2. One sheet of a thin moisture-vapor-re5istan.t heat-sealing cellophane Isminctted to Glassine or to sulfite paper by means of a permwnently plastic laminating agent. 3. Two sheets of the thin heat-sealing ~ldbphanelaminated together in same manner descrabed under film 2. (Presumably B mtlterial auch 8s MBAT cellophane would have these proper-
ties.)
The bag may be of Bat or gusset style or may be mechanically formed. It is sealed by application of hea,t or moisturevapor-resistant adhesive. Mter filling, the bags are closed either by heat sealing or by taping down in the prescribed manner, Section G-2 describes the outRide bag or envelope. This envelope consists essentially of a dense kraft paper iarninated with asphalt to a composition lead foil, then Iamiaiated on the foil side to a sheet of moistureproof anchored, coated, regenerated cellulose (cellophane) f i l m ? by meam of a thermoplastic coaling on the film, that provides w face t o face heat-sealed seam of sde ate strength. Section G-3 describes a solid fiber carton approximately 5-ga%loncapacity. The bag is placed in an envelope, the envelope in a carton, and two cartons in a solid wooden boxl secrirely fastened by the strap iron or wire bands. The complete pctclwge dis~ will ~ bea packed t e in~ places 1.32 cubic feet. ~ e ~ ~foods the manner described above for overseas shipment. ehydrated apple nuggets, anions, cabbage, carrots, tomato juice cocktail and cranberries are still being tentatively packed in cans; the apple nuggets and o n i o n ~En 5-gallan square cans or round steel cans, or in 363-pound frozen egg or
fruit cans; the c f e h y ~ r ~ ~cabbage ed and carrots in siar3ilar em@,in which sir has been replaced by 8nitrogexl. or 9:m;ron dioxide gam; dehydrated torneeto juice cocktail in No, 1.0 e&nB,3pounds l'0 the can; ciehydrated cranberries, powdered, in %-pound mmitavy cans. The specifications on sll of these i t e m i s flexible MO B~Bto permit the consideration DP use of prohtiiiely coated sjteei plate instead of tin pEate. . The packaging trends during the preaen-t emer none too well deEnecW for B year at least, and &re a t the moment being greatly influenced by Conservation Qrders of the WPB. T h e trends will perhaps be less well defined. in packaging for civilian^ h n for Lease-Lend or the armed forces because of the great difficulty thclt container S X ~ ~ fseturers wilil experikace in securing priorities sinfficientIy high for materials that have been c o ~ i m d used y in @hepast. The problems of packaging for dornestic cvnsilrnptiora &Ewa ~ o ~ s ~ d ~from r a bthose ~ y in ~ a for overseas ~ shipxnent. ~ ~~~~~~~~~~
U -
a
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cited
(1) Bates, A. s., Am. Brewsr, 75, No. 1,19 (1942). (2) Chem. dr~dus&ries, 51, 103 (19421). (3) e)ruo T m d e NevJa, 17, 1\90. 12, 1 (19&$. (4)Pocd MaCel.iala, 2, No. 1,4 (1942). ( 6 ) Glass Packer, P I , 423 (19429, (6) Betbbard, D, M., @amnP,r,95, No. 3 , 20 (1942), ( 3 ) Xtallie, P.E. van, DWQ T m d s Newe, 17, No. 32,29 (1942) (8) 'Tanssen, F., Qlaak Pceekar. 21, 368 (1942). (9) Lusok, R.R., Food ImctU8tTi@ri, 14,No. 8,57-63 (XQ42). (10)Ship&g ~ ~ 7 , No. 8 , %&lI ~ (1942).~ ~ (1I9 wefit5rn canasr 6% Rae.ker, 34, No. '9, 32 (1942:
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de: of carcass beef. Best results are sbtaine of dehydration equipment, incl have been used. Factors affecting the rate of drying axe discussed.
MALL quantities of dehydrated beef were produced during the first World War and subsequently for several arctic expeditions. Recently, because of the meed to conserve shipping space, renewed interest has d ~ e l ~ p ein c fthe dehydration of large amounts of meat for overseas shipment. Early in February, 1942, officials 012 the United States Department of Agriculture indicated that the Federal Surplus Commodities Corporation would like to purchase considerable quantities of dehydrated meat for Lend-Lease purposes. The meat packing industry was requested t o develop methods for the dehydration of meat. On February PO, the Committee on Scientific Research of the American Meat Institute held a meeting to discuss the problem of dehydration of meat. Et was agreed that members of the committee would seek to
carry out studies in their respective laboratories, and that the committee would ~ e e subsequently t snd e x c h a informa~~~ tion. Intensive studies of methods 0% meat dehydration were carried out by the research ~ a b o r ~ ~ oofr B number of meat tory of the American Meat ~ ~ t ~ t uand t e the , United Skates Department of A g i culture. On the basis of these studies methods have been worked out which will produce s a t ~ s ~ a c ~ and ory a c ~ e p ~ a b ~ ~ purpose of dehydrated meat is threefold: p r o d ~ c t ~The . T o conserve shipping space, to conserve tin and other s t r a t e ~ j ~ metals if possible, and to furnish a meat product which can be stored safely without refrigeration under varying ~ o n d ~ t ~ ~ ~ of temperature and humidity and for prolonged periods.
January, 1943
INDUSTRIAZ AND ENGINEERING CHEMISTRY
41
rancidity of the fats and hydrolytic splitting of the proteins. If the temperature i s reduced further so that the product is frozen and if it is then dried in vacuum, a product may be obtained which rehydrates satisfactorily and resembles fresh meat closely. The rate of drying is slow and the cost of the equipment relatively high. When raw meat is dehydrated in the frozen condition, the fat- and protein-splitting enzymes are not destroyed. Data are not available to show that meat dehydrated in the frozen state will keep satisfactorily for long periods when stored without refrigeration. Precooking may be carried out in an open steam-jacketed kettle equipped with a stirrer. The meat is cut into approximately 2-inch cub- and precooked with little or no added water. During cooking in an open kettle the moisture content of beef may be reduced from 70-72 per cent to around 50-55 per cent. After cooking, the product is ground in a food chopper Dehydrator Used b y Swift & Company equipped with a 1/4-l/s inch plate. All of the juices are retained in the ground prodThe long tube revolves with the meat inside it, resting on louver plates running uct. Precooking may be carried out in a lengthwise of the interior. Air under controlled temperatures is admitted pressure cooker. Thep the juices are added beneath the louvers and penetrates the meat evenly so that the latter, perfectly back to the ground product before i t is dried down to 5 Der cent moisture content, sifts out of the far end of the machine dried. Federal specifications require the into sanitary metal trucks. beef to be precooked a minimum of 30 minutes at not less than 165" F. internal temperature. A third method of precooking consists in putting the meat By compressing dehydrated meat with pressures of 1500 to through a meat chopper with 5 ll/a-inch plate and then 2000 pounds per square inch, the shipping space required may passing it over a steam-heated drum dryer similar to those be reduced t o less than one tenth of that required for shipformerly wed extensively for drying milk. The drums are ment of carcass beef. Boneless beef requires about 36 per set about 0.1 inch apart, and the product is cooked for about cent of the space of carcass beef. Dehydration reduces the 50 seconds. The partially dried chips are then dried in an space required to about 16 per cent, and compression of the air dryer. This results in larger sized particles. dehydrated beef further reduces the space to about 10 per In addition to increasing the rate of diffusion of moisture cent. Thus one ship will carry the dehydrated meat equivafrom the interior of the meat particles during drying, the prelent to ten shiploads of carcass beef. cooking, if carried out in an open kettle or drum dryer reduces Good quality dehydrated meat reconstitutes readily when the moisture content of the meat. The precooking also inwater is added. When cooked it compares favorably in apactivates enzymes and destroys nonspore-forming pathogens pearance, texture, and flavor with cooked, chopped, fresh if any are present. meat. The product is suitable for use in various dishes, After precooking, the product is dried promptly to a moisamong which are meat loaves, patties, croquettes, soups, and ture content of not to exceed 10 per cent in any particle. The meat pies. To be satisfactory, dehydrated meat must not precooked product should not be held for longer than 2 hours deteriorate in storage and should retain as much as possible a t a temperature within the range of 60' to 160" F. in order e0 of the nutritive value of fresh meat. prevent the development of food spoilage organisms.
Precooking of meat
Best results are obtained by precooking the beef before drying. Thin strips of raw beef have been dehydrated by warm air drying processes without precooking. When the meat is not precooked and is dried in warm air, the finished product does not reconstitute readily when water is added. In raw meat the rate of diffusion of water from the interior of the meat particle to the surface is much slower than in cooked meat. The surface of the particle will dry out and caseharden. A much longer period is required to dehydrate the meat. If the air temperature is kept sufficiently low to prevent casehardening, the drying period is greatly lengthened and suitable conditions for the development of harmful bacteria may prevail. If the temperature is reduced just below the point at which harmful bacteria will grow, the time required for dehydration will be still further lengthened. The long period required for dehydration under those conditions is sufficient to promote
Dehydration equipment Many different types of dehydration equipment have been proposed and tried. They include various types of warm air dryers, vacuum dryers, drum dryers, and gas dryers. For large-scale and efficient operation the continuous system of drying is desirable. It has many advantages over the batch system. The continuous system is more economical because it requires much less labor. Also, since there is less human handling of the product, there is less opportunity for contamination with food spoilage organisms. AIR DRYERS. Satisfactory produch have been made with the tunnel and rotary types of warm air dryers. One of each of these types will be described in more detail later. R ~ T A RDRUM Y DRYERS. Drum dryers of the type formerly used extensively for drying milk have been tried experimentally to dehydrate meat. The f r a h meat was first cooked in a ateam-jacketed open kettle and then ground through a meat
air dryers have been produced experimentally in air-conditioned smokehouses. The fresh meat was precooked in a steam-jacketed open kettle and subsequently ground in a meat chopper equipped with a 3/1&n~hplate. The product mas then dried on trays in the smolrehouse without the use of smoke. This process has the serious disadvantage of the batch process. The labor costs modd doubtless be much higher than in a continuous process.
FRESH PORK B O N E-l N PORKCUTS
.
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~ ~ f ~ f %he ~ e f drying ~f ~i rate ~ in~ais~ Dehydration of mest in B moving current of warm air, from. the viewpoint 0% the material, represents evaporation of moisture from a complicated systemi. Initially the rate of removal of water should be similar to that of an equivalent surface of water containing the same solutes. The rate is determined by the difference in water potential between the surface of the meat particles and the air and by the rate of diffusion of the moisture into the surface !ayere As long as there is rapid diffusion and t.he surfaces of the particles remain wet, the temperature of the meat particle will. not rise above that of the wet bulb temperature of the air and may be far below that of the dry bulb temperature. For this reason the air temperature, during the early stages of drying, may safely be much higher than the temperature which would injure the meat, provided there is adequate circulrttion of air. Since diffusion of moisture from the interior of the paTticle becomes a limiting factor in the later stages, the safe air temperatures in the final stages BTB much lower than in the initial stages of y precooking %hemeat, the colloidal properties of roteins are altered and diffiasion of moisture to the surface of the particle is greatly accelerated. Drying temperatures should be as high a~ possible to increme the thermal efficiency of the process and to reduce the opportunity for bacterid development, but not BO high as to injure the quality cf the product, In general, lower drying temperatures will yield a product of better quality if the drying time is not prolonged. Temperatures above 150' F. may result in some deterioration in quality akhough products of good quality have hem produced. with final drying temperatures from lS0' to If%" E'. educing the size of the particle increases the rate of drying, due to the increased surface and the shorter distance of ~
n DEHYDRATED
Space 1s Saved by Swift B
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Mefhods e%
Processing Pork
Fresh pork sides were sent io Europe during the first World War. Ten ships loaded with sides, kept under refrigeration, were re. placed early in the present war with 7.5 ships carrying the same amount of meat in special packages of bone-in cuts also refrigerated. Dehydration of the pork has cut the space requirements for the same amount of meat 20 1.85 ships. The compression packing methods cut the requirement to 1.3 ships. Dehydrated meat keeps fresh on long ocean voyages, when properly packaged, without refrigeration.
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chopper equipped with a 3/16-inchplate. The ground product was then passed over the steam-heated drum dryer. The dehydrated products consist of thin flakes. The product is more dificult t o compress into compact blocks than when dried in sir dryers. Although the drum-dried product is fairly satisfactory, i t is not 50 good as those dried in air. VACUUM SHELF DRYERS. Experiments With. Vacuum shelf dryers have demonstrated that a good quality of dehydrated beef can be produced by this method, Fresh beef chucks were ground through a meet chopper equipped with a 8/1&ncfi plate. The ground meat was cooked (without the addition of water) in a steam-jacketed kettle equipped with a mechanical stirrek. The product was brought Lo i65' F. and cooked a t that t e ~ ~ e r a tfor u ~31e9 minutea. During the cooking the product, which originally contained about 68 per cent mnisture, lost 25 per cent of its moisture. After cooking, the meat was dried in a vacuum ahelf dryer in a 4-hour cycle from loading $0 unloading. The temperature of the dryer &elf ranged from 166" to 185" F. A 29.5inch vacuum was used. The temperature of the meat ranged from 55' to 160' F. during the drying. The final product contained about 30 ger cent fat and 8.5 per cent moisture. V ~ c ' u nMELTEBB. ~ Vacuum steamjacketed meiters of the type used for rendering lard have been used experimentally t o dehydrate beef, The beef is cut in snail piecess, placed in the melter, and precooked under 9. Rotary meal cutter pressure. Then the vacuum is applied and 2. @oekkng;ikettle the product is dehydrated. T 3. Receaarer ct is in a finer state of subdiv 4. Xelicd conveyor avor is not so good as that which is prop5. Grinder 6. DryeP. erly air-dried. 7. Truck AIR-CQNDITIOMED sMBKEHOWSES. De8. Juice receiving pan hydrated beef and pork comparable in 9* ntsifuge 10. ~e~~~~~~~liquid pork fat quality to the products produced in warm
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juice receiver
Juice transfer pump Stsarn-]aoketed ]uice-holdlnq katfle
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holding ket
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16. Mixer 17. Truck $8. Steam condenser and pump
January, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
49
diffusion of moisture from the center of the particle to the surface. Another important factor affecting the rate of drying is the velocity of the air. High velocities increase the rate of drying. If the air is driven through a bed of the granular material, the depth of the layer of meat will affect the velocity of the air. After the meat is partially dried, the bed is more porous and an equal load will offer less resistance to the current of air. The effect of air velocity on the rate of water loss is more marked during the initial stages of drying, since diffusion of moisture from the interior of the particle becomes a limiting factor in the later stages. The amount of fat present influences the rate of drying. I n the initial stages the effect is not marked, but in the final stages high fat content retards the rate of water loss markedly. The higher the fat content, the earlier in the period of drying it begins to retard the rate of drying. This may be due to the fact that, after the early stages of drying, the temperature rises high enough to melt the fat. The melted fat then covers an increased surface and retards evaporation.
F. S. C. C. specifications for dehydrated beef The lgricultural Marketing Administration of the United States Department of Agriculture announced on July 1, 1942, that offers would be received for sale of dehydrated beef. The specifications given in Form FSC 1719, Dehydrated Beef-Offer of Sale, Program GCP, are as follows: SPECIFICATIONS: Dehydrated beef shall consist of beef derived from the entire carcasses of boned cattle of U. s. canner grade or better. Meat from bulls shall be excluded. Closely trimmed beef cheek meat and beef head meat may be included up to 3 per cent of the total meat used. The meat shall be rewonably free from blood clots, bruises, stringy fibrous tissue, tendons, and sections of large blood vessels. Fat content of the finished product shall not exceed 30 per cent. Salt may be added to the meat to the extent that the finished product shall average not more than 3l/2 per cent sodium chloride. The meat shall be precooked a minimum of 30 minutes at not less than 105' Fahrenheit internal temperature. After precooking, promptly dry the meat until the moisture content of the dehydrated meat product does not exceed 10 per cent in any particle when placed into the container. The dehydrated beef shall be packed as tightly as possible into rectangular or round tin cans, hermetically sealed with or without vacuum and shall be packed into containersmeeting the requirements of Federal Specifications for canned meat for export.
On July 30 the Federal Government awarded the first contract for 80,000 pounds of dehydrated beef.
Commercial processes Two types of continuous drying equipment have received prime consideration for commercial operations. One is a rotary type dryer and the other a tunnel type with an endless belt conveyor. Both types use steam radiators for heating the air. At least 80 pounds steam pressure is required for the rotary dryer. Higher steam pressures are desirable for both types of dryers although the tunnel dryer may be operated with 10 pounds exhaust steam. ROTATING DRUMDRYER.The fresh beef is passed through a rotary meat chopper which divides i t into approximately 2-inch cubes. The meat is then dropped into an open steamjacketed kettle, equipped with a mechanical agitator and having a capacity of 1500 pounds of chopped meat. Four kettles are needed to supply one rotary dryer (7 feet 11 inches in diameter and 24 feet long) having a capacity of 1000 pounds of finished product per hour. Just sufficient water is added to prevent sticking of the meat to the kettle, and the beef is then cooked with constant agitation a t a temperature not lower
Reduction in Volume Achieved b y Dehydrating Pork: the Twenty-eight Cans Hold AII fhe Meat of the Two Pork Sides, Which Dress Out fo 169 Pounds
than 165°F. or higher than 175' E'. for not less than 30 minutes. The precooking reduces the water content of the beef from about 72 to about 50 per cent. It is necessary to reduce the moisture content of the meat to 50-55 per cent of moisture in order t o dry it in the rotary dryer. The cooked product is then dropped into a steam-jacketed hopper and conveyed mechanically to a meat hasher where it is ground with '/rinch plates and a t a temperature of approximately 155" F. The precooked beef is fed directly from the hasher into the rotating drum dryer. Air heated to about 300" F. is passed through the horizontal drum dryer a t a velocity of about 800 feet per minute. The drum dryer is equipped with louver-like vents. The rotation of the drum tumbles the meat as it passes through the dryer and permits the air to pass through the tumbling mass of meat. The meat reaches the outlet end of the drum in about 2 hours with a moisture content of 10 per cent or less. The air discharge temperature is about 150" F. The product is then pressed in airtight containers and sealed under vacuum. TUNNEL BELT CONVEYOR DRYER.This dryer is built in units 6 feet long. Ten units have an estimated capacity of 1000 t o 1300 pounds of dehydrated beef per hour. The length of space required for the installation may be reduced by placing five units directly above the other five units. Each drying unit is equipped with a centrifugal fan. The equipment is designed to permit the desired amount of recirculation of air. Air velocities through the meat of 200 feet per minute are obtained. Each of the two five-unit sections is equipped with a perforated metal plate sectional conveyor which is 10 feet wide. The purpose of the two-stage drying is to maintain an increased drying capacity through a more advantageous depth of loading. The wet material containing about 55 per cent of moisture is loaded to a depth of approximately 1.5 inches, equivalent t o 2 pounds of meat per square foot, in the first stage. It leaves the first stage and enters the second stage a t about 34 per cent moisture, where the depth of loading is increased to 4.5-5 inches, equivalent to 9.5 pounds of meat
(34 per ceaat lraoisture content) per square foot, A greater depth of loading is possible in the second sta penetrates the meat more resdily after the dried. Circulation and penetration of the air through the meat is aided by B constant static pressure of 0.6 inch in both stages. The precooking and handling of the meat prior to drying i~ similar to that described for the rotary dryer. If desirable, products containing more moisture can be dried in this type of dryer than in the rotary dryer. The precooked chopped meat is fed onto the belt C Q ~ W ~ ~ Qby I - means of an autometio oscillating conveyur which deposita the meat at a uniform depth. Tests made on meat dried ~ x p e r ~ m ~on n tboth a ~ ~types ~ of equipment indicate that ~ e ~ ~meat ~ of ~ equal e t quality e ~ can be made with either type of equipmentb
Federal oEeialrs have ~ w ~ ~ cthat ~ t eonly d limited of beef will be d e ~ y ~ r aPlans ~ ~ o ~ ~ tities of ~ ~ h y ~ program has been o increase capacity to
beef appear to be s u for pork. ~ However, ~ ~ ~ ~ higher fat content nand the ~ ~ f f e r ine physical ~ c ~ ~ ~ ~ aof ~ pork tissues, diome ~~~~~~~~~o~~ ay be ~ e c e ~ s ~Itr may y~ be necessary to remove some of the fat in the proceas of pre-
~ ~ o The ~ precoo ~ n ~ period . may require a longer time. ~ x ~ ~indicate r ~ ~ after e ~ t ~ the product may precooking, be pressed to remove fat and moisture. After the fat is skimmed off, &hewater extract may be concentrated i n L vacuum evaporator to B sirupy con&stency. The ~ ~ A R R residue may be ground tPL1rough y1 hsaher and dried. The ha h or at^^ ~ i r n pis then added $0 the dried resicimc. C n this ~ ~ B finished ~ prodrrct ~ may c be produced ? ~ containing nbout BO per cent protein, 40 per cent fat, Pand about 1.0 per oeni moisture:. ufficient data w e not available t o KEEPIN@ $UAEBTY. indicate how P,aag ~ e ~pork ~will keep. ~ ~ Experimentn ~ , indicate that dehydrated beef wili not become rancid for long the produot is packed tightly in hermetically sealed It may be nc?oesssry to pack dehydrated pork uum br to me a ~ t ~ o in~order ~ ~t oaprevent ~ ~ ~ r m soidity,
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have shown that from a baoterioed meat made in accordan(:e WitJh is safe and \Vila remain so lvhear
vsloped and proved ~ ~ it will be necessary t t~ o USA metal ~ t o test the ~ keep-~ ~ cam. Intensive ~itudieeare ~ beef and pork w h e n packed in vsriing ~ quality t ~ of e dehydrated ~ o w metallic anid ~ ~c~ntalners ~and subjected ~ t o widw~ ~ ~ r ~in ~ e t~ ~~ ~~ ~ eandrshumidity, ~ t u r ~
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H.s. MITCHELL AND H.c.B CK,Swift B Company, Chicago, 111.
hyedw ana ketone5 are p ~ d u c e dtag. rupture the ealboe eo to which the reaction st the oxidiae$ %aonas. in an oxidative deterioration known as rancidity. Only has progressed determines t of the spoiiitge. 'I'heros meager information exists on the reactions that take i5 B latent QF induction period of variable en^^^ during which place, It is well established that they are autocatalytic in nature. They are accelerated by heat, light ~ e ~ p e ultrac ~ a ~ BSnSrll ~ ~ WAOuntS 0%oxygen &Eabsorbed BBd only slight Orga7lo%opticchanges are noted. This b followed by a rapidly a@viobet), and metals such as iron and copper and their ealts. celerated oxygen absorption a c ~ ~ by~thepappetiranss ~ ~ ~ The rate is lowered by antioxidants. The refining procedures of the so-called rancid odors and avom The final strtge is BI i~~ to present-day necessary t o produce S h o r t e ~ acceptable breakdown of the oxidized bonds, which is accompanied by consumers remove large percentages of the natural antioxistrong acrid odors. dants, with the result that refined oils and fats exhibit less The logical means of preventing these reactions is either resistance to rancidity than do the crude materials. protection from oxygen, as exemplified by vacuum packing, Oxygen is absorbed by the unsaturated bonds of the fatty or by the use of antioxidants. The former involves considermids, with formation of peroxides, and finally certain aide-
ATS and fatty foods are: attacked by oxygen, resulting
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