The crystal structure of fat and the resulting physical properties of butter made by both conventional and alternative processes have received considerable study. When conventionally churned or Fritz butter is made, most of the milk fat is contained within the fat globule in cream during the cooling and crystallization process. The fat globule provides a natural limit to the growth of fat crystals. Cooling and holding of cream is normally carried out overnight, and thus sufficient time exists for the crystallization process to approach equilibrium (29).

The principles of crystallization of plastic fats in the type of equipment used for margarine manufacture have been described (30). It is important to develop small fat crystals that remain substantially discrete and do not form a strong interlocking structure. Small crystals (eg, 5-//m diameter) have a greater total surface area than large crystals and will bind water and free liquid fat by absorption more effectively (29). Large crystals impart a gritty texture to the product. When fats are cooled rapidly in a scraped surface heat exchanger, fat crystallization commences, but the fat is substantially supercooled on exiting. If crystallization is then permitted to continue under quiescent conditions, crystals will grow together and form a lattice structure. The product will thus be hard and brittle and may tend to leak moisture. If, however, crystallization is permitted to occur under agitated conditions (eg, for 1-3 min in a pin worker), the formation of small, independent crystals will be favored and the product will have a fine, smooth texture. If crystallization under agitated conditions is permitted to continue for too long, the product will be too soft for most patting or bulk filling operations, and it is likely to be too soft and greasy at warm room temperatures.

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