Manufacture Of Butter

Review of Figs. 1-12 will give the reader an understanding of the complete butter-making process, both continuous and batch methods. The manufacture of butter (Fig. 12) is uniquely characterized by the following three processes:

  1. Concentration of the fat phase of milk. This is done by separation or standardization of milk which results in cream.
  2. Crystallization of the fat phase. Large numbers of small solid fat crystals in globular form are required, with each globule surrounded by liquid fat. Although pasteurization of cream yields a fully liquefied

Figure 1 Continuous butter churn. (1) Churning cylinder containing beaters to break emulsion. (2) Separation section where buttermilk is drained. (3) Squeeze-drying section where initial working begins and where salt is added as a slurry. (4) Second working section where uniform moisture and salt dispersion occur and texture is finalized. (Courtesy of Dairy Processing Handbook. Tetra Pak Processing Systems AB, Lund, Sweden.)

Figure 1 Continuous butter churn. (1) Churning cylinder containing beaters to break emulsion. (2) Separation section where buttermilk is drained. (3) Squeeze-drying section where initial working begins and where salt is added as a slurry. (4) Second working section where uniform moisture and salt dispersion occur and texture is finalized. (Courtesy of Dairy Processing Handbook. Tetra Pak Processing Systems AB, Lund, Sweden.)

Figure 2 Control panel display. Control and monitoring of the churning process is affected at this point. A flow diagram through the churning process is shown. Figures 2-9 illustrate modern, high-speed, sanitary production of butter.
Figure 3 Butter is delivered from the turret end of the continuous churn into a covered silo.
Figure 4 Butter is discharged into the covered silo.
Figure 5 Butter in covered silo moving to a rotary positive displacement pump by augers.
Figure 7 Infrared light sensor (arrow) monitors level of butter in hopper and signals computer which controls off/on of delivery pump and an air-operated valve.
Figure 8 Wrapping of 1-lb prints of butter.
Figure 9 Filling of butter cups on a Form-Fill-Seal machine (Hooper Engineering, Sarasota, FL).
Figure 10 A batch churn with controls. A few batch churns continue to operate in the United States.

milkfat, cooling and tempering for at least 4 h at approximately 10°C is necessary to develop an extensive network of stable fat crystals surrounded by liquid milkfat. In making ripened-cream butter, addition of lactic acid bacteria to pasteurized cream cooled to 16°C is followed by incubation until a pH near 5 is attained. Cooling to 3-5°C stops the fermentation followed by warming to 10°C immediately before churning. This technique controls the fermentation while allowing for liquid fat on the globule exterior.

3. Phase separation and formation of a plasticized water-in-oil emulsion. Churning breaks the oil-in-water (o/w) emulsion and results in a plastic, water-in-oil (w/o) emulsion. The phase inversion occurs in both batch and continuous churns. During churning, vigorous agitation is used to disrupt the membrane on each milkfat globule. When the emulsion breaks, milkfat globules have formed pea-sized granules. Continued aggregation of fat globules forms a continuous matrix at an optimal temperature. The optimal temperature is dependent on triglyceride composition and season of the year; for example, 10°C summer and 11 °C winter (Brunner, 1976). Churning is inefficient with homogenized cream or if the milkfat is too liquid or solid (too warm or too

Figure 11 Interior view of a batch churn showing vanes on outer edge, inspection window, and center tube which can have chilled water circulated through it to control product temperature. Butter is removed by one of two ways: (a) manually with metal scoops or (b) by dumping the butter into a boat (hopper) positioned beneath the churn. The boat is then wheeled to the packaging area.

Figure 11 Interior view of a batch churn showing vanes on outer edge, inspection window, and center tube which can have chilled water circulated through it to control product temperature. Butter is removed by one of two ways: (a) manually with metal scoops or (b) by dumping the butter into a boat (hopper) positioned beneath the churn. The boat is then wheeled to the packaging area.

cold, respectively). The proper blend of liquid fat surrounding solid fat is necessary. The optimum temperature for continuous churning is from research conducted on batch churns to minimize fat losses. Continuous churn operations require similar cream conditions to those for batch churns to control fat losses to buttermilk. Using batch churns, researchers found cream must ''break'' or aggregate into pea-sized granules in 45 min to minimize fat losses in buttermilk. These same principles of operation have been used in developing butter manufacturing techniques with the continuous churn. Cream is pasteurized at a minimum temperature of 85°C and held for at least 15 s at that temperature. Research proved that high-temperature pasteurization was necessary to allow for frozen (-30°C) storage of butter for 2 years as with Commodity Credit Corporation (CCC) purchases of surplus product. Lipase native to milk, in particular, may reactivate with lesser thermal treatment resulting in spoilage of butter by hydrolytic rancidity.

Figure 12 Production of butter.

Working of butter accomplishes two purposes: first, even distribution of moisture and salt in tiny droplets, and second, to allow for fat crystal growth to increase spreadability and to minimize brittleness of the product. After churning and working, butter is salted. Salting is done near the end of working in a continuous churn and at moisture standardization in a batch churn to prevent loss of salt. Packaging occurs after salting and may be done directly into retail portions or in bulk containers (25 and 31 kg are common) (Varnam and Sutherland, 1994). National intervention boards in the European Economic Community stipulate a storage temperature of - 15°C; however, a lower temperature is frequently used, particularly for unsalted butter. A temperature of -30°C was effective for storing butter in excess of 1 year (Varnam and Sutherland, 1994). Stored frozen butter is later thawed and microfixed and then packaged into retail containers. Microfix-ing is a mechanical process that reestablishes the physical structure of butter lost as a result of freezing. Butter from different manufacturers may be blended together during repackaging. Without microfixing, butter will have texture problems (lack of spreadability) and may show moisture leakage.

Thus, butter manufacture involves partial or complete separation of cream from raw milk, pasteurization, possible fermentation by added lactic acid bacteria (when ripened-cream butter is manufactured), churning, working, salting, packaging, storage, and perhaps later repackaging (see Fig. 12). All of these activities impact on the microflora of the final product.

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