The proper time to "mill" the curd is determined by its physical condition. Some curds will cheddar much more rapidly than others, hence no definite length of time can be given. Curd, when ready to mill, should have a fibrous texture somewhat like the white meat of a chicken breast. The pieces of curd should split very easily. When cut, the curd should show a close, solid, smooth interior. The amount of lactic acid developed may vary within rather wide limits. The hot iron may show strings ½ to 1 inch long. The acidity (by titration of the freshly separating whey) may be 0.45 to 0.65 of 1 per cent. If the curd has been properly made, that is, firmed up in the whey with the proper acidity so far, acid development during the cheddaring process will take care of itself. The physical condition remains the principal means of determining the time when the curd should be milled. [Illustration: FIG. 39.--Gosselin curd-mill.] [Illustration: FIG. 40.--Barnard curd-mill.] [Illustration: FIG. 41.--Junker curd-mill.] [Illustration: FIG. 42.--Harris curd-mill.] There are many kinds and styles of curd-mills on the market. Gosselin, Barnard, Pohl, Junker, Victor, Harris are well-known kinds (Figs. 39-42). Some are hand, others power mills. Some of these tear the curd into pieces of unequal size, others cut it into uniform pieces. A mill that will do the work with the least possible pressure on the curd and which will cut it into small uniform-sized pieces is most desirable. The ideal mill should release the least fat and leave the curd in the best condition to receive the salt. It is impossible to run curd through any mill without exposing some fat on the freshly cut surfaces, and if the curd is put under pressure, more fat will be pressed out and lost. Cutting in the mill, like cutting the curd after coagulation by rennet, may be called a necessary evil. There is an unavoidable mechanical loss which may be greater or less according to the mill used. If the curd has been properly handled so that the water in it has become thoroughly assimilated (properly incorporated), this loss will be reduced to the minimum. If the curd contains free moisture and many of the particles have soft interiors, a stream of white whey will run down the vat as the curd masses are cut. Some samples of such white whey will test as high as 15 per cent fat. This not only causes a loss in yield but in quality of cheese, according to the amount of fat lost. White whey is an indication of loss of fat. If the proper amount of moisture is present and is so thoroughly incorporated in the curd that it can be separated only by evaporation, the ideal condition has been reached. While milling, the cut curd should be stirred as fast as milled to prevent matting again and to allow odors to escape. This stirring is usually performed with a curd fork (Fig. 43). At the same time the temperature will be lowered. The milled curd should be spread evenly over the upper