Curd handling

Perhaps the most influential step during the cheese making process involves the means by which the curd is handled during and after the cooking and stirring steps. For many cheeses, the whey is removed when the desired acidity is reached, when the curd has been cooked for a sufficient length of time, or when it is sufficiently firm or dry. There are several means by which the curd is separated and the whey is removed. In traditional Cheddar cheese manufacture, the curds are simply pushed to the sides of the cheese vat and the whey is drained down from the center, with screens in place at the drain end to prevent curd loss.Alternatively, the curds can be collected in cheese cloth and hoisted above the whey, as in traditional Swiss cheese manufacture.In more modern, large production factories, where cheese vats must be cleaned and re-filled, curds and whey are typically pumped to draining tables or Cheddaring machines, where whey separation occurs. Similarly, the curd-whey mixture can be added directly into perforated cheese hoops, where the whey drainage step is completed.

Although there are many ways to manipulate the curd to alter the properties of the cheese, one simple twist in the separation step is worth special mention. If, during the draining step, water is added back to the curds, then so-called "sweet" or low-acid cheeses will result. This is due to lactose dilution. Since the lactose concentrations in the curd and whey are ordinarily in equilibrium, when whey is removed and replaced by water, lactose will diffuse from curd to water, leaving the curd with markedly less lactose available for subsequent fermentation by the starter culture. Thus, the initial pH of Colby, Gouda, Havarti, and Edam cheeses are generally in the range of 5.2 to 5.4. If the added water is warm (i.e., about 35°C ), cooking and syneresis will continue (as is the case for Gouda, Edam, and Havarti). However, if the water is cold (about 15°C), the moisture content of the cheese may increase (e.g., Colby).This washing step is also used for Mozzarella, in part for pH control, but more so to remove lactose and galactose from the curd (discussed later).

Once the curds are separated from the whey, several things begin to happen. First, the starter culture finds itself at a temperature conducive for growth, and soon the fermentation of lactose to lactic acid occurs. A subsequent decrease in curd pH and an increase in the titratable acidity (expressed as percent lactic acid) of the expressed whey is evident. The curds, almost immediately after whey is removed, mat or stick together. The matted curds, helped by piling slabs on top of one another, begin to stretch out and become plasticlike, a process known as Cheddaring. Alternatively, the dry curds can be stirred to facilitate whey removal and to lower the moisture in the finished cheese.

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