THE INFLUENCE OF FORCED CONVECTION IN A ROASTING OVEN OF THE WEIGHT SHR‘INKAGE, FUEL CONSUMPTION AND COOKING TIME WHEN ROASTING BEE-F EDWARD FRANCIS MANEY. JR. SSSSSS IIIIIIIIIIIIIIIIIIIIIIIIIIHIIIIII 3 1293 O1 LIBRARY Michigan State University THE INFLUENCE OF FORCED CONVECTION IN A ROASTING OVEN OF THE WEIGHT SHRINKAOE, FUEL CONSUMPTION AND COOKING TIME WHEN ROASTING BEEF 3: Edvard Francie Haney, Jr. A THESIS Sub-itted to the School of Graduate Studies of Michigan State Univereity of Agriculture and Applied Science in partial fulfill-ent of the require-ente for the degree of MASTER OF ARTS' School of Hotel, Restaurant and Institutional Management 196# Approved by Chairman, Examining Connittee ACKNOWLEDGEMENTS The author wishes to eXpress his sincere thanks to Dr. J. Leon Newcomer, past Director of Food Service Industry Research Center. under whose careful guidance and unfailing interest this research study was undertaken. A He is also deeply indebted to Mr. Frank D. Borsenik, in- structor in the School of Hotel, Restaurant & Institutional Management, for his kind assistance and valuable help in check- ing and preparing the nethod and procedure used in undertaking this investigation and for guidance in preparation of the final draft. The writer greatly appreciates the financial support of the Schiltz Foundation as the basis for the Grand-in-Aid pro- vided by Michigan State University for the past year, which made it possible for hin to complete this project. ii was INFLUENCE or roncnp couvncrxon II A Roasrxnc oven or was errant SHRINKAGE, FUEL consunprxon AND COOKING TIME warn ROASTING BEEF 8! Edward Francis Haney, Jr. AN ABSTRACT Submitted to the School of Graduate Studies of Michigan State University of Agriculture and Applied science in partial fulfillment of the requirements for the degree of MASTER OF ARTS School of Hotel, Restaurant and Institutional Management 196“ Approved by Chairman, Examining Committee iii ABSTRACT Edward Francis Haney, Jr. There are three methods of heat transfer, conduction, convection. and radiation. Convection is predominant in con- vential roasting-baking ovens. However, there are two modes of convection, natural and forced. Ovens operate principally on the former. Engineers have recognised for a long time that the rate of heat transfer between the heat source and the object being heated is considerably increased under forced convection con- ditions. Within the food service industry, little work has been done in this area. Since theoretical considerations im- plies that utilization of the forced convection principle will influence the performance of ovens and the efficiency of roast- ing, the objective of thisstudy was to utilize forced convec- tion in a roasting oven and to measure the influence on the shrinkage, fuel consumption and cooking time when roasting beef. Control factors were determined by roasting beef under natural convection conditions at various oven temperatures. experimental data was then taken by cooking similar roasts under forced convection conditions at various oven temperatures and at various air velocities. The results show that forced convection in roasting-baking ovens does influence the weight shrinkage, fuel consumption and cooking time when roasting beef and that Optimum conditions iv prevailed in the region 275 degrees Fahrenheit oven tem- perature with an air velocity of 769 feet per minute. When the results achieved at this air velocity and temperature are compared with the results obtained in a conventional, natural convection oven found that there was on a) a decrease in b) a decrease in c) a decrease in d) a decrease in at 550 degrees Fahrenheit, it was an average: cooking time of 2.48 minutes per pound, volatile loss of 2.08 percent, drip loss of 3.15 percent, shrinkage of 5.2} percent, and e) an increase in fuel consumption of 0.17 kilowatt hours. CONTENTS INTRODUCTION REVIEW or LITERATURE STATEMENT OF THE PROBLEM OBJECTIVES APPARATUS PROCEDURE DATA AND RESULTS DISCUSSION OF RESULTS BIBLIOGRAPHY v1 PAGE 12 15' 2h LIST OF TABLES TABLE PAlE 1. Air Velocities at Various Pully'Combinations 21 2. Total Shrinkage, Volatile and Drip Loss -- 25 Cooking Time -- Oven Fuel Consumption of U.S. Choice Top Round Roasts at Various Temperatures Under Natural Convection 3. Total Shrinkage, Volatile and Drip Loss -- 29 Cooking Time -- Oven and Motor Fuel Consumption of U. 8. Choice Tap Round Roasts at Various Temperatures and at a Constant Air Velocity of 769 Feet Per Minute A. Comparison and Difference Between 350 Degrees 51 Fahrenheit Under Natural Convection and 275 Degrees Fahrenheit at an Air Velocity of 769 Feet Per Minute 5. Total Shrinkage, Volatile and Drip Loss -- 34 Cooking Time —- Oven and Motor Fuel Consumption of 0.8. Choice Top Round Roasts at Various Air Velocities with Temperature Constant at 275 Degrees Fahrenheit vii LIST or FIGURES EIGURE IO. 11. The Three Regions of—a TurbuIRnt Boundary Layer The Experimental Oven The Motor, Step-pulleys, Motor Shaft and Belt . The Anemometer The Roasting Pan, Wire Rack and Specimen The Electric Watt-Hour Meter, Clock and Switch Average Cooking Time in Minutes Per Pound; at Various Temperatures Under Natural Conf . vection and at an Air Velocity of 769 Feet Per Minute Average Cooking Time in Minutes Per Pound at Various Air Velocities and at a Cooking Temperature of 275 Degrees Fahrenheit Average Shrinkage, Volatile and Drip Loss at Various Temperatures Under Natural Con- vection and at an Air Velocity of 769 feet per minute Average Fuel Consumption of Oven at Various Temperatures Under Natural Convection and at an Air Velocity of 769 Feet per minute Average Shrinkage, Volatile and Drip Loss at' Various Air Velocities and at a Cooking Temperature of 275 Degrees Fahrenheit Average Fuel Consumption at Various Air Veloc- ities and at a Cooking Temperature of 275 De- grees Fahrenheit viii l6 17 18 19 26 30 32 35 36 INTRODUCTION There are three methods of heat transfer, conduction, convection and radiation. Conduction is the movement of heat from a warm body to a cooler body when the two bodies are in contact with each other. Convection is the transfer of heat between a moving fluid medium, such as gas, air or fat, and a heat surface. It is also the transfer of heat from one point to another within the fluid by movements within the fluid. Radiation is heat which passes from a higher tempera- ture without necessarily heating the space in between. Convection can occur by two methods, natural and forced. When a fluid, such as air, is heated, it expands. The heated portion rises while the cooler denser air moves downward. This is known as natural convection. If a mechanical apparatus, such as a fan or blower, is used to move this fluid then it is called forced convection. Natural convection is the condition under which a conven- tional roasting-baking oven common to the restaurant industry, whether gas, oil, coal or electrically heated, ordinarily Operates. These are heated enclosures wherein heat is transferred from the heat source to air which in turn heats the product. Newton's law of heating and cooling states that the rate of heat transfer is directly prOportional to the difference in temper- ature of the two substances. However, heat transfer is hindered ty 3 layer of stagnant air known as a laminar layer which surrounds 2 the object being heated; the greater the thickness of this layer, the longer it takes heat to transfer from the source to the object. In accordance with heat transfer laws the rate of heat trans- fer for the same temperature differential in greater under forced convection than under natural convection because forced convec- tion tends to reduce the laminar layer of air. Engineers have known this for a long time. However, prior to June 1960, there is relatively little evidence that work had been accomplished in applying principles of forced convection to conventional roasting- baking ovens.1 Since little work has been accomplished in this area and since that heat transfer rate can be increased by increasing the air velocity, the following hypothesakere made. (A) The cooking rate should increase with an increase in air velocities. There- fore, less cooking time should be required. (B) A reduction in cooking time should result in a corresponding reduction in fuel consumption. (C) At any given temperature, a reduction in cook- ing time should result in less shrinkage. The purpose of this study was to investigate the validity of these hypotheses. “- - p- - w --v- “-_- M ~¢ TThe research on this study was concluded June 1, 1460. REVIEW OF LITERATURE A search of literature pertaining to forced convection in the Food Service Industry shows a lack of writing in this area. It was, therefore, necessary to turn to the engineering profession for this information. Croft (3) Brown and Marco (2) Jacob (10) Manly (ll) Hender- son and Perry (9) Giedt (7) Worthing and Holliday (12) all point out that there are three different ways in which heat is trans- ferred; conduction, convection and radiation. However, Croft (3)-points out that the conveyance of heat from one body to an- other may occur simultaneously by any two or all three of these methods. A description of each of these methods follows. Conduction: Croft (3) and Brown and Marco (2) point out that there are two means by which conduction can occur. One is referred to as external conduction while the second is identified as internal conduction.' Croft (3) refers to external conduction as heat which is transmitted from the molecules of a warm body tothe molecules of cooler body when the two bodies are in contact with one anbther. Internal conduction, as Brown and Marco (2) state it, is heat that is transmitted from molecules in a.high temperature re- gion to molecules in a low temperature region within a homogeneous substance. This action is without discontinuity and with a continu- ous fall of temperature from the high to low region (i.e., the heat traveling from the outer surface of a roast toward the center of . I a roast.). A. Convection: Manly (ll) states if air or water, or any other gas or liquid’is in contact with a solid surface whose tempera- ture is relatively high, heat will pass by conduction from the warm surface into the air or water. While this is being accom- plished, the heated portions of the fluids tend to rise, because a change in density makes the heavier cooler portions fall and push the lighter ones upward. Motion of a fluid when heat causes a difference in density of different portions, and because of the resulting effect of this situation or changing state, is called convection. Convection, like conduction, as emphasized by Croft (3) and~ Brown and Marco (2) also has two major classifications, natural andlforced. Natural convection, Croft (3) points out, is the transfer of heat by the moving fluid medium and a surface within the fluid body. When a fluid, such as air is heated, it expands. Since this causes the density of the heated portion to become lower than the surrounding air, this heated portion will rise and be re- placed by a cooler mass of air. This mass, likewise becomes heat- ed and displaced. Continuous circulating currents are thus set \4p in the fluid. Ihen this movement of air is produced by mechan- ical means such as a fan or pump, Brown and Marco (2) refer to it as being transmitted1by forced convection. However, it must be remembered, as Jacob (10) points out, that heat convection without conduction does not occur. Convec- tion brings warmer parts of a fluid in contact with cooler ones, causing conduction. 5 Radiation: Brown and Marco (2) refer to heat which passes from a higher temperature body through space to bodies at lower temperatures some distance away without warming the medium in between, as being transferred by radiation. It Operates by vir- tue of electromagnetic wave motion essentially the same as that employed in a microwave oven, or the passage of the sun's heat to the earth. Resistaggg £2.§222 Transfer: Henderson and Perry (9) relate that the resistance to the heat ransfer principal is caused by a relatively stagnant layer and an adjacent turbulent zone of fluid at the solid-fluid interface. Conductance can be increased by re— ducing the thickness of the laminar layer of fluid by more agita— tion than is present in natural convection alone. This solid fluid interface is shown diagrammatically in Figure l, Page 6, where the flow of air over a surface is divixed into three regions. In a very thin layer of air near the nail (O to A), viscous forces predominate and the fluid layer is lami- nar. Next to this layer is a region in which the motion is either streamlined or turbulent at any instant (A to B); it serves as a transition region or buffer layer between the laminar sublayer and the fully develOped turbulent region (above B). Brown and Marco (2) further emphasize that at very low veloc— -ties and at a constant temperature each particle of the fluid moves in a path substantially parallel to the path foLlowed by all otner particles, and the flow is described as laminar. This does not mean that each particle moves at the same velocity as 6 every other particle but simply that all particles travel in parallel directional paths. When the flow of the fluid is increased leyond a certain critical velocity, laminar flow can no longer continue and turbulent flow predominates. In the range of turbulent flow innumerable eddy and cross currents occur. l .//_fi \ l @7 ' “ - //’ ‘ ’ /' . “ Turbulent I’F hj:::;,ri 7’ \\ ’::\\) L t i. " \ ' .z ‘\ h l -. ‘,V f“ “81°“ k :4 ., 2:7“‘\<':‘\ \q,’ \ \ ~ ,’ \ 3 ~. ( ' \ 7, ‘ / '\ ‘\/’ “ \ ‘ \u_r \ / 3 ea / A ’) 2 "”‘\"‘ \k ' 7 ,2s5 / '—,—-'- _--'.‘ v’f"'llr"‘ff/T~’f*“—H‘ "‘ '7" “"*,“" ’1/ Transition /./ I '/ I Q-/’ ,"/-\\ \\ ,//7\;f* , » (J, x ,. : Region . ”/1 / k-/ fr/‘w-M‘” ‘\..__\ "F ~ V " I // -/ ,-/ //\ f" x x * ‘-\ \~ ,v/ ’/S) ' ‘ l >A_-’ ‘ “"2. 52'. .:‘ ______ '_ £’/_: _ '_i:t;r::';f"1 - _. .;:’/ '_ _’ - _ A Laminar E::?{53’v/f"‘ :-‘*":1:f7jfl' ” ”-:--€;—g;‘_ lam—M- R9810! "”5 Z- -' “_ '_w ;::;:;;;_aa* '" i_“_ :7§;() Figure 1. THE THREE REGIONS OF A TURBULENT ' BOUNDARY LAYER Giedt (7) This critical velocity for any temperature-velocity combina- tion may result in a peculiarity occurring in the slepe of the curve. In this instance, rather than the temperature being con- stant and the velocity being the variable, the opposite is true-— the temperature is the variable and the velocity is the constant. The transition that occurs at the critical velocity from streamlined to turbulent flow is neither instantaneous nor posi- tively fixed. As a result there is an appreciable overlapping 7 of the highest velocity for laminar (streamlined) flow and the lowest velocity at which turbulent flow may occur. No attempt is ordinarily made to measure the thickness of this laminar film. The film may be immeasurably thin or several hundredths of an inch in thickness, but in the study of heat trans- fer it may be visualized as a barrier to the flow of heat. Although conductance can be increased by reducing the thick- ness of the laminar film, Dersch (5) relates that heat transfer by forced air convection decreases as the diameter of the item around which the air flows is increased. Therefore, the smaller the product, within certain limitations, the greater the heat trans- fer achieved. Dersch (5) further states that heat transfer by forced convection is 7.5 to 19.6 per cent higher for curved sur- faces than for plane surfaces; 8 per chat less for items inclined #5 degrees; and increases as the surfaces roughness increases. Henderson and Perry (9) also add that the amount of turbu- lence decreases as the distance from the fan is increased and will also vary depending on the viscosity of the fluid. Further restrictions that will alter the cooking time re- quired are pointed out by Dawson, Linton, Earkin and Miller (h). These factors are: (a) cooking methods, (b) Juiciness as related to fat content, (6) internal temperature to which the meat is cooked, (d) time cooked in an uncovered pan, (e) shape and thickness of the roast, and (f) the grade of the meat. Pitch and Francis (6) mention that the amount of connective tissue and the length of aging will also effect the cooking time, as will the composition of the meat and the temperature of the roast 3 at.the beginning of the cooking period. In addition, Lowe (ll) emphasizes that the following factors will affect the time required to cook meat; (a) the cooking temper- ature; and (b) weight, surface area, and the shortest distance to the thickest portion of the meat. In the area Of food service, Dersch (5) mentions that the bak- ing industry was the first to utilize forced convection by employ- ing steam Jets in a tunnel oven for the sole purpose of creating air turbulence within the baking chamber. About fifteen years ago, the first duct-type agitator made its appearance. The fans in these agitators would discharge from 1500 to 2000 cubic feet of air per minute at localized spots in the oven. However, little effect was realized. The next attempt to provide agitation took the form of a series of centrifugal blowers driven by an external motor. If noth- ing else, these wheels served to give good lateral distribution of temperature. However, Lough (11) in his Q3331 gf the Effect 2; Air Velocity and Temperature 23 ngrosting Ground figs; found forced convection definitely increased the defrosting rate. An Optimum velocity for his study was found to be between 350 and 400 feet per minute. Nothing appeared again in literature until Hampel (8) mentions that the Research Engineer Laboratories of the American Gas Associa- tion, Incorporated, had been experimenting with forced convection since 1955. In May, 1959, the results of this research “ere par- tially responsible for the introduction of a gas-Operated, forced convect on oven sold under the trademark of the Wimco Oven. During this same period preliminary work in the use of forced 9 convection was conducted by Borsenik and Newcomer (l) of the Food Service Industry Research Center at Michigan State University, East Lansing, Michigan. Meat loaves were used as the specimen in their experimentation. The results indicated that under forced convection total cooking time at 350 degrees Fahrenheit was 66.9 minutes, while under natural convection 107 minutes were reyuired. Fuel consumption at this temperature was 1.0 kilowatt-hours for forced convection whereas for natural convection it was 1.} kilo- watt-hours. An even greater reduction in fuel consumption was ex- perienced when the temperature under forced convection was drOpped to 250 degrees Fahrenheit; this was found to be 0.7 kilowatt-hours or 48 percent less than at 350 degrees Fahrenheit. Considering this drop in temperature, cooking time still remained substan- tially the same when compared to the time required at 350 degrees under natural convection. Forced convection also was found to in- fluence shrinkage. Under natural convection it was reported to be 22.3 percent while under forced convection it was found to be 21.6 percent. Dersch (5) states that there has been much discussion about forced versus natural convection as a method of heat distribution in roasting-baking ovens. About the only point of general agree- ment is that air agitation is influencial. Ebwever, there has been little agreement on the extent of agitation (i.e., flow rate) and the influence on fuel consumption, shrinkage and cooking rate. In the use of forced convection, Dersch (5) also mentions that for any given temperature there is a correspondingly Optimum volume of air which will transfer the maximum amount of Btu's from 10 the heat source to the product. Increasing the volume of air be- yond this point will not increase the transfer of heat. STATEMENT OF THE PROBLEM From an engineering standpoint, it is realized that the rate of heat transfer for the same temperature differential is greater under forced convection than under natural convection. Literature pertaining to this subject shows that this area has not been fully investigated in its application to roasting- baking ovens. ll OBJECTIVES The Object of this study is to measure the influence of forced convection in a roasting oven on weight shrinkage, fuel consumption and cooking time when roasting beef. 12 APPARATUS The Experimental 9133: As shown in Figure 2, Page 16, the oven used in this study was a conventional, electrically- heated oven modified by the addition of an electric, motor-‘ driven fan. The apparatus consists of an enclosure (A) with internal demensions of 26% inches long, 18% inches wide and 14% inches high. Heat was provided by two heating elements (8) located at the base and running horizontally along the side walls with an electrical rating of 115 volts and 1600 watts. A 10-inch, 3-blade, propeller-type fan (C) around which a shroud (D) 13—inch in diameter and 6-inches wide was secured. was mounted on a shaft driven by a % horsepower, 1725 R.P.M. motor (E) Figure 3, Page 17. Four, h-step pulleys (F) were affixed to the motor shaft and the fan shaft which were driven by a ”v" belt (6). Measurement 31 Air Velocity: The Velocity of air was measured with a Davis Instrument Manufacturing Company Anemom- eter, Figure 4, Page 18, for different combinations of the step pulleys. The results are shown in Table l, Page 21. Velocities ranging from 350 feet per minute to 2500 feet per minute were recorded at one foot from the fan blade. :23 Roasting Pan: All roasts were prepared in a stainless steel pan, Figure 5, Page 19, 16 inches long, ll-inches wide 1nd l-inch deep. Roasts were placed in the pan on a wire rack approx~ imately one half inch from the base. This permitted more surface 1h area exposure to the flow of air and also aided in the collection of drip loss. Recording 25 Temperatures: Temperatures were measured in three regions: the oven temperature, the surface temperature of the roast, and in the center of the roast. Thermocouples were placed in each of these areas while the opposite ends were con- nected to a Minneapolis-Honeywell, Brown Electronic, Potentiometer, which indicated and recorded temperatures. The accuracy of this instrument is within plus or minus four degrees Fahrenheit over the 0 to 600 Fahrenheit degree range and within plus or minus one degree Fahrenheit between room temperature and #00 degrees Fahren- heit. The temperature settings of thermostat dials of commercials ovens often do not agree with the actual temperature in the oven. Consequently, oven temperatures were manually controlled and the actual oven temperatures were recorded on the potentiometer. Measurement 2; 2231 Consumption: Total fuel consumption was determined by ascertaining both the quantity of electrical power to the motor at different speeds and the quantity of electrical power to the oven. Figure 6, Page 20, shows the electric watt- hour meter (8), which indicates, by the speed of the disk, the electrical load. Electric power to the heating elements was determined by correlating the speed of the watt-hour disk with the oven in Opera- tion against the speed of this disk using a 2000 watt light bank. Figure 6, Page ZO‘also shows a clock (I) controlled by a tripswitch (J) which automatically measure the time the heat elements received 15 electrical power. By measuring the power consumption rate and the total time the power was applied, the total power consump- tion could be calculated. 16 l ! -~*, ::?§$ ,rt&w=\\ ‘8' ‘3) .. W .7 3 : a 5) "In 'hll; '. . I ' ,. \\. sea. ‘ ‘ Figure 2. The experimental oven 17 Figure 3. The motor, step-pulleys, shaft and belt 18 a.u- “'"- Figure 4. The anemometer l9 Figure 5. The roasting pan, wire rack and specimen Figure 6. The electric watt-hour meter, clock and switch 2l .ovan me“ on» use hoop ne>o on» meesuen has gas: sapwood neuelomocs on» an nonwaueuoa. omém 0.003 0mm. com ..o.~ ..o.m Om. um. 0.80N CON. 034 :OoN :O.+~ om.wH m.¢n4a haw. 00: :o.n :o.: -.ma o.nnnH ooh. 00: :m.~ :n.n 55.0 o.mwn 00m. 00m :m.n :m.m is n32. owm. com ..o.: _.o.n on.m 0.00h 00¢. CON :0.: :o.m 00.: 0.0mm 05m. 00m :o.m :o.m usom euwmdx sounds: . ueem nebdha ueawua sea «I. ma ma we we eeaut aeeh slay eoleueaa heuewdda seas-dam ee«u«uoaemlmmd . add Mo umelebor . menam Hflwmmm anodeeddnloo heaaaa osoaue» as eeaaaunnep aw< .H cane“ PROCEDURE Two major steps, preparation of the roast and roasting under conditions of natural convection, were necessary in determining the effect forced convection would have on the shrinkage, fuel con- sumption and cooking time of roasted beef. Determination of an Optimum air velocity and an Optimum cooking temperature resulted from an analysis of the information under conditions of forced con- vection. Preparation 2; Roasts: All specimens were 0.8. Choice, un- frozen, six-pound, paired, tOp round roasts. All roasts were re- frigerated overnight at 33 to 35 degrees Fahrenheit for no longer than 2# hours. This was done to insure approximately the same center temperature at the beginning of the roasting period. As near as possible, consistency in size and shape were achieved by trimming all paired roasts to five pounds. The weight of each roast was recorded to within one-eighth ounce on a Toledo Scale, Model #OBl-V. Although the grade and cut of meat were controlled, the amount of connective tissue, composition, length of aging and juici- ness as related to fat content could not be controlled. - Prior to roasting, recordings were made of the weight, center temperature and surface temperature of the product and the combined weight of the pan and wire rack. A thermocouple was inserted into the center of the roast and attached to the surface of the roast. The roasts were then placed 22 23 on a rack, in a pan, as shown in Figure 5, page 19, and inserted into the oven half way between the face of the fan and the oven door with the vertical side of each roast nearest the fan. When a center temperature of a 160 degrees Fahrenheit was obtained on all roasts recordings were made of the cooking time, finished weight and fuel consumption. Since the beginning weight of each roast was known it was possible to ascertain the drip loss by removing the roast and rack from the pan and weighing the liquid in the pan. Volatile loss was calculated as the difference be- tween the weight of the raw roast and the cooked weight of the roast plus the drippings. This study included fifteen roasting tests with two replica- tions of each test. One exception occurred where only one replica- tion was used. Roasting Eggs; Natural Convection: The results under natural convection conditions were used as a control. Three roasts, cook- ed separately, were roasted at temperatures of 200, 250, 275, 300 and 350 degrees Fahrenheit to a center temperature of 160 degrees Fahrenheit. An exception occurred in the case of those roasts cooked at 200 degrees Fahrenheit. Determinatigg‘gg‘gg thimum Velocity: Air velocities of 350, 500, 769, 1333 and 2000 feet per minute were selected from vel- ocities ranging from 350 to 2500 feet per minute (Table 1, page 21). These velocities were tested to determine if an optimum velocity fell within this range. Three roasts were again cooked at each of these velocities. DATA AND RESULTS Table 2, page 25, presents the control data; an analysis of the results when beef is roasted by natural conveccion. In the formulation of this data three roasts were cooked at each of the following temperatures: 200, 250, 300, 350 and #00 degrees Fahrenheit. All roasts were cooked to a center temperature of 160 degrees Fahrenheit except those roasts cooked at 200 degrees Fahrenheit where only a center temperature of 156 degrees Fahren- heit could be achieved; thus the reason for the notation Vincomplete". The time-temperature relationship of roasting beef under natural convection, as shown in Figure 7, page 26, shows a sharp decrease in required cooking time between the 200 to 300 degrees Fahrenheit cooking range. Viewing these points as a continuous curve rather than as lines from point to point, the curve remains substantially vertical between 200 degrees to 275 degrees Fahrenheit. 'Between 275 degrees and 400 degrees Fahrenheit the curve is more horizontal in nature. It was then decided to use 275 degrees as' the constant temperature. In viewing this time-temperature relationship it will be noted that under forced convection a peculiarity in the slepe of the curve appeared between 275 degrees and 300 degrees Fahrenheit. This may be due to what Brown and Marco (2) refer to as the "criti- cal velocity" for any given temperature-velocity combination. Figure 8, page 27, shows.the relationship.between air veloc- ities of 350, 500, 769, 1533 and 2000 feet per minute, and cooking at 25 euefiaaooma. sa.m os.m m .mm c as. m tweet.“ mm.m oo.N .mm :m. m : m:.m 5H.m wa.mm mo.mm : mm.m sm.: wa.mm . oo.Hm 00: thW NN.m mm.ma HO.Nm emmac>m om.m w~.e N .om oo.ww : mm.m om.o Ab.nH om.mn : so.m ma.o Hm.ma n~.on own nm.~ MMDM nn.mH OO.N emmuobm Nm.a ma.w mw.ma 0:.w: : :m.~ mo.n wn.wa 00.0: : sm.H sm.w wn.m~ om.m: com .a 60.5 $0. H .o emmue>s o .H mm.N ~a.ma mmuoo = HH.~ .¢N.w om.wa wb.aw : mm.a mm.u n:.o~ Hm.mw z Hm.a sm.o ¢m.ma 0:.mm 0mm ”an“ mannw ”WNW WMHWM OMHWMM ensueem os.~ mm.:~ ~a.o Ho.sa mm.aaa cow. Amsuv Amv Amv any Assassqsv Au.v soauamsenou ememmdumm eeoa seoa mason oususueaIeB Hana snoop anus .aaneaos cos seas se>o umdmooo noauoermou assays: secs: eehsusseamou escape» as nausea mason no» eoaono .m.p no noauamsenoo Hen» se>o :- old» madmooo nu eeoa make one eadusaos .emsmdauns «suck .N canes 125 l20 115 110 Cooking time in minutes per pound 105 100. 95 90 O‘ O’\ \l \1 CD 00 O U! 0 \fl 0 \fl ‘1-_"‘ 1"‘" T * W W 50 1+5 1.0 35 3O 25 O 26 r Figure 7. Average cooking time in minutes F per pound at various temperatures under c natural convection and at an air velocity p \ of 769 feet per minute \ F \ f (+- a \ latural convection T s Forced convection ) L,J” l. .i 4__*-l 1 L l l 1 1 J 200 220 2&0 260 280 300 320 3&0 360 380 ‘(00 Oven temperature in degrees Fahrenheit 27 eased! sea poem ma hudooaeb uw< ooow 83 8mm 82. 83 83 8.: 83 08a .82 83:03 0838s 03 can 8.. con 08 03 fiii.fi- -m a _ .fii 3m: :fl:3 4 a _ a -.m a- 2% -IA;.141 aaennohnsh assumes muw no easueuoaleu usdmooo s as use eeauaooae> ads esoaas> as mason sea seassdm as eldu wuamooo ensue>< .m shaman JIJ .11 - 0 mm mw on mm an mm mm 0.. me a: o: m: Om Cooking time in minutes per pound 28 time while holding the Oven temperature constant at 275 degrees Fahrenheit. Here again a sharp decrease in cooking time is evi- dent from 0 to 769 feet per minute. Beyond this point the cook- ing time is reduced but at a decreased rate; thus the reason for using 769 feet per minute as the Optimum air velocity. The temperatures Observed under forced convection at 769 feet per minute ranged from 200 degrees Fahrenheit to 350 degrees Fahrenheit. Sufficient charring Of the surface Of the roast occurred at 350 degrees to warrant terminating the work at this temperature. Observation of the data relating to total shrinkage, volatile and drip loss, as indicated in Table 2, page 25, and Table 5, page 29, shows that these factors are at their lowest when the meat was roasted under forced convection at 275 degrees Fahren- heit. Figure 9, page 50, presents this information in graphic ' form. Using cooking time as a means of comparison it can be noted that, given a constant cooking time, the same results would be achieved by roasting at 275 degrees Fahrenheit and an air velocity of 769 feet per minute as achieved when roasting at 590 degrees Fahrenheit under natural convection. Similarly, 263 degrees Fahren- heit at the same air velocity is equivalent to roasting at 350 degrees Fahrenheit under natural convection. Beyond this tempera- ture percent-loss tends to increase rapidly. At 350 degrees Fahren- heit forced convection volatile-loss is 7.55 percent greater and shrinkage is 5.57 percent greater than roasts cooked at the same temperature under natural convection. Table 5. Total shrinkage, volatile and drip loss - cooking time - oven and motor fuel Consumption of 0.5. choice top round roasts at various temperatures and at a constant air velocity of 769 feet per minute Total Fuel Motor Fuel Oven Fuel Consumption Consumption Consumption Total Shrinkage (S) Drip loss (%) Volatile Time per Temperature (IVE) (KWH) (Kan) pound loss (i) (minutes) ('F) 29 rwo o<3a>o~ O 0 O O rxwuvru MMOH \OB-f H.4r4rq o-ecocx 4-wx vn O O O H.4r4 22.}# 23.76 as 18 21.51 (DC) 0 HM O O O O muururu :- .¢.4 NR a O O O . O‘H H‘Vr4r4 o<3<>o~ \o\oao '0 O O O xxo- cu «no 0 to s u 8 -° = - b In s a sage O O o‘n r1 N¢Vr4nl «DQNH NO‘HI 0 es n“ °8 R .1 2.0a 2.96 k.22 3-07 c~creh pvwearq c3c>0rn nuncucx O O O C txu>o xxxx um e m: C u 56 s : : p n: s IAN 22.66 17.20 20.62 14.2k 1 .l6 1 29.k0 30.20 2 275 H \OU‘MO 0 -|O’\ n e H e HHH .00 19.75 29.53 30.60 50.h0 2. average 300 2.75 2.69 2.22 2. 9 ChGDJ’O nuwh 0 O 0 O ruaaox mmflo O O C O H.4run: «Lacocb 4’0—0-4 O I O O wno c» fiJfllV¢V a»: cu 4-mx .4 O O O O ¢\WL:|A NNNN 31.20 28 O 20 26.80 2 0‘0 average .72 5.06 “.22 %% 28.hh 27.0# 22.32 350 32-50 31.26 N 2 .82 30-53 .10 0 2 average Percent of weight loss 30 #0 _ Figure 9. Average shrinkage, volatile and drip loss at various temperatures under natural con— 38 vection and at an air velocity of 769 feet per 36 b minute 35} 32 _ 1h 12 10 _.drip A --------------------------------------------- 3//\/\ LAV’ 1 1 11 1 1 1 AiL 1 1 1 _J O '200 220 250 260 280 300 320 3‘0 360 380 #00 Oven temperature in degrees Fahrenheit a - indicates natural convection B - indicates forced convection. 31 Since roasting in a normal oven is usually accomplished at 350 degrees, and the forced convection data indicates an optimum cooking temperature at 275 degrees, a comparison of losses at these two temperatures produced the following results. Table 4. Comparison and difference between 350 degrees Fahrenheit under natural convection and 275 degrees Fahrenheit at an air velocity of 769 feet per minute 250’! '2222! Difference Cooking time in mine. per pound 32.01 29.53 2.h8 Drip loss % 6.22 3.07 3.15 Volatile loss.“ 18.75 16.67 2.08 Shrink loss S 2#.96 19.75 5.23 Fuel consumption 2.18 2.35 .17 in KWH In every instance, with the exception of fuel consumption, savings can be achieved by cooking at 275 degrees under forced con- vection as compared with natural convection at 350 degrees Fahren- heit. Figure 10, page 32, is a graph of the fuel consumption. Total consumption was determined by the summation of both the oven and motor fuel consumption. Again, fuel consumption is at a minimum at 275 degrees Fahrenheit. Table 2, page 25, presents a break- down of fuel consumption for the oven at various temperatures, while Table 3, page 29, shows fuel consumption of the oven and motor at a constant air velocity of 769 feet per minute. Kilowatt hours \,\.l W T 3.4 L— 5-5 “ 3.2 1- \14 p... T.__. \N O N \D N (I) f "—T—T""T—"—T' ” ’1 -4 “T'fi F.) s N 0‘ \I f.) N r.) e s e W # U'l T 2.2‘ 201 "" 32 Figure 10. Average fuel consumption of oven at various temperatures under natural convection and at an air velocity of 769 feet per minute Forced Convection / Natural Convection 1 1 1 1 --.- i J -1.___1_..__-1--._.1..TJ 200 220 2.0 260 280 300 320 MO 360 380 00 Oven temperature in degrees Fahrenheit 33 Total shrinkage, volatile and drip loss also support the statement that 769 feet per minute is an optimum velocity for it was at this velocity where the greatest savings were achieved. Table 5, page 3“, and Figure 11, page 35, show the results of these tests. Here again it will be noted that a decrease is evi- dent up to 769 feet per minute. From there on, the curve reverses its slope and the cptimum velocity has been achieved. Fuel consumption of any temperature studied was at a minimum at 275 degrees Fahrenheit and at an air velocity of 769 feet per minute. Figure 12, page 36, and Table 5, page 3“, present the data which shows a separate consumption for both the motor and oven. Only in one instance was greater savings achieved at an air velocity other than 769 feet per minute and this was at 2000 feet per minute. However, the fuel consumption of the motor in- creased to such an extent that this lower consumption has little effect on the combined motor-oven fuel consumption as is also shown in Figure 12, page 36. 3h oo.n .H a wD.mw . Hm.bw . oneness mm.~ m .H N .H 4~.:~ m4.m ms.ma 0. ~ = mo.m s:.H nn.a ms.m~ ma.m oo.om :.mm = mo.» ~$.H om.a oo.ma ~m.~ ma.mm w.mm ooom ss.~ H .H o. s .nm ~.m mH.om m. m omen... mo.w ww.s o.H w:.w~ mm.“ mH.~m o.m : mm.m mo.a am. ms.nm :H.m No.0m 0.5m : mo.~ oo.m mm. om.:m m:.n 0:.Hm m.mm : :n.m mm.” mm. os.m~ mo.: no.4s 0.4m : oo.m mm.H so. om.:~ nw.H sm.- n.0n mans nn.m mm.s a. ms.o~ so.n sm.ma m.m~ aweso>u m~.~ Hm.s mma m~.mH -.: ofl.us o.m~ = om.m ~m.~ ms. o~.sH om.m :~.:H ~.on : o¢.~ mw.H ms. mo.- :o.~ mm.o~ a.m~ mos ~n.m .H . nn.- mm.n om.ma m.nm omen... so.w .H mma mw.mm ~m. mm.oa o.¢ : on.m «0.4 as. mo.:m ~m.s ,cm.oH :.sn = sm.~ m:.~ ms. os.ms m:.m :m.:~ m.am : mm.m ms.H no. ma.nm as.n wn.m~ o.:n 00m mm.m mm.H . mn.mm sm.m mo.om . m .mauope m:.m Ho.H mmq mm.om o . ma.wm w.m = ::.m mm.4 mm. oo.mm oo.oH oo.wa o.an z no.m am.s as. mo.:m aw.n a¢.wa :.mm on« Anzac amass lupus Ans Ans lav Aeouanaxc A.»=aae cos soaunlnncoo cofiunmnsuoo sodunlnsnoo smsmndnmm ssoa smog vmnom «sens H.5a H.5a ass» Hence aauo .Haueaos u.a .sae auaoofl.> deuce nouox mono . bndmooo ufl< uuemcsansh seekhec mum as ussusnoo eunusuenleu mafia sodudooaeb has snoauss as cocoon visas moo sodomo .m.p no ooaaassauoo Hush nonol nus aeno 1: old» Uddlooo :1 wsoH mans nos cadusao> .emsmdwuns asuOh .u sans“ Percent of loss 22*- 20+- 18'- 16- U 35 figure 11. Average shrinkage, volatile and drip loss at various air velocities and at a cooking temperature of 275 degrees Fahrenheit \\ J, shrinkage \ \\ , / ”_ __ volatile -1. . l 1-1-1- 1.1--1 1 -1 -l__.__l (-00 not 600 800 10001200 1400 16001800 2. 00 Air velocity in feet per minute Kilowatt hours 56 Figure 12. Average fuel consumption at various air velocities and at a cooking temperature of 275 degrees Fahrenheit combined ,” motor . _ 1 l. _ J. 1 L L 1 i _ ._. 0 2-1 1.00 600 800 1000 1200 11400 1600 18m 2000 Air velocity in feet per minute DISCUSSION OF RESULTS The results reported herein indicate that forced convection in roasting ovens can influence the weight shrinkage, fuel con— sumption and cooking time when roasting beef. Forced convection cooking consists of the movement of air being mechanically moved across and around the surface of the roast. Various air veloc- ities were obtained by utilizing a belt attached to step-pulleys which were driven by an external motor. These velocities ranged from 350 feet per minute to 2000 feet per minute. An Optimum air velocity, at a constant temperature of 275 degrees Fahrenheit, was observed in the area of 769 feet per minute. Information bearing out this statement consisted of evaluating the collected data on the points of the lowest fuel consumption, the least amount of shrinkage and the last area where cooking time was substantially reduced. When the results achieved at this air velocity of 769 feet per minute and at an oven temperature of 275 degrees Fahrenheit are compared with the results obtained in a normal, conventional, natural convection oven at 350 degrees Fahrenheit, it was found that there was on the average: a) a decrease in cooking time of 2.#8 minutes per pound, b) a decrease in volatile loss of 2.08 per cent, c) a decrease in drip loss of 3.15 percent, d) a decrease in shrinkage of 5.23 percent, and e) an increase in fuel consumption of 0.17 kilowatt-hours. 37 10. 11. 12. 13. 1h. BIBLIOJRAPHY Borsenik, Frank D., and J.L. Newcomer."Experimental Oven Ups Speed, Lower Fuel Consumption," Institutions Magazine, November, 1959. 12. Brown, A.J., and Marco, S.M. Introduction to Heat Transfer. New York: McGraw-Hill Book Company, Inc., 1951. Croft, T. Practical Beat. New York: McGraw-Hill Book Com- pany, Inc., 1939. Dawson, E.H., Linton, G. S., Harkin, A. M., and Miller, C. Factors Influencing the Palatability, Vitamin antegt and Yield of Cooked Beef. Home Economics Research Report Number 9. Prepared by the United States Department of Agriculture, October, 1959. Dersch, John A. "Principles of Heat Distribution in Baking Ovens," ggkgris DigestI XXXII (October, 1958), 66 Fitch, Natalie 3., and Francis, C.A. Foods and Principles of Cookery. New York: Prentice-Ball, Inc.,.19h8. Giedt, W.B. Beat Transfgr. Princeton, New Jersey: D.Van Nostrand Company, Inc., 1957. Hampel, T.E. "Letters," Institutions Magazine, January, 1960, 18. >Henderson, S.M., and Perry, R.L. égr icultural Process gngingegigg. New York: John Y'iley and Sons, Inc., 1955- Jacob, u. Taggt Trgngfgr, I, New York: John Wiley and Sons, 1110. ' 19‘59e ‘Laugh, John, Jr. "A Study of the Effect of Air Velocity and Temperature on Defrosting Ground Beef". Unpublished Master's thesis, School of Hotel, Restaurant and Institutional Management, Michigan State University,1958. Lowe, Belle. Experimental Cooke_y. 3rd ed. New York: John Wiley and Sons, Inc., l9h3. Manly, H. P. Heat Cooling and Air Conditioning Handbook. Chicago: Fredrick J. Drake and Company, 19h7. Worthing, A.C., and Halliday, D. Heat. New York: John Ailey and Sons, Inc., l9h8. 38 R0011 USE 01:11.1 ROOM 0.1.: 0:111! . - __ ' ““P‘W w? "I“ {3 «W . . - .3 a?» can .30 a, kk/‘l HICHIGQN STQTE UNIV. LIBRRRIES lllllIWIWill!WWIIllllllllIlllllllllllllllHIIIIIWHI 31293015914579