The coagulated mass is next cut using harp-like, wire knives that cut the curds into die-sized particles. The knives are constructed such that the curds can vary in size. Since this step is performed to enhance syneresis, the size, or more importantly, the surface area of the curd particles, has a major influence on the rate of water removal from the curd. Hard, low-moisture cheeses like Parmesan and Swiss are typically cut into kernel or wheat berry-sized curds, whereas soft, high-moisture cheeses are cut into die-sized pieces. The size of the curd also influences fat loss—more fat is retained in large curds than in small ones. Regardless of the size of the curd at cutting, the actual composition varies relatively little.The curd is constructed of a calcium-casein complex that contains entrapped fat and bacteria (including starter culture organisms), as well as water and water-soluble components including whey proteins, enzymes, vitamins, minerals, and lactose.
Syneresis begins as soon as the curds are cut, and increases during the ensuing minutes when the curds are gently stirred. The initial rate depends on the starting pH of the curd, because prior acid development greatly enhances syneresis. However, the cooking step is the primary means of enhancing syneresis. All other factors being equal, the higher the temperature and the longer the curds are cooked and stirred, the dryer will be the finished cheese. Thus, the cooking step is one of the major variables that cheese manufacturers can manipulate to produce different types of cheese.
As noted previously, the more water removed from the curd, the less lactose will be available for fermentation. Cheese manufacturers can, therefore, influence acid production and cheese pH by modulating the cooking time and temperature conditions. Whatever the cooking temperature, however, the culture must be able to withstand that temperature, or else the cells will be attenuated (or worse yet, inactivated). Furthermore, when heat is applied it must be done gradually via a step-wise progression, since too rapid heating causes the exterior of the curds to harden and actually reduce syneresis. The cooking and stirring step has so much of an effect on the finished cheese that some experienced cheese makers can tell how dry the cheese will be simply by touch and the feel of the curd. Of course, some soft cheeses, like Brie, are not cooked at all, but rather are stirred at the setting temperature. Finally, although the actual heating step usually occurs via indirect heat transfer through jacketed vats, it is also possible to inject steam directly into the whey-curd mixture.
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