_——— _—'-‘— _—_———- ___—————- f __———I—' ’— ——-——-—— —"—— _—_———— #— _———-—'- _——-——‘ —_—-——— #— FACTORS AFFECTING ICE CREAM PACKAGiNG Thesis for the Degree of M. S. MICWGAN STATE COLLEGE Donald Anton Seifert 1951 I u.‘ '—.*‘~. r.‘ ‘ . \ ' ' ’t:l‘.€~’“'- .“ O . "n‘ ‘ "NJ . ,‘D- . 130/,“ >09" a"; MSU ' AUG 2 5 2014 '(J3 1 1 1 4 RETURNING MATERIALS: P1ace in book”drop to remove this checkout from your record. FINES willl be charged if book is returned after the date stamped be10w. FACTORS AFFECTING ICE CREAM PACKAGING BY DONALD ANTON SEIFERT w A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Dairy 1951 THESIS ACKNOWLEDGMENTS The writer wishes to express his sincere appreciation to the following: Dr. Earl Weaver, Professor and Head of the Depart— ment of Dairy, for placing the facilities of the department at the writer's disposal; Dr. J. A. Meiser, Assistant Professor of Dairy, under whose direction this work was done, for his helpful suggestions and constructive criticism throughout the course of this inves— tigation, and for his invaluable assistance in the preparation of this manuscript; Mr. J. M. Jensen, Assistant Professor of Dairy, who judged the many samples of ice cream for flavor score and body and texture score. r'm-Jo ‘3;_32:.s.': ‘ ‘2 b d J; TABLE OF CONTENTS Page INTRODUCTION . . . . . . . . . . . . . . 1 REVIEW OF LITERATURE . . . . . . . . . . 3 Evidence of Moisture Loss in Packaged Foods . . 3 Cheese . . . . . . . . . . . . . . . 3 Butter . . . . . . . . . . . . . . . 5 Ice Cream . . . . . . . . . . . . . . 7 Meat . . . . . . . . . . . . . . . . 8 Various Frozen Foods . . . . . . . . . 9 Moisture Loss Mechanisms . . . . . . . . . 12 Initial Loss During Hardening . . . . . . . 13 Total Volumes . . . . . . . . . . . . l3 Diffusion . . . . . . . . . . . . . . l4 Sorption With Subsequent Evaporation . . . . 15 Factors Affecting Evaporation in Packaged Products . . . . . . . . . . . . . . 16 Length of Storage . . . . . . . . . . . 16 Temperature of Storage . . . . . . . . . l7 Circulation of Air . . . . . . . . . . . l9 State of Moisture Humidity Surface Coating on the Product Vapor Pressure Differences Packaging........... Surface Area . . . . . . . . Thiclmess of Packaging Material . . . Heat Transfer . . . . . . . . . Closure Seal . . . . . . . . . . Packaging Material . . . . . . . . Physical and Chemical Effects of Moisture Loss Flavor Deterioration Surface Films . . . . . . . . . Shrinkage PLAN OF EXPERIMENT . . . . . . . . GENERAL PROCEDURES . . . . . Composition of the Mix . . . . . . . Mix Ingredients . . . . . . . . . . Freezing and Packaging . . . . . . Producing Shrinkage . . . . . . . . iv Page 20 21 23 25 26 26 27 28 28 29 31 31 32 32 34 36 36 36 37 38 Page Measurement of Moisture Loss . . . . . . . 38 EXPERIMENTAL . . . . . . . . . . . . . 40 Plastic Containers . . . . . . . . . . . . 40 EffectofLids............. 43 Position of Paraffin . . . . . . . . . . . 45 Saturation . . . . . . . . . . . . . . . 49 Temperature . . . . . . . . . . . . . . 53 Peel Test . . . . . . . . . . . . . . . 55 Shrinkage . . . . . . . . . . . . . . . 56 Preliminary Moisture Determination . . . . . . 62 Moisture, Flavor, and Body and Texture Deterioration . . . . . . . . . . . . . 67 DISCUSSION . . . . . . . . . . . . . . . 74 SUMMARY AND CONCLUSIONS . . . . . . . . 81 LITERATURECITED............ 83 LIST OF TABLES TABLE Page I. Weight Changes in Various Ice Cream Packages Stored at Two Temperatures . . 54 II. Amounts of Ice Cream Adhering to Various Containers . . . . . . . . . 57 III. Preliminary Determination of Moisture Loss and Quality Deterioration . . . . 65 IV. Determination of Moisture Loss and Quality DeteriOration (Mix 1) . . . . . 70 V. Determination of Moisture Loss and Quality Deterioration (Mix 2) . . . . . 71 LIST OF FIGURES FIGURE 1 Page 1. Effect of rigid plastic containers on weight losses of ice cream at cab— inet temperature . . . . . . . . . . 41 2. Effect of container lids on weight losses of ice cream at cabinet temperature . . . 44 3. Effect of position of paraffining on weight losses of ice cream at cabinet temper- ature..............47 4. Effect of saturation of carton on weight losses of ice cream at cabinet temperature............ 51 5. Comparison of air loss and moisture loss of ice cream in plastic coated containers............59 6. Positions of sampling . . . . . . . . . 64 INTRODUCTION Packaging was intended originally as a means of trans— porting food products from the producer to the consumer irre— spective of the container's influence upon the quality of the product. Today we are conscious of the fact that packaging must maintain the fresh wholesome appearance of packaged foods during the normal interval that follows manufacture and precedes consumer consumption. With our present extended periods of storage, this problem of maintaining natural flavor and appearance has become more and more troublesome. Evidence of moisture loss and flavor deterioration in packaged dairy products may be found in the literature; how- ever, much of this information is restricted to butter and cheese. More recent investigations of a preliminary nature have shown that packaged ice cream will lose moisture during extended storage at cabinet temperatures. This fact coupled with a growing demand for single service containers necessi— tates additional research concerning the effectiveness of our 1C6 cream cartons under practical storage conditions. 2 It is the purpose of this study to determine, if possible, where the moisture is being lost from the ice cream carton, and to outline some factors believed to influence the loss of moisture in packaged products. It is hOped that these findings may aid the ice cream manufacturer in combating this problem. Since little information relative to moisture loss in ice cream has been reported in the literature, sources other than those concerning ice cream have been consulted for reference material. The literature of the frozen foods industry has pro— vided the richest source of information on the factors respon— sible for the loss of moisture in packaged frozen products. REVIEW OF LITERATURE Evidence of Moisture Loss in Packaged Foods Cheese Investigations of weight loss in cheese during ripening and storage first appeared in the literature during the years 1897 to 1905. Van Slyke (1901) noted that unparaffined- cheddar cheese lost 11.14 per cent of its total weight when placed in 600 F. storage for 15 months at a relative humidity of 75 to 80 per cent. It was also noted that cheeses containing the greatest percentage of moisture lost the most weight. Later investigations by Van Slyke _e_t_ 31; (1903) showed that larger cheeses lost less moisture per 100 pounds of cheese than did the smaller sizes of cheese. In all cases, higher storage temperatures resulted in a greater moisture loss. Babcock gt a_l. (1903) found that at a constant humidity, the amount of moisture lost from cheese would be greatest at higher storage temperatures, but this loss could be reduced by increasing the relative humidity of the storage room to 100 Per cent. 4 In a study of the effect of salt migration on the moisture content of cheddar cheese, Hoecker and Hammer (1944) found that the cheese lost about seven per cent of its moisture in four months of ripening. The moisture content decreased sharply at the surface and center of the product during the first 15 days of pressing; then tapered off. Paraffin coatings were used on experimental cheeses by Van Slyke gt §_1_. (1903) and Lane (1903) and it was found that after five months of storage, the non—paraffined cheese lost a greater percentage of moisture. These paraffin coat— ings had little effect on the flavor of the cheese. The effect of several coverings applied to cheddar cheese was studied by McCubbin and Reichart (1937). They observed that comparative moisture tests at five months of ripening revealed that para— film—covered cheese contained about two per cent more mois— ture than cheese covered with paraffined celIOphane. Also, celIOphane—covered cheese contained three to four per cent more moisture than paraffined cheese. In a review of the changes that have occurred in cheese curing and types of coverings for cheese, Reichart and Downs (1941) concluded that the greatest economy in retarding moisture evaporation of cheese was obtained by combining paraffin coat- ings with curing at low temperatures. Templeton and Sommer (1937) in investigating wrappers for processed cheese noted that the wrapper must maintain the moisture within the cheese. However, certain wrapping materials caused flavor deteriora— tion. This was evident particularly when the cheese was still hot at the time of contact with the wrapper, or when heat was needed to seal the wrapper. Butter The loss of weight in butter has been accorded a matter of serious consideration, since butter is sold on the basis of weight. Salted and unsalted drums of butter were stored by Washburn and Dahlberg (1917) at -15° F. for 284 days. The salted butter lost 2.70 per cent of its moisture whereas the unsalted butter lost 0.19 per cent. Guthrie (1917) stored 100 tubs of butter at 00 to —100 F. for 134 days and observed an average shrinkage of 0.29 per cent. Seventeen tubs showed an increase in weight from 0.5 to 27.5 ounces, while 83 tubs lost weight ranging from 0.5 to 15.5 ounces. Hunziker and Hosman (1920) stored an unsalted pound print of butter at 750 F. for a month and found that the mois— ture content of the interior of the print was six to thirteen times greater than that of the outside, which had lost moisture through evaporation. The moisture loss of "leaky" butter was investigated by Dahlberg (1922), who found that butter made "leaky" lost 4.2 per cent in weight during six months storage at 45° F. , while its control lost only one per cent under the same storage conditions. Another study of "leaky" butter by Guthrie (1926) showed that underworked butter lost 3.54 per cent moisture during eight months of storage at 0° to 50 F., while the same butter "worked" ten more revolutions lost only 0.64 per cent in weight under the same storage conditions. Guthrie pt 31. (1936) observed shrinkage in twelve butter samples held 36 days at 50° F. The losses ranged from 0.44 to 2.02 per cent, with the average loss being 1. 14 per cent. In a study of the effect of aluminum foil as a butter wrapper, Ziemba (1947) observed that the moisture losses of the control samples were 2.25 per cent greater than in the foil—wrapped butter . In. I' . _'.DHI. .I.F . Ice Cream It has been generally accepted in the ice cream industry that shrinkage of ice cream manifests itself as a loss of vol- ume, but relatively few investigators have studied weight losses in ice cream. Smith (1935) was one of the first investigators to study changes in the weight of ice cream during storage. The conclusions reached were of a negative nature in that pack— aged ice cream did not materially change in weight over stor— age periods of 16 to 24 weeks. Of 520 packages stored at —60 F. in an automatically—controlled hardening room, only 21 varied greater than five grams from the initial weight. No change in weight occurred in 33 per cent of the 520 packages; 51 per cent lost weight; and 16 per cent gained weight. No further research relative to ice cream and moisture losses could be found in the literature until Meiser (1950) re— ported weight changes in packaged ice cream at cabinet tem— peratures. An average loss in weight of 20 grams per pint was observed during 24 weeks of storage at 7° F. in untreated pape r containe r s . Meat Pleuthner (1939) stated that a quarter of beef stored at 320 F. will lose weight at the rate of 0.60 per cent per day at a relative humidity of 75 per cent; 0.30 per cent per day at 85 per cent; and 0. 12 per cent at 95 per cent. At 400 F. storage, a quarter of beef will lose weight at the rate of 0.76 per cent each day at a relative humidity of 75 per cent; 0.45 per cent at 85 per cent; and 0. 15 per cent at 95 per cent. Hiner and Hankins (1941) noted that moisture losses will occur in meat stored at temperatures above freezing, even when covered with a relatively vapor—proof wrapper. Beef aged 35 days at 340 F. in moisture—vapor—proof ce110phane lost 4.58 per cent of its moisture. Liver sausage wrapped in a polyethylene film, as ob— served by Lauber _e_t 3.1. (1949), lost only 0.2 per cent of its moisture during three weeks storage in a refrigerator. Nor- mal storage of liver sausage for 10 to 14 days at 400 F. , caused a loss in weight of 10 to 12 per cent. Various Frozen Foods The literature of the frozen foods industry contains many investigations concerning moisture loss in meats, veg— etables, and other frozen foods. Brookbank (1949) stated that the loss in weight of unwrapped frozen meat can amount to 10 per cent or more over storage periods of six months. The loss of weight in chapped steak wrapped in regenerated cellu— lose and stored 292 days at 00 F. was 5.1 grams per pound, or 1. 12 per cent, as reported by Grant (1944). DuBois and Tressler (1939) stored meats for six months at —50 to —100 F. A and a relative humidity of 40 per cent. Meats wrapped in waxed paper showed the following weight losses: beef lost 4.6 per cent; pork lost five per cent; veal lost six per cent; and lamb lost three per cent. The effect of fluctuating storage temperatures on ground beef during six months of storage was studied by Hustrulid _e_t _a_l_. (1949). Beef wrapped in a good quality locker paper lost an average of 5. 72 per cent moisture when the storage temperature fluctuated from 00 to -10° F. Beef wrapped in the same paper, but stored at a constant 00 F. lost an average of 1.82 per cent in weight. 10 In a study of surface drying of poultry, Cook (1939) found that severely dehydrated muscle contained only 50 to 55 per cent moisture, whereas normal tissue contained about 72 per cent moisture. Thus, severe dehydration caused a loss of about one—third of the moisture originally present in the muscle. DuBois (1942) observed that at 00 F. chickens lost not greater than 0.5 per cent moisture in a year in a moisture- vapor—proof package, while chickens in waxed locker paper lost five per cent or four ounces per five—pound bird. The moisture losses of deboned turkey steaks were investigated by Klose st 31. (1950). The white meat wrapped in waxed paper lost 8.8 per cent of its original weight after six months at 0° F.; whereas, the dark meat lost 11.9 per cent under the same conditions. Graul and Lowe (1947), in studying the effect of stor— age on frozen cakes and batters, found that the frozen cakes lost 2.08 per cent moisture at 00 F. and 0.63 per cent at -100 F. during storage of eight months. The moisture loss for frozen batters during the 8 months of storage was 1.00 per cent at 00 F. and 0.83 per cent at —100 F. It was stated that the cakes and batters were packaged in relatively moisture- ll vapor—proof packages, otherwise the moisture loss would have approached the limits of the total moisture content of these foods. An extensive study of the effects of packaging on mois— ture loss of frozen foods was made by Woodroof (1941). The following weight losses for frozen fruits and vegetables were observed after storage of one year in poor packages: String beans lost 22.1 per cent; peaches lost 12 per cent; young— berries lost 58 per cent; strawberries lost 60 per cent; and lima beans lost 11.1 per cent. Youngberries, when hermet— ically sealed in glass bottles and kept frozen for two years, lost 38 per cent of their moisture to the void within the con— tainer. This loss took the form of ice on the inner walls of the container. Stone (1930) observed that unwrapped marshmallows lost 10 per cent in weight during storage of two weeks. Marsh- mallows wrapped in waxed paper and glassine lost 7 per cent and 3 per cent moisture, respectively, during the same storage period. Woodroof (1941) found that the amount of desiccation depended not only on the type of package, but upon the kind 12 of product as well. Strawberries lost approximately six times as much in weight as did blueberries when the same conditions of freezing and storage were employed. Youngberries lost about half as much as peaches, but eight times as much as blueberries. Beef was found to lose about one—third as much as peaches with the same surface exposure, but less than any of the common vegetables tested. Moisture Loss Mechanisms The transpiration of moisture from packaged frozen foods- is a complex problem, because of the existence of two separate systems. One system is the package, with its dis- tinct pr0perties of pressures and atmosphere, while the stor— age room is another system entailing a different atmosphere and pressures of its own. Carson (1938) attributed the driving pressure in the moisture loss mechanism to a difference in vapor pressure, determined by the humidity and temperature on each face of the package. The transpiration of moisture, he felt, occurred in the presence or absence of air pressure, disregarding the fact that the circulating air had the capacity to contain the moisture or not. Thus, as the air became l3 saturated, the moisture condensed on the package in the form of frost. Initial Loss During Hardening Greene (1944) has -noted that serious dehydration is .possible in low temperature rooms during the period when the food temperature is being brought into equilibrium with the room temperature. In order to freeze food, there must be temperature differences between the food to be frozen and the air which does the freezing. There is also a temperature dif- ference between that of the refrigerating coils and the air. Pressure differences are produced by these temperature dif- ferences, and the moisture of the food under pressure will leave the food and pass into the surrounding atmosphere. There— fore, dehydration occurs as soon as the product is stored in the low temperature room, because of these temperature dif— ferences. Total Volume 5 Moisture migration may occur as a movement of total volumes through the porous walls of a package. In this type 14 of migration, the water vapor flows in the same manner as steam flows through a pipe. McDermott (1941) stated that an external force is required for this movement, and work is done in overcoming the external and internal frictional resistances involved. Diffusion Another type of migration, diffusion, may be involved in dehydration of frozen foods. McDermott (1941) has observed that an example of diffusion is the ability of perfume, when re— leased in still air, to permeate the entire volume of a room. Diffusion requires no energy dissipation, for the energy lost by one molecule to another remains in the system, and the transfer of molecules requires only that the density of the vapor be greater in some region than in some other. In such a case, a greater number of molecules are traveling from the dense to the less dense region. Since diffusion through solids occurs almost imperceptibly at low temperatures, it must be conceded that diffusion through ice cream packages, if occur— ring at all, will travel the route of Openings in the container wall. 15 Sorption With Subsequent Evaporation Sorption, the phenomena of binding of moisture in sol— ids, is another mechanism by which moisture may be trans— ferred. McDermott (1941) has noted that sorption is associated with pr0perties of solids, whereas movement of masses and movement by diffusion occur in the absence of solids or through the pores of solids. In addition to water as a part of the chemical or physi- cal composition, a solid may contain: adsorbed water, adhered to surfaces; absorbed water, within the pores; and water within capillaries, which is a combination of both. An adsorbed film is neither chemically bound nor "free" fluid. The film occu- pies a position midway between the two, just as it is neither a liquid nor a gas, since the film has a thickness of only one molecule. Capillary water can be compared to the wetting of a wick, where the film is extended along the wick through ad— hesive forces. These forces advance the boundaries of the film while internal forces of adhesion and cohesion renew the molecules leading the advance. Absorbed water is held loosely 16 within the pores of a solid. An example of this is the water that can be expelled from a sponge by squeezing. It appears feasible that an important mechanism of mois— ture loss through ice cream containers is the hygrosc0pic ac— tion of the package. The package becomes saturated with sorbed moisture and then releases this moisture to the sur— rounding atmosphe re . Factors Affecting Evaporation in Packaged Products Length of Storage Carson (1938) has observed that the amount of moisture passing through a membrane is directly preportional to the time of exposure. However, time is required (from a few minutes to several days, depending on the package material) for the sorption and evaporation of moisture to reach a steady state, so that the rate of transpiration becomes constant. Ex- tending the length of storage from three months to six months was found by Klose gt a_1_. (1950) to increase moisture losses in frozen turkey steaks an average of 225 per cent. A minimum period of exposure of 48 hours in the hard— ening room was recommended for ice cream by Ramsey gt §_1_. 17 (1947) in order to achieve maximum hardening. If this mini- mum storage period was not observed, moisture losses of the ice cream in retailers' cabinets was increased because of weakened resistance of the softer ice cream to the passage of moisture . Tempe rature of Storage The effect of storage temperature on moisture loss was studied by: Cook (1939), Dahle e_t 11.: (1947), Graul and Lowe (1947), Iverson (1947), Kohler (1939), McCubbin and Reichart (1937), Oswin (1948), Ramsey e_t _a_1. (1947), and Van Slyke _e_t_ 31. (1903). These investigators observed that the rate of evap— oration will generally decrease as the temperature is lowered. Both the vapor pressure of water and the moisture—holding capacity of the air will decrease as the temperature is lowered. Rabak (1947) observed that peas, frozen in paperboard with heat—sealed liners, lost twice as much moisture at 150 F. than at 00 F. during 20 months of storage with reasonably constant humidity. A widely fluctuating temperature, according to Woodroof (1941), was the biggest single cause of desiccation of frozen 18 products. In another study, Woodroof (1941) contended that moisture passed from the food into the air within the container when the temperature rose unless the container was completely filled and evacuated of air. When the temperature dr0pped, the moisture was deposited on the inner surface of the con— tainer as frost. Thus, more moisture left the product with each change in temperature. The mechanics of this release and refreezing of moisture outside the product is believed to be irreversible. Carson (1938) stated that the effect of a rise in temperature was to primarily increase the driving pressure, thus increasing the permeability to moisture. However, it is cautioned that some workers have reported greater increases than would be expected. When the system is not isothermal, McDermott (1941) noted, the transfer of moisture by diffusion and sorption may operate either in the same or in Opposite directions. Hustrulid e_t _a_1. (1949) observed that moisture losses in ground beef during storage of six months were more than three times greater for a fluctuating storage temperature of o 0 to —100 F. than they were for a constant 00 F. In addition to increased dehydration, Finnegan (1939) found that fluctuating 19 temperatures produced oxidation, structural damage, and re— adjustment of water in the product due to thawing and re- crystallization. It was found that relatively small fluctuations above 00 F. will cause much more damage than large ones at .20° F. Circulation of Air Differences in temperature were observed by Woodroof (1941) to cause air currents, with the warmest air rising to be re—cooled by the coils, and thereby, giving up moisture to the coils. This air again contacting the product will be less than saturated, and will tend to absorb moisture. On rising to the coils, the cycle is completed. Thus, the slowly—moving air will. constantly drain moisture from the product and deposit it on the refrigerating coils. Woodroof and Rabak (1949) noted that the movement of low—humidity air across the package sur— face will accelerate oxidation and the loss of flavor in addi— tion to increasing moisture loss. It was found by Cook (1939) that air appeared to exert a solvent action, particularly at low temperatures, thus re- taining a quantity of water vapor more closely related to the 20 vapor pressure of supercooled water than to that of ice. Greene (1944) theorized that if the circulating air had no further capa— city for containing moisture, vapor pressure differences, if present, caused the moisture to leave the food and condense on the product. Ramsey (1946) has noted that undue circulation of air in the hardening room increased the shrinkage of ice cream in paper containers. State of Moisture The work of Leighton (1927) and others indicated that ice cream is never completely frozen. In such a case, it seems possible that an ice cream package at —100 F. (a com— mon storage temperature) may contain moisture in the form of liquid, solid, and vapor. It has been noted by McDermott (1941) that adsorbed moisture is neither to be considered as a liquid nor a gas, because of the monomolecular nature of the film. Carson (1938) observed that certain materials, such as paper, will absorb and transmit moisture more rapidly if one face of the package is in contact with water, than if the paper is in contact with the saturated vapor from water. For ma— terials such as rubber, behavior in contact with moisture will 21 not differ, irregardless if it is in contact with the liquid or the vapor state . Humidity The free air within the frozen food container was ob— served by Rabak (1947) to approach 100 per cent relative ‘ humidity, while the atmosphere of the low temperature room 5 was usually far below saturation. Thus, a vapor pressure 1 difference was produced which caused the migration of water vapor. Cook (1939) found that frozen poultry stored at humid- ities less than 95 per cent was unsatisfactory, as the product was seriously affected by desiccation in from two to three months. Hutnidities from 98 to 100 per cent maintained the product satisfactorily for 83 weeks. Greene (1944) investigated the vapor pressure differ- ences between frozen foods and the freezer room air under different conditions of relative hmnidity and temperature. This study indicated that changes in the relative humidity of the storage space exerted greater influence on moisture losses than did comparative changes in the temperature of storage. The work of Pleuthner (1939) with storage of beef at 320 to 22 400 F. also indicated the importance of relative humidity. It was found that within the range of 31C) to 42° F. the effect of temperature changes was slight (about 25 per cent) when com- pared with that caused by a change in relative humidity from 75 to 95 per cent. One theory of moisture transmission advanced by Carson (1938) was that each side of the package membrane absorbed moisture according to the relative humidity on each side, and an equilibrium of transpiration was then obtained. Thus, a very high relative humidity on one face will upset the relation— ship between the vapor pressure and the rate of transpiration of moisture. McDermott (1941) noted that the total sorbed moisture within the package material was not generally a linear function of the relative humidity, but increased rapidly after a relative humidity of 80 per cent had been reached. This increase was believed to be due to the accumulation of inter— stitial or absorbed water, which was much less at lower rel— ative hurnidities. Babcock e_t _a_l. (1903) found greater moisture losses in cheese stored in boxes at higher temperatures than in cheese stored in boxes at lower temperatures. The relative humidity 23 of the boxes was measured, and it was found that in boxes of cheese stored at 35° to 400 F. , the air was saturated. At the higher temperatures, the relative humidity of the boxes was low enough to allow the evaporation of moisture from the cheese. Cheese stored for 15 months at 75 to 80 per cent relative humidity was found by Van Slyke (1901) to lose 11 per cent moisture, while cheese stored in a saturated atmosphere in a bell jar for 15 months gained two per cent in weight. Surface Coating on the Product Since the efficiency of any package is to a great ex— tent dependent upon the tightness of the seal, it is natural to conclude that an ideal food covering would consist of an unin— terrupted film of protective material applied as a dip coating directly to the product. A film having the required chemical and physical characteristics correctly applied, supplies a protection that approaches the efficiency of a hermetically— sealed metal or glass container. Dip coating of cheese with paraffin has long been practiced with quite satisfactory results, but this practice has not entirely eliminated moisture losses. Another type of surface coating is the glazing of fish by dipping 24 the frozen fish into a cold water solution for an instant. This leaves a thin coating of ice on the fish which almost eliminates desiccation. Rabak (1947) has described capably the natural protec- tive coatings of fruits, seeds, and nuts. The covering of such fruits as apples and pears consists of a thin coating of mois— ture—resistant waxes. This coating retards vapor losses, but permits respiration. The peanut is an example of Nature's "double wrap," while the cocoanut is Nature's hermetically- sealed container. Woodroof (1941) and Greene (1944) have observed that the amount of desiccation of frozen foods is influenced by the exterior skin or shell of some products. Very quick freezing of foods, especially when in contact with dry ice, will produce an icy crust on the surface of the food. This crust will retard moisture losses by acting as an insula— tion for the interior of the product. Woodroof (1941) noted that the duration of this protection was short, with the most protection being given during the first five days of storage and steadily diminishing for 40 to 60 days. 25 Vapor Pres sure Differences The driving force behind the transpiration of moisture in packaged frozen foods has been generally attributed by au— thorities to the differences in vapor pressure that exist between the interior and exterior of the package. In outlining formulae for the calculation of permeability of packaging materials, Oswin (1948) stated that the rate of moisture—vapor transmis- sion was preportional to the vapor pressure difference across the material. Carson (1938) admitted this to be true generally, but cautioned that important exceptions have been observed, and that the vapor pressure within the container cannot always be determined. The difference in vapor pressure is determined by the temperature and the humidity on each face of the mem— brane. Greene (1944) listed the vapor pressure differences for some of the common storage temperatures and humidities. It was noted that a large temporary difference existed during freezing of the food, while that experienced during storage of the frozen food was much smaller. In comparing the ef— fects of these vapor—pressure differences, it must be remembered ‘1" A mnna._1mu—_ -u . 26 that exposure time is relatively short during the time when the food temperature is being brought down to room temperature. Packaging The importance of the package in retarding moisture loss of frozen foods should not be overlooked. It appears that a few of the least permeable packaging materials afford such a degree of protection that the adverse effects of fluc— tuating storage temperatures and low humidity are almost neg— ligible. Penn (1945) has advocated that in evaluating a pack- age, 75 per cent of the score should be based on the protective qualities of the package. The other 25 per cent should be based on the sales appeal of the package. Surface Area A cylindrical container with tapered sides, termed nestyle, is widely—used in the ice cream industry. Meiser (1950) ob— served that tall nestyle packages were more resistant to mois— ture transfer than were squat nestyles. Since both containers were constructed of the same weight paper, it appeared that 27 the greater surface area of the squat nestyle may explain its inferiority. Thickness of Packaging Material Carson (1938) observed that there is some uncertainty as to how permeability to moisture varies with the thickness I of the package material. For a consumer standard, the thick— 5., ‘. ness should be of less concern than the over-all permeability. i McDermott (1941) noted that one investigator found resistance to low velocity air to be more influenced by density than thick— ness, while others have observed resistance to water vapor transfer to be non—linear with thickness. It was found by Meiser (1950) that thickness may account for the greater re— sistance of cylindrical containers to water—vapor transfer, when compared to nestyle containers. The unfilled nestyles aver— aged 25 grams in weight, while unfilled cylindrical containers averaged 33 grams. The effect of dOuble wrappers on moisture loss of frozen foods was investigated by Rabak and Stark (1946). It was found that double wrappers increased the resistance of waxed paper to vapor transfer fivefold, while that of ceIIOphane 28 was increased threefold. Possibly, the second overwrap re— sults in partial resealing of the porous areas of the first overwrap by transferring coating from one sheet to the other during heat-sealing. Heat Transfer No mention of the effect of heat transfer of packaging ' \‘n ‘4'; -\- . materials on water—vapor transmission could be found in the literature. However, Stone (1930) claimed that waxed glassine exhibited superior heat—insulating prOperties. Two cartons of ice cream were allowed to stand for 45 minutes at 800 F. The control carton, upon inspection, contained ”mushy" ice cream; while a carton wrapped in glassine and heat sealed, "contained a firm, solid brick with only traces of melting at the corners. " A carton with superior resistance to heat transfer may be also more resistant to water—vapor transfer, if for no other reason than its protection against fluctuations in storage temperature. Closure Seal The ice cream industry has almost ignored the irnpor— tance of a "water-vapor proof" closure seal; while the frozen Z9 foods industry, in its few years of develoPment, was quick to recognize the effect of a poor seal. Rabak (1947) has noted that an imperfect seal will defeat the utility of the most effi— cient water—vapor resistant material. The poor seal was believed by Woodroof and Rabak (1949) to be the point of great— est loss of water vapor. These investigators recommended that the seal should be as good as the package, while Shaffer \ _" 12 "annex-Jun. ’3‘ ,1. a . “film" I (1945) observed that no package is better than its seal. Poor seals permit leakage before and after freezing. Packaging Material The following list by Woodroof and Rabak (1949) con— tains some of the types of packaging materials that have been found satisfactory for frozen foods: waxed papers moisture and water—resistant ce110phanes laminated materials rubber and rubber derivatives aluminum foil coated paperboard dip coating tin, aluminum, and glass This list is being constantly supplemented with new materials. Many of these materials may be useful to the ice Cream industry. 30 The literature is rich in data of the water—vapor trans- mission rates of materials used for packaging of frozen foods; Brookbank (1949), Carson (1938), Dahle e_t §_l_. (1947), DuBois (1942), DuBois and Tressler (1939), Grant (1944), Levy (1931), and Woodroof and DuPree (1942). Evaluation of the results has been difficult because of the variety of conditions under which the tests have been conducted. Carson (1938) has stand— ‘ WT. : r.- aJ-‘r-J- "-1-. saw Av . . ’ ‘ “a .n ardized the results of 28 investigators into common units of measurement. Among the variations noted in the 28 tests were: The test period varied from two to 2,000 hours. The temperature of the test varied from 7° to‘ 113° F. The area tested varied from 0.02 to 50 square inches. Vapor pressure differences varfled from zero to 72 mm. Hg. e. The results were reported in 20 different units. 9.00“” The majority of tests have been conducted at tempera— tures above freezing. Brookbank (1949) believed this to be unsound since results reported at 1000 F. may be entirely different at 00 F. The paper industry is aware of this dis- parity, and research is being conducted to prepare a standard— ized test for determining the permeability of packaging ma— terials at sub-zero temperatures. 31 Physical and Chemical Effects of Moisture Loss Flavor Deterioration Vanilla ice cream of high quality was found by Schricker (1935) to show the effects of age within four weeks from date of manufacture under normal conditions of storage. Chocolate ice cream deve10ped "off—flavors" within four to six weeks, and strawberry within two weeks. Arbuckle (1949) observed that ordinary ice cream packages must be supplemented with additional wrappers of protective materials if subjected to zero temperatures of storage for six weeks or longer. It was recommended that dairy products at low temperatures should be stored separately to eliminate absorption of flavors. Smith (1935) stored ice cream samples at a constant —60 F. , and noted flavor changes in vanilla ice cream at 86 to 100 days of storage. Strawberry ice cream turned slightly stale at 72 to 107 days, with a disagreeable stale flavor noted at 114 days. Chocolate and maple walnut ice creams kept well and retained their flavors for three to four months. A number of frozen food investigators have studied "freezer burn, " a local dehydration of frozen food tissue. ‘JI’I'I‘d V . . 32 Brookbank (1949) observed that air pockets between the food and the wrapper are focal points for this dehydration. The wrapper was colder than the meat, causing vapor to condense on the wrapper around the air pocket. Cook (1939) and Rabak (1947) have attested to the flavor changes caused by "freezer burn. " Surface Films Smith (1935) noted that of 520 ice cream samples stored at a constant -60 F. , all showed a tough, rubbery film on the surface after 107 to 114 days of storage. Meiser (1950) found a tough, leathery film of approximately 1 millimeter in depth in ice cream samples stored at 70 F. for eight weeks. In this case, it seemed reasonable to attribute this surface film to the dehydration of the surfaée. Shrinkage Kohler (1939) observed that two types of ice cream shrinkage exist. When refrigeration is applied severely to ice cream, a meniscus—like type of shrinkage will occur, causing the center of the ice cream to be depressed. Another 33 type of shrinkage results in the ice cream receding from the wall of the container and sinking to a lower level. This lat- ter type shrinkage may be produced by severe pressure changes, or, as shown by Meiser (1950), may result from severe desic— cation of the product. Dehydration of this magnitude resulted in a loss in weight as well as a loss in total volume of the packaged ice cream. Whether two types of shrinkage actually exist is still a debatable question that can only be answered by furthe r expe rimentation . PLAN OF EXPERIMENT From the foregoing discussion, it is evident that frozen foods will lose weight during storage. This loss of weight is believed to be due to evaporation of moisture from the product. ' Those known factors influencing the rate and degree of desic— cation have been discussed previously in the review of liter— ’x‘ux . ‘( ature. There is some evidence that packaged ice cream will also lose weight through evaporation during storage, as shown by Meiser (1950). Since investigators in the frozen foods industry have found certain factors to influence moisture loss, it is the pur— pose of this study to determine, if possible, the effect of some of these factors on moisture losses in packaged ice cream. In other words, what part of the product is losing moisture, and how does this loss affect that part? Because ice cream is subjected to many varied proce— dures of packaging and storage, it is evident that the sc0pe of this study must be limited to the facilities available on a lab— oratory scale. With this viewpoint in mind, the following ex— pe riments were performed: 35 1. Plastic Containers. Ability of rigid plastic con— tainers to retard weight losses in packaged ice cream. 2. Container Lids. Ability of container lids to retard weight losses in ice cream packaged in untreated cylindrical paper containers. 3. Position of Paraffin. Ability of the lateral and horizontal surfaces to retard weight losses in paper cartons. 4. Saturation. Ability or inability of saturated paper to retard weight losses in untreated paper containers. 5. Storage Temperature. Ability of sub-zero tempera— tures to retard weight losses in varied ice cream cartons. 6. Peel Test. Ability of varied ice cream cartons to resist adhesion of the ice cream to the container surface. 7. Shrinkage. Ability of plastic—coated containers to resist shrinkage as measured by volume loss and weight loss. 8. Surface Retention of Moisture. Ability of lateral and horizontal surfaces of varied ice cream containers to resist desiccation and flavor deterioration. GENERAL PROCEDURES The following procedures were followed generally through- out the experiments. In cases where the procedures listed be— low were modified, the modifications will be described under It 1 their prOper headings throughout the remainder of the study. Composition of the Mix Mixes testing approximately 12 per cent butterfat, 11 per cent milk solids not fat, 15 per cent sugar, and 0.5 per cent gelatin of 150 Bloom strength were obtained from the Michigan State College Creamery. Mix Ingredients Frozen cream and whole milk supplied the butterfat for the mixes used in the experiments. Additional milk—solids- not—fat were supplied by fresh skim—milk and roller-process skim—milk powder. Sucrose and sweetose were the sweetening agents used, while the stabilizer consisted of gelatin with an added whipping aid. The mixes were pasteurized at 1550 F. for 30 minutes; then homogenized in two stages with 2,000 pounds 37 pressure on the first stage and 500 pounds pressure on the second stage. Following homOgenization, the mixes were cooled on a surface cooler and stored in a holding vat at 330 F. for 24 hours prior to freezing. Freezing and Packaging The mixes were frozen in a VOgt continuous freezer (200 gallons per hour capacity), or in a 40 quart Cherry— Burrell direct expansion batch freezer. The samples were taken directly from the Vogt freezer, when the desired over— run (90 per cent) was reached, and placed immediately in the hardening room. The batch—frozen ice cream was packed by hand into pint containers and immediately placed in the hard— ening room. The first and last portions drawn from the batch freezer were not used in the experiments, and the hand—pack— aging was done as quickly as possible in a cold storage room to eliminate errors caused by softening of the ice cream. All samples were hardened at ~90 F. :0: 10, then transferred to a o 0 closed electric cabinet at a temperature of 7 F. :I: l . 38 ProducinLShrinkage In all cases except one, shrinkage was produced in a natural manner by allowing extended storage of the ice cream at cabinet temperatures. In one experiment, shrinkage was obtained using a modification of Hankinson's (1942) vacuum induction method. The frozen ice cream was exposed to a vacuum of 20 inches for four hours. The vacuum was then released and the samples were returned to the storage cab- inet for seven days before being investigated for shrinkage. It has not been conclusively shown that shrinkage produced by vacuum treatment is identical to that which occurs in spontaneous shrinkage . Measurement of Moisture Loss In all except the last two experiments, moisture loss was determined by weighing techniques. The containers were weighed on a triple—beam, stainless steel balance having a sensitivity of 0.1 gram. Weighings were made of the unfilled containers and of the filled containers after hardening. At intervals of one week the containers were removed from the ‘I‘P‘-X‘_.."-€"I ,w" . 39 cabinet and re—weighed rapidly. The lids of the samples re— mained in place during the entire storage period. In the last two experiments moisture loss was deter— mined by analysis of the ice. cream for total solids; since, theoretically, the loss of moisture should be prOportional to the increase in total solids of the ice cream during storage. The Mojonnier method as outlined in Mojonnier and Troy (1925) was used for the total solids analysis of the ice cream samples. -«~. arty—T ‘.' \WE‘PM s... ‘W EXPERIMENTAL Pla stic Container 5 Brookbank (1949), Carson (1938), DuBois and Tressler (1939), Stone (1930), Woodroof and DuPree (1942), and Wood— roof and Rabak (1949) have presented evidence in the literature to show the efficiency of plastic materials in retarding moisture loss when used as package coatings or as wrappers. However, no attempt was made to utilize containers manufactured of solid plastic which are now being used quite widely by the cheese industry. To determine the ability of rigid plastic containers to retard moisture loss in packaged ice cream, the following experiment was conducted. The containers were filled directly from the continuous freezer and stored for eight weeks in the ice cream cabinet. At weekly intervals, the samples were weighed and returned to the cabinet. The results are illustrated in Figure 1; each point plotted was the average of triplicate determinations. The containers used are listed below: I O I m I 0‘ I '0 O C.) LOSS IN WEIGHT (.GRAMS PER DINT) a + o' , 2 4 6 9 LENGTH OF STORAGE (WEEKS) Figure 1. Effect of rigid plastic containers on weight losses of ice cream at cabinet temperature. A - Untreated cylindrical. B - Cylindrical plas- tic. C - Rectangular plastic. 41 42 Container A — Untreated control (cylindrical paper carton). Container B — Cylindrical container of heavy weight plas— tic (screw—type lid). Container C - Square container of heavy weight plastic (insert-type lid). Both plastic containers were vastly superior to the un— treated paper carton. The square plastic container lost slightly less moisture than the round plastic container, possibly be— cause the insert lid provided a tighter closure than the screw- » (F.,..umsf‘rwz aim! type lid. The weight loss of the plastic containers was so slight, however, that the small difference between the two must be considered insignificant. Because plastic is not hygrosc0pic or porous, it is reasonable to assume that the moisture loss did not occur through the known processes dis— cussed previously, but occurred at the junction of the lid with the container prOper. At the present time, plastic containers of this style are not practical for packaging of ice cream because of their cost; however, we cannot disregard future use of this type of pack— age. Lighter—weight plastics in the form of package coatings and bags may be satisfactory for ice cream merchandizing. 43 Effect of Lids In the early stages of the ice cream industry, it was a common practice not to use lids on metal containers of ice cream. In most cases, a single sheet of thin parchment was the only covering afforded the surface of the product. The importance of closures has been mentioned previously in this study. Rabak (1947), Shaffer (1945), Woodroof and Rabak (1949) are in general agreement that a package is no better than its closure seal, thus the following experiment was planned to determine the degree of protection offered by the lids of ice cream containers. Six cylindrical containers (untreated) were filled with ice cream and stored for eight weeks at cabinet temperatures. The lids were removed from three of the cartons after hard— ening, while on the other three cartons the lids remained in place during the entire period of storage. At weekly intervals the six cartons were weighed, and the results recorded in Figure 2. Curve A represents the average of containers with the lids removed, while Curve B represents the average of the containers whose lids remained in place during the study. 44 LOSS IN WEIGHT IGRAMS PER PINT) 2 4 o 8 LENGTH OF STORAGE (WEEKS) Figure 2. Effect of container lids on weight losses of ice cream at cabinet temperature. A — Lids removed. B - Lids in place. 45 The results show that after eight weeks of storage, the containers with lids removed lost an average of 12.4 grams, while the average loss of the containers with lids in place was 8.8 grams. This indicates that the closures of the c0n— tainers offered some protection. Although the amount of pro— tection may appear small when the weight losses are compared, it must be remembered that a minute decrease in moisture content may produce pronounced changes on the macrosc0pic surface layers. The frozen foods industry who thoroughly investigated this problem of closures concluded that heat— sealing is an indispensable operation in frozen food packaging. Ice cream does not react favorably to heat—sealing, but per- haps other means may be found to eliminate this avenue of escape. Further studies relative to the importance of proper closures appear on subsequent pages. Position of Paraffin The previous experiments indicated that ice cream will lose weight when stored in untreated paper containers. Dahle e_t 31. (1947) and Meiser (1950) have investigated the effect of paraffin coatings of containers on shrinkage of ice cream. These 46 investigators paraffined the containers on the interior and ex— terior to determine at which position paraffin offered the great- est resistance to shrinkage. The procedures of Dahle gt 31. (1947) and Meiser (1950) were modified in the following experiment in that partial areas of the container were paraffined to determine where the weight was being lost. Cylindrical paper cartons were coated with paraffin at different positions on the outside of the containers by dipping the cartons in melted wax. The cartons were then filled with ice cream and stored for eight weeks at cabinet temperatures. Following weighings at weekly intervals, the re— sults were plotted in Figure 3. Triplicate samples were made of each treatment listed below: Carton Treatment A Untreated control B Paraffined on bottom C Paraffined on tOp D Paraffined on t0p and bottom E Paraffined on side F Paraffined on t0p, bottom, and side -8 .. A I'- z 6". «*6 C u.) a. m D 32.4 S "’ E E c.9_ F a 2 E E 0 {’8 o _J+l O 2 4 b 9 LENGTH OF STORAGE (WEEKS) Figure 3. Effect of position of paraffining on weight losses of ice cream at cab— inet temperature. A - Unparaffined. B — Paraffined bottom. C - Paraf— fined tOp. D — Paraffined top and bottom. E — Paraffined side. F — Completely paraffined. 47 48 Visual inspection of Figure 3 indicates that the most moisture was lost through the side of the container. However, when the weight losses of the t0p, side, and bottom of a pack— age were divided by their respective surface areas, one found the loss in grams per square inch to be greater for the hori- zontal surface. In calculating the loss per unit area, it must be assumed that B subtracted from A would give the loss through the bot— tom. Similarly, C and E subtracted from A would give the losses through the tOp and side, respectively. Then, if these losses were divided by the areas of the parts, the loss in grams per unit area could be found for each component. Us— ing this method, the following losses were found: Area Studied Loss in Grams per Square Inch T0p 0. 149 Side 0. 129 Bottom 0.065 The greater loss at the tOp of the container was pos— sibly due to a greater volume and circulation of air at this 49 point. Since packages were stored adjacent to each other, as is common in the dealer's cabinet, the sides were protected from air currents by the proximity of neighboring packages, while the tOps were unobstructed. Another explanation may be that the temperature in the cabinet was higher at the tOp of the container, causing more moisture to be lost. This same reasoning may account in part for the smaller losses at the bottom, where the temper— ature should be lower since the warmer air will rise. Also, the bottom was protected quite efficiently from the circulating air by a lip which extended downward from the side of the carton for a short distance. This lip, which is intended pri— marily to strengthen the carton, formed a small chamber that trapped air around the bottom and acted as an insulating agent. Saturation Carson (1938) and McDermott (1941) observed that hygro— sc0pic prOperties of packaging materials facilitate the passage of moisture. Paper containers were believed by Meiser (1950) to absorb moisture from the ice cream. He maintained that '. Rz-u_'i¥r-"n. .gm,.—' «0 .-; :1 50 paper once saturated accelerated a bleeding of moisture from the product to the less dense atmosphere. With the above thoughts in mind, an experiment was devised to determine the effect of saturation of the package prior to filling. Cylindrical containers of different treatment were saturated by allowing them to absorb moisture in the ice cream cabinet for seven days prior to filling with ice cream. Unsaturated containers of similar treatment were also filled with ice cream and stored with the filled saturated con-— tainers in an ice cream cabinet. All packages were weighed at intervals of one week. The results are shown in Figure 4. The containers used in the experiment are listed below. Each determination was made in triplicate. Sample Treatlnent A Saturated cylindrical (untreated) B Unsaturated cylindrical (untreated) C Saturated cylindrical (glassine-lined) D Saturated cylindrical (paraffined) E Unsaturated cylindrical (paraffined) F Unsaturated cylindrical (glassine—lined) ‘1. ':‘ I'. I 5 51 I (D I 0 I -h I M LOSS IN WEIGHT (GRAMS PER PINT) O +I~ 834 l” [I l’ [I I’ C / / / I [I z’ D I _._; = o 2 4 6 8 LENGTH OF STORAGE (WEEKS) Figure 4. Effect of saturation of carton on weight losses of ice cream at cabinet temperature. A - Saturated (un— treated). B - Unsaturated (untreated). C - Saturated (glassine—lined). D — Saturated (paraffined). E — Unsatu— rated (paraffined). F — Unsaturated (glassine—lined). 52 In all cases, saturation of the paperboard prior to packaging facilitated moisture transfer from the container to the cabinet air. Saturation had the least effect in the case of paraffined containers, since the paraffin coating reduced the number of pores by filling the interstices between the fibers. The small amount of saturation shown in the paraffined contain— ers probably occurred through capillary action in the longer unhydrated fibers, as paraffin does not always seal the ends of these fibers. It is not known why the saturated glassine—lined con— tainer differed so widely from its unsaturated counterpart in the amount of moisture lost. This may have been due to a loosening of the glassine layer from the container prOper, a factor previously reported by Hicks (1950) as influencing moisture loss. Meiser (1950) observed that a fairly uniform rate of moisture loss will be reached after the paper becomes satu— rated. In the studies conducted here, an almost steady loss of moisture was shown for the saturated containers, whereas the unsaturated containers lagged for about ten days before 53 a steady rate was reached. Possibly, this lag period parallels the time required for saturation. Temperature Moisture losses in frozen foods will generally decrease as the temperature of storage is lowered, as observed by a number of investigators, Cook (1939), Dahle e_t §_l. (1947), Graul and Lowe (1947), Iverson (1947), Kohler (1939), McCubbin and Reichart (1937), Oswin (1948), and Van Slyke gt _a__1_. (1903). Low storage temperatures for ice cream have been recom— mended by Ramsey gt a1. (1946), (1947), but no evidence could be found in the literature as to the effect of low temperature storage on moisture loss in ice cream. An experiment was designed to provide information on weight loss of ice cream when stored in various packages at two temperatures. The ice cream was filled directly from the continuous freezer into various containers, with triplicate samples of each package being stored at 70 F. in an ice cream cabinet and at —100 F. in a sub—zero unit. Weighings were made prior to storage and after four weeks of storage. The packages used and their changes in weight are listed in Table I. TABLE I WEIGHT CHANGES IN VARIOUS ICE CREAM PACKAGES STORED AT TWO TEMPERATURES 54 Average Change in Weight (grams) Container .10° F. 7° F. Untreated cylindrical — 3.70 6.42 Glassine cylindrical - 0. 25 0. 05 Untreated tub - 6. 30 4. 42 Paraffined tub + 0. 22 O. 52 Untreated pail - 9. 47 4. 85 Paraffined pail -— 1. 72 0. 87 Paraffined square — 3. 75 O. 25 Untreated nestyle — 7. 32 3. 75 Vinylite nestyle — 1. 20 0. 85 Paraffined nestyle - 0. 05 0. 60 Pliofilrn bag - O. 35 0.15 Ce110phane bag -12. 36 9.25 55 Of all the packages included in this study, only one sample (untreated cylindrical container) lost more moisture at the higher storage temperature. This is contrary to results reported previously for such frozen foods as meats, vegetables, and fruits. Communication with certain ice cream manufac— turers who are using these low temperature units has indicated experiences similar to that recorded here. Although no con— clusions can be drawn from this experiment due to its con— flicting nature, it does point out the need for an isobaric study relative to ice cream storage at different temperatures. An experiment of this nature, however, is too costly and time— consurning to be included in this thesis. Peel Test One criticism of untreated containers obtained from ice cream manufacturers is that ice cream, upon continued stor— age, has a tendency to cling to the surface of the package, thus making dispensing an arduous procedure. No reference to this criticism could be found in the literature, thus the fol- lowing expe'riment was designed to obtain this information. 56 Containers of ice cream similar to those used in the previous experiment were examined following storage of four weeks in an ice cream cabinet and sub—zero unit. The pro— tective package surrounding the ice cream was carefully stripped off while the ice cream remained firm. The amount of ice cream adhering to the package was observed and the results recorded in Table II. It was found that containers allowing the greatest degree of moisture loss also retained the greatest deposit of ice cream on the peeled container. Deposits of this nature are very ob— jectionable to the consumer. The adhesive deposit retained on the wall of the untreated containers was severely dehydrated and possessed a pronounced stale flavor. The ice cream clinging to the surface of the treated packages had a flavor not unlike the ice cream contained in the rest of the package. Shrinkage Shrinkage of ice cream manifests itself as a loss of volume, in which the ice cream pulls away from the walls of the container and, in some cases, sinks to a lower level. Dahle e_t 31. (1947) has presented evidence showing treated 57 TABLE II AMOUNTS OF ICE CREAM ADHERING TO VARIOUS CONTAINERS Container Amount of Deposit Untreated cylindrical +++ Glassine cylindrical + Untreated tub +++ Paraffined tub ++ it Untreated pail +++ Paraffined pail + Paraffined square + Untreated nestyle +++ Vinylite nestyle + . Paraffined nestyle + Pliofilm bag + Ce110phane bag ++++ 58 paper containers to be resistant to shrinkage. Previous ex- periments have shown treated containers to be resistant to moisture loss of packaged ice cream. Therefore, a comparison of the air transmission and water transmission rates of various packages under identical storage conditions should be a criteria ‘1vu'hi..._y upon which packaging materials are selected. E. To test this theory, nine nestyle containers obtained from a commercial manufacturer and coated with varying weights of plastic material were filled with ice cream and stored for four weeks at 70 F. in an ice cream cabinet. At the end of this storage period, the containers were weighed to determine the moisture loss. Similar containers filled with ice cream were subjected to vacuum treatment for four hours; then stored in the same ice cream cabinet for seven days. At the end of this storage period, the vacuum-induced shrinkage was measured by filling the void between the ice cream and the container with cold water from a burette. The values appearing in Figure 5 are the averages of triplicate samples of each container. The moisture loss is expressed as milligrams of moisture lost from each 100 grams 9 5 O 7 OCZuumnwa w2