electrical noisture neter for the deternination of noisture in coffee beas. Boyce Thonpson Inst. Contrib. 16:461-468. Barre, fl. J. ad 1.. 1.. Sonnet (1950). Parn structures. John Wiley ad Sons, flew York. Chapna ad Hall, Ltd., London. 650 pp. Biale, J. B. (1950). Post-harvest physiology ad biochenistry of fruits. Ann. Rev. of Plat Physiology 1: 183-206. Blasingsne, R. V., and A. Eschawald (1954). New coffee scrubber ad washer. Agr. Engr., 35: 326. Carbonell, R. (1953). Reconendaciones sobre el nuevo atodo de beneficiado de cafe nediate el uso de soda caustics y resultados con productos quinicos que ,aunenta su efectividad. (Recs-endations for the use of the new nethod of coffee processing by the use of caustic soda and results obtained with chenicals that increases its effectiveness.) Ministerio de Agricultrua y Gaaderia. Centre flacional de Agrononis. Sate Tecla, El Salvador, C. A. Carbonell, R., y 11. T. Vilaova (1952). Seneficio rapido y eficiente del cafe nediate el uso de soda caustica. (Past ad efficient coffee proc ssing by the use of caustic s .) Ministerio de Agriculture y Gander a. Centro National de Agron a. Sate Tesla, El Salvador, C. A., Boletin Tecnico No. 12. 85 Clark, A. , (1956). Solving a coffee hadling problen. Coffee ad Tea Industry 79:53. Claypool, 1.. L., ad R. 14. Keefer (1942). A clorinetric nethod for C02 deternination in respiration study. Proceedings of the Anerica Society for flort. Sci., 40: 177-191. Colana, D. A., ad 11. C. Pellows (1925). flygroscopic noisture of cereal grains, ad flax seed exposed to atnospheres of different relative huidity. Cereal chenistry, 2: 275-287. 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