The curd contracts and hardens during this process, and soon reaches a condition when the surface does not adhere so readily. The vat should be kept warm during the process of separation of the whey, the temperature being raised to about 90 degrees and finally, toward the last, to 98 degrees, about blood heat. _Separating the Curd._--The precipitated curd is left in contact with the whey for some time, and during this period some of the lactic acid in the whey unites with the paracasein. The setting of the curd is finished when a small mass which has been squeezed in the hand to remove the whey is pressed against a bar of iron heated to little short of redness, and it is found that there is left, adhering to the iron, fine silky threads. These threads are formed by the compound of lactic acid and paracasein, and the more of this compound there is the longer will the strings be. When the curd shows by the hot iron test strings one-eighth inch long it is an index that the time has arrived for the separation of the curd from the whey. _Gathering the Curd._--After the whey is removed the cubes of curd are left in the bottom of the vat until they mat or pack together, a process which is technically known as cheddaring. The curd is sometimes removed from the vat and placed on a special apparatus for this purpose called a curd-sink. When the curd has matted together, forming a solid mass, it is cut into blocks 8 × 8 × 12 inches. These blocks are turned in the vat in order to facilitate the removal of more whey. The blocks of curd are carefully placed, one over the other until they form a large mass. The process of solidifying or cheddaring accomplishes two purposes: First, the whey is expelled to a considerable extent and, second, the lactic acid unites with more of the curd, changing not only its chemical composition but also its physical state from a spongy, tough, rubber-like consistence, with a high water content, to a mass having a smooth, velvety appearance and feeling, and a soft, somewhat plastic consistency. _Milling the Curd._--This process consists in cutting the lumps of curd into small pieces in order to introduce the salt and to handle it more readily when it is to be placed into hoops for pressing. This process is done by special mills which avoid, in so far as possible, the loss of fat.