Anhydrous Milk Fat Manufacture

The quality assurance program for manufacture of butter oil, or anhydrous milk fat (AMF), also focuses on the quality of the raw materials. Naturally, many of the same considerations apply to handling raw cream for AMF manufacture that apply to butter, except that vacreation is not used. Because it is stored under ambient conditions, care against oxidation is essential. Oxidation is perhaps the most important mechanism by which milk fat deteriorates in quality. Because the oxidation reaction is autocatalytic (ie, the products of the reaction act as catalysts to promote further reaction), the normal quality control tests, peroxide value and free fat acidity, could give misleading results when applied to stored butter. Methods of deaeration have been developed that could reduce potential oxidation (24).

Milk fat is present in milk or cream as part of a stable oil-in-water emulsion. The emulsion is stabilized as a result of the protein and phospholipid-rich milk fat globule membrane (MFGM) surrounding the milk fat. During AMF manufacture the aim is to break the emulsion and to separate out all of the nonfat solids and water. To achieve this, the MFGM must first be disrupted mechanically or chemically. Homogenization, an example of mechanical treatment, disrupts the membrane, destroying the membrane layer. For chemical destruction of the membrane layer, an acid such as citric acid can be added to lower the pH of milk or cream to about 4.5 (60). The protein will precipitate, removing a component to maintain an intact fat globule. Direct-from-cream AMF plants usually has three separators. The first concentrates cream from 40% to about 75% fat before phase inversion in a homogenizing device. The oil separator then separates the liberated butter oil to about 99% purity. The oil is washed with water before the third (polishing) separator and the final traces of moisture are removed in a dehydrator at 95°C and under a vacuum of 35 to 50 torr. The dehydrator is usually a simple vessel, and the butter oil is introduced either as a thin film on to the walls or as a spray, to maximize the surface area exposed to the vacuum. Such a device will not remove significant off-flavors, because the vapor flows, temperatures, and pressures are inappropriate for flavor stripping. When producing AMF from butter, fresh or block butter is softened just to a pumpable stage (approximately 50°C) and transferred to a plate heat exchanger to increase the temperature (70-80°C). The oil phase is concentrated through separators and dried under vacuum. Some washing is possible before the final separator removes the last traces of nonfat components (60).

In terms of the preparation of products and their appearance and texture, AMF has several advantages over traditional butter. The latter is in fact subject to seasonal variations, which affect its physical properties. The advantages of AMF are linked to the possibility of standardizing its physical properties (by the selection and mixture of the raw materials used in production) and the possibility of adapting its properties using the fractionation technique.

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