Once milk is transformed from a liquid into a solid (actually a gel), the next goal is to remove water.The first step involves increasing the surface area of the single large gel mass by cutting it into literally millions of smaller cubes of curd (e.g., 1 m3 of a cheese gel cut into 1 cm3 particles yields 106 such curd particles). Because the distance the water molecules must travel (from the interior of the gel to the outside environment) decreases as the curd size decreases, this step has the effect of substantially increasing the rate of syneresis. Then, when these curds are stirred, and then heated, the curds shrink and syneresis is further enhanced.
Acidification is another factor involved in concentrating milk solids. As discussed previously in Chapter 4, as the pH approaches the isoelectric point of casein (i.e., 4.6), waterholding capacity decreases and syneresis, or whey expulsion, increases. In cheese manufacture, as for cultured milk products, acidification is due to fermentation of lactose by the starter culture. As we will see later, the culture performs other critical functions; in particular, it is also responsible for desirable flavor and texture properties. But it is the ability to convert lactose to lactic acid and to reduce the cheese pH that makes the culture essential. Finally, it is possible to use physical force (i.e.,pressure or gravity) to squeeze out even more water.
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