The curd is not cheddared very long but is milled early so that the whey can escape. If it is thought that the cheese will be sour, the curd should be washed in cold water to remove the acid and milk-sugar. A little more salt is sometimes used. A product made from over-ripe milk, no matter how skillful the cheese-maker, will show traces of a sour cheese. (2) _Gassy milk._--If a cheese-maker knows that there is "gassy" fermentation, he should add more starter and develop more acid when ripening the milk to try to overcome this. There are different kinds of gassy fermentation. Some produce acid and some do not. Some will not show until the cheeses have been on the curing-room shelves several days. Others will cause the curd to float in the whey. Usually the gas shows as pin-holes while the curd is being cheddared. [Illustration: FIG. 51.--This shows the same cheeses as in Fig. 50, cut open to show the solid and gassy texture.] The gas causes tiny round holes in the cheese, resulting in the cheese swelling or puffing out of shape and sometimes breaking open (Figs. 50, 51). The only time to overcome the gas is during the cheddaring process. The curd is piled and repiled until the holes flatten out. This shows that the gas-producing organisms have weakened and will not cause any more holes. Because the curd has to be piled so many times and so long, the pieces become very thin. The curd is ready to mill when most of the holes have flattened. After milling, the curd should be stirred and aired for some time before salting to allow the bad odor to escape. Because of the high acid development, it often happens that the cheese will not be gassy but will be sour. At best a cheese made from milk having gassy fermentation will have a bad flavor. The quality of the cheese can be no better than that of the milk from which it is made, plus the skill of the cheese-maker. +209. Qualities of Cheddar cheese.+--The cheese should be neat, clean and attractive. If unclean, and the bandage not put on the cheese properly, it shows that the manufacturer is not particular to keep the curing-room shelves tidy nor careful and painstaking in dressing. The cheese should not be lopsided or bulged. When cut, it should have a uniformly colored interior. The principal color defects are too high, or too light color, mottled or seamy. The texture should be solid and close. A common defect is mechanical holes or openings and another is gas pockets. The body can be tested by rubbing the cheese between the thumb and fingers. It should be smooth and waxy and free from lumps. It should rub down like cold butter. The common defects are graininess and lumpiness. Graininess may be caused by too much acid or too much moisture in the cheese. Lumpiness is due to uneven curing. If too much moisture is present, the body will be soft and mushy; if not enough moisture, the body will be hard and dry.