Document oMVKvYXMqeaJgnXO72vd6b2Bg

368 CHAPTER 32 1962 Guido And Data Book 1958. Over one.billion lb were exported by 20 countries thatyear. Refrigeration makes it possible to ship, hundreds of mil lions of pounds of butter per year half-way around the globe. More butter is manufactured in the United States than in any other country. One-fourth of all the milk produced in this country is used for butter. The 1780 butter manufactur ing plants made 1.3 billion lb in 1958. Table 3 shows that the plants located in the East North Central and West North ' Central states produced 87 percent of the total volume of butter. Higher sanitary standards for the production of milk on the farm and better cooling and transportation methods have im proved the quality of milk and cream now being delivered to the creameries. A larger proportion of the milk produced is now sold in the form of milk than as cream. This has had a favorable influence on the quality of the butter manufactured. COOLING CREAM AFTER "PASTEURIZATION The three billion pounds of cream pasteurized annually by the creameries in the United States and used in butter manu facture must be cooled immediately after pasteurization. The cream is commonly cooled to 40 to 45 F during spring and summer and to 50 F during fall and winter. Tap water is used first to reduce the temperature to between 80 and 100 F. Refrigerated water or brine is then used to reduce the tem perature to that desired. The cream may be cooled by having the cooling medium pass through a revolving coil in the vat or through the vat jacket, or by using either a plate or a tubu lar cooler. If the temperature of 1000 lb of cream is to be reduced by refrigerated water from 100 F to 40 F and the specific heat of the cream is 0.85, the heat units to remove would be: 1000 X (100 - 40) X 0.85 - 51,000 Bttt This heat can be removed by 51,000/144 *= 354 lb ice at 32 F plus 10% for mechanical loss. The temperature of the refrigerated water commonly mqj for cooling cream is 33 to 34 F. The ice-bank system is found very efficient lor this. Brine is not used to the extent it waa years ago. The cooling of 300 gal of cream from 100 F to 40 F can be done in a vat using refrigerated water in about one hour. After a vat of cream has been cooled to the desired teaperature it will be observed that an increase in the tempera ture takes place during the following three hours. The temperature may increase several degrees depending on the rapidity with which the cream was cooled, the temperature to which it was cooled, the richness of the cream and the prop erties of the fat. The reason for the rise in temperature is the liberation of heat when the fat is changed from a liquid to a crystal form. H. A. Rishoi has presented data1 in fig. 2 that show the thermal behavior of cream heated to 167 F, followed by rapid cooling to 86 F and to 50.7 F as compared with cream heated to \22 F and cooled rapidly to 88.5 F and to 53.6 F. The curves indicate that when cream is cooled to a temperature at which the fat remains liquid, the cooling rate is normal, but when the cream is cooled to a temperature at which some fractions of the fat are known to have crystallized, a spon taneous temperature rise takes place after cooling. The same investigator determined the amount of heat that was liberated by the part of the milk fat which crystal lises in the temperature range of 85 to 33 F. The results are shown in Table 4 and fig. 3. The data in Table 4 show that at a temperature below 50 F about one-half of the heat liberated was evolved in less than 15 seconds. The information obtained has some practical importance. The heat liberated during fat crystallization constitutes a con siderable portion of the refrigeration load required to cool fat-ricb cream. Rishoi states: "If we )**gurn< an operation of cooling cream containing 40 percent fat from about 150 to 40 F heat of crystallization evolved represents about 14 percent of the total heat to be removed. In plastic cream containing 80 percent fat it represents about 30 percent and in pure milk fat oil about 40 percent.'' CHURNING It is common practice to chum the cream during the morn ing following the day it was pasteurized. The cream is stored overnight in a covered stainless steel vat. Although many creameries still use wood chum barrels it will not be many years before metal, such as aluminum or stainless steel, will be used entirely- The metal must be sand blasted on the surface that comes in contact with the butter to prevent sticking. Metal churns are more sanitary than wooden chums and they have the advantage of permitting variety in design. They may be circular, cube-shaped, oval or cone-shaped, etc. A cream pump is unnecessary with a metal ebura because the cream from the vat can be drawn into the chum when a vacuum is maintained in it. There is the further advantage that tiie butter can be worked under a partial vacuum. This results in butter with a closer texture, a brighter appearance .paltry and Dairy Products 369 Table 4 .... Btu Liberated per Lb of Fat in Cream Cooled Rapidly from About 86 F to Various Temperatures in the 32-68 F Range . - twnpwefcw* 1r ** M obs*rrd tonpwatur** ftarf #quBbfiu hsciperahr*i lapsed time in aimutet " 0.25 60 120 180 360 33.4 F 36.2 39.3 18.3 23.6 25.5 30.4 32.4 32.9 34.0 33.6 33.6 39.6 F 43.7 46.1 16.7 20.0 23.9 27.5 29.3 30.2 30.9 31.8 32.5 53.1 F 54.5 58.0 58.0 F 58.6 60.7 63.4 F 63.8 65.3 8*v liberated per Pound 7.75 12.8 18.0 21.4 25.0 2.9 7.2 12.2 14.0 14.7 2.3 5.2 9.0 10.2 10.6 26.6 27.2 27.9 27.2 16.0 17.5 18.4 18.8 10-6 10.6 80.4 F 80.4 82.6 0 0.35 2.1 2.7 2.9 4.3 4.9 5.0 5.0 85.6 F* 85.6 85.6 0 0 0 0 0 % Heat liberated at zero compared with that at equilibrium: 54.5 51.3 27.7 20.7 21.7 Total heat liberated compared with that liberated at about 32 F: 100.0 95.7 82.0 55.0 31.0 12.5 0 Iodine values of three samples of butter produced while these tests were in progress were 28.00, 28.55, and 28.24. Cf-1*-*4 in w ice water bath. sad a lower air content than when it is worked without a vacuum. Whereas present day chums used in the United States are equipped lor two operating speeds, one for churning and one for working, the churns used in the chief butter-producing countriesofEuropepermit up tosix or eightspeeds. American chum manufacturers are now giving attention to constructing churns that permit variable speeds. The fat content of the cream churned in the American creameries generally ranges from 30 to 40 percent. For great est efficiency the fat content should range from 35 to 40 per cent The temperature of the cream should be such that an exhaustive churning can take place in from 40 to 45 minutes. It will be satisfactory to have an amount of cream in the chum that will occupy up to 40 percent of the volume of the chum barrel. The churning temperature during spring and summer gen erally ranges from 45 to 52 F and during fall and winter from 52 to 60 F. The fat in cream during spring and summer, when the cows consume green feeds, has a lower melting point than during fail and winter. The spring- and summer-produced fat - contains a larger percentage of low-melting point glycerides than fat in cream produced in fall and winter. In order to prevent fall- and winter-produced butter from being too hard and difficult to spread at home refrigerator temperature it is possible to subject the cooled, pasteurized cream to a special temperature treatment prior to churning. The resultant butter is softer and more spreadable than that made in accordance with the usual method. The buttermilk contains a small amount of fat in the form of small fat globules but this loss should not exceed one per- reat of the total fat churned. It is common in some countries where the butter is to be consumed shortly after manufacture to omit washing the but ter granules with cold water, but washing is commonly prac ticed in the United States. Water at a temperature of about .45 F, equal in volume to cream placed in the chum, is usually used. Washing consists of revolving the chum barrel con fining tire butter granules and water 12 to 15 revolutions. The water firms the butter granules slightly so that it is Possible to work them together into a mass without having tire butter become greasy. If 1000 lb of water at 45 F is used for washing the butter granules from 1000 lb of cream it will be necessary during the warmer months of the year to cool the available water to this temperature. If the water temperature is 55 F the heat to be removed is : 1000 X (55 - 45) 10,000 Btu Large creameries have specially constructed tanks for the butter wash water. The smaller plants generally use the vat