Concentrated and Dried Milks Is About 2Vo Billion Pounds
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Concentrated and Dried thai left from the separation of milk for cream and butter, also goes into manufactured milk products. The fluid milk (equivalent utilized in the Milk production of the concentrated and dried milks is about 2vO billion pounds. B. H. Webb Approximately 6/2 billion pounds of milk is made into evaporated milk each year, and 280 million pounds is canned as sweetened condensed milk, both largely for household use. The ice- The concentrated and dried milks cream industry uses a]:)out 3 billion are manufactured to conserve fluid ]:>ounds of skim-milk concentrates to milk for use where fresh milk is scarce build up the nonfat milk solids of ice and during seasons of low production. cream. The manufacture of foods other Specialized knowledge and equipment than dairy products requires prepa- enable processors to manufacture the ration of milk concentrates from 4 bil- difièrent concentrated milks by remiov- lion pounds of milk. About one-third of ing part of the water from the milk. the production of concentrated and The products are the source of concen- dried milks is used in beverage milks, trated milk soUds needed for the prep- cottage and other special cheeses, malt- aration of many foods, both in the ed milk, and animal feeds. home and in the food factory. The names assigned by custom to the SWEETENED CONDENSED MILK is concentrated milks have confused the manufactured by a few simple but vital layman and provoked the etymologist. operations. Harmful bacteria and en- Plain condensed whole and skim milks zymes are destroyed by fore warming. contain no sugar and are perishable In that treatment, the milk is heated to products. Sweetened condensed whole about 185° F., which helps also to and skim milks are preserved by the control thickening of the finished milk addition of sugar. Evaporated milk is during storage. The hot milk is drawn not sweetened; it is sterilized in cans. into the vacuum pan—in which milk Dried milks may be either dried whole boils at temperatures as low as 100° F. or dried skim milk^ except that Con- and water is rapidly removed without gress in 1944 amended the Food, Drug, coloring the milk or giving it a cooked and Cosmetic Act by providing a stat- flavor—together with 18 pounds of utory definition for dried skim milk sugar for each 100 pounds of milk, A under the names "nonfat dry milk sirupy milk, which tastes delicious, is solids" and "defatted milk solids." drawn from the vacuum pan and Nearly half of the 120 billion pounds cooled with continuous agitation. Tiny of milk produced annually in the crystals of lactose (milk sugar) grow United States is consumed as market spontaneously when the condensed milk and cream. From the remainder milk is stirred at about 85°. Improper (except the milk used on the farm), cooling causes the growth of large, such dairy products as butter, cheese, coarse crystals that make the milk taste ice cream, concentrated milk, and sandy. Sweetened condensed milk is dried milk are manufactured. Fifteen packed in cans or barrels. When held billion pounds of skim milk, part of at 70° for 6 or 8 months, the product 690 CONCENTRATED AND DRIED MILK 691 darkens and thickens. The change can and the persistence of good viscosity be greatly retarded by storing it beiow and body characteristics during stor- 60°. Sweetened condensed milk retains age if the solids content were raised to its acceptable condition for at least a 28 percent. year if held at a low temperature. It is Small crystalline particles, about the not damaged at temperatures well be- size of the head of a pin, sometimes low 0° F. because of its high sugar appear in stored evaporated milk. They content. are complex milk salts that have crys- Perishable concentrates, produced tallized and settled to the bottom of the and packaged in bulk for food proc- can. The conditions governing their essors, are called plain condensed milk. separation are little understood ; hence They contain no sugar and must be their formation cannot always be pre- held under refrigeration. The manu- vented. Salt crystals in evaporated milk facturing process consists simply in are not harmful, but sometimes they heating, condensing, and cooling the are an annoyance, especially when they milk. obstruct the holes in nijDpk^.s of babies' bottles. EVAPORATED MILK, unlike sweetened Bureau of Dairy Industry chemists condensed milk, contains no added have studied evaporated-milk salt crys- sugar. Spoilage is prevented by sterili- tals. The crystals are composed largely zation with heat. Steps in the manufac- of calcium citrate, with traces of phos- ture of evaporated milk arc: Fore- phates. Crystals generally do not begin warming, evaporation, homogeniza- to appear in the milk until it has been tion, standardization, canning, and in storage 6 months or more. They sterilization. grow more rapidly when the evapo- The time and temperature of fore- rated milk is held at room temperature warming affect the stability of the milk than when it is stored at 60° or below. toward heat and the viscosity, or body, The formation of crystals can be ac- developed in it during sterilization. celerated by adding calcium chloride Forewarming is generallv done at a and sodium citrate or by lightly seed- temperature of 190° to 212° F., de- ing the milk with calcium citrat(\ pending on the condition of the milk. Early in the Second World War the Dairy scientists recently investigated Governrnent had to store much evapo- the effect of forewarming milk to tem- rated milk. Some of it, after being held peratures up to 300° on its heat sta- for 2 or 3 years, showed citrate crystals, bility and viscosity. They found that a thinning in body, and some separa- milk fore warmed at 250° for 3 to 4 tion of fat and protein. Dairy scientists minutes attained a much greater heat knew that evaporated milk was a re- stability than when temperatures below markably stable product; they deter- boiling were used. The discovery en- mined nevertheless to find a way to ables manufacturers to raise the solids increase that stability. They found that content of evaporated milk without en- the magnitude of the storage change countering coagulation difficulties dur- depended partly on the temperature. ing sterilization. Evaporated milks have Below 60° F. changes were slight, but been made with a solids content up to above 90° the product deteriorated 38 percent. noticeably in a few months. It was Storage t(^sts on milks containing found advisable to hold evaporated various percentages of solids, however, milk at a temperature not to exceed have shown that the best milk is pro- 75° and to turn the cases every 6 weeks duced when the solids are held within to retard fat separation. the limits of 26 percent to 32 percent. Fat separation in evaporated milk The present evaporated milk with a depends not only on the efficiency of solids content of 26 percent would be homogenization, on viscosity, and on improved in terms of nutritive value conditions of storage, but also on the 6^2 1950-1951 YEARBOOK OF AGRICULTURE Approximate composition, degree of concentration, and density of mille and concentrated milks Milk Degree of solids Pro- Milk Su' concen- Density Product Water not fat Fat tein sugar Jsh crose tration at 60" F. Per- Per- Per- Per- Per- Per- Per- Specific cent cent cent cent cent cent cent Ratio gravity Milk 87.0 9.1 3.9 3'S 4.9 0.7 1.032 Skim milk 90. 5 9.4 .1 3-5 5.1 1.035 Evaporated milk 73 «7 18.4 7.9 7.0 9.9 1.5 2.02:1 1.066 Plain condensed whole milk. 64.0 25.2 10.8 9.7 13.6 1.9 2.77:1 1.095 Plain condensed skim milk . 70.0 29.7 •3 II. I 16.1 2.5 3.15:1 1.125 Sweetened condensed whole milk 28.0 8.5 7.7 10.7 1.6 43.5 2.20:1 1.266 Sweetened condensed skim milk 28.0 29.7 .3 16.1 2.5 42.0 3-15:1 1.366 Dried whole milk 3.5 69.8 25.8 38.0 6.0 7-5o:i .550 Dried skim milk 2>-í 95.5 I.o 3S'(> 52.0 7.9 ....... 10.20:1 ,600 physical state of the protein that is as- civilian use, although canned chocolate sociated with the fat in the cream milk is available in some markets. layer. Easily dispersed fat layers are less objectionable than layers that are DRIED MILK w^as one of the chief con- held tightly together by adsorbed, tributions of the dairy industry to win- partly denatured protein. Causes for ning the Second World War. Before the gradual changes in the milk pro- the war the production was largely tein during storage of evaporated milk dried skim milk and dried buttermilk, are still being investigated. both byproducts. During the war a A new canned flavored milk that is great demand for dried whole milk high in energy value and suitable for prompted a sevenfold increase in its drinking directly from the container manufacture. The dried milks are now was developed by scientists in Govern- made by three principal methods, usu- ment and industry in response to re- ally designated as spray, atmospheric- quests by the Army Quartermaster drum, and vacuum-drum processes. Corps. The milk was wanted for use In the spray process, partly concen- on invasion beachheads, where the trated milk is sprayed by pressure or landing forces frequently needed centrifugal means into a chamber quickly available nourishment.