+78. Cheese color.+--An alkaline solution of annatto is usually used as a cheese color. This colors both casein and fat in contrast to butter color which is an oil solution of the dye and mixes only with the fat. Cheese color is added to the milk in making some varieties of cheese, and not for others. When lactic starter is used, the color should be added after the starter and just before the addition of the rennet. The amount is determined by the color desired in the cheese. The usual amount varies from one to four ounces to each thousand pounds of milk. Before adding, the color should be diluted in either milk or water, preferably water. It should then be mixed thoroughly with the milk. +79. The acidity factor.+--Milk as drawn shows a measurable acidity when titrated to phenolphthalein with normal sodium hydroxide. This figure varies with the composition of milk. Casein itself gives a weakly acid reaction with this indicator. Calculated as lactic acid, this initial acidity varies within fairly wide limits, records being found from 0.12 to 0.21 of one per cent or even more widely apart. Commonly, however, such titration shows 0.14 to 0.17 per cent. Some forms of cheese (Limburger, Swiss, Brie) are made from absolutely fresh milk. Acidity from bacterial activity is important as a factor in the making of most types of cheese and probably in the ripening of all types. Increasing the acidity of the milk hastens rennet action and within limits produces increased firmness of the curd. If carried too high, acidity causes a grainy or sandy curd. Normally fresh milk is sufficiently acid in reaction when tested to phenolphthalein to permit rennet to act, but the rate of action increases rapidly with the development of acid. Increase of acidity may be accomplished: (_a_) by the addition of acid as has been done by Sammis[25] and Bruhn in pasteurized milk for Cheddar cheese; or (_b_) by the development of acid through the activity of lactic organisms, which is the usual way. For renneting, the acidity necessary for particular cheeses runs from that of absolutely fresh milk still warm (as in French Brie, Limburger, Swiss, Gorgonzola) through series calling for increase of acidity, hundredth by hundredth per cent calculated as lactic acid. This ranges from 0.17 to 0.20 per cent as is variously used in American factory Cheddar to about 0.25 to 0.28 per cent as obtained by adding acid in Sammis' method. This method is discussed under the heading "Cheddar Cheese from Pasteurized Milk" (p. 229) since it requires special apparatus and has not thus far been used with other types of cheese. For the development of acidity by the action of bacteria, lactic starter is almost universally used. This may be added in very small quantities and the acidity secured by closely watching its development or by adding starter in amount sufficient to obtain the required acidity at once. In either case, the cheese-maker needs to know the rate of action of the