The science and practice of cheese-making : a treatise on the manufacture of American Cheddar cheese and other varieties : intended as a text-book for the use of dairy teachers and students in classroom and workroom ... . with cheese-making: (i)Lactic acid bacteria, (2) gas-producing bacteria, (3)digesting bacteria, (4) bacteria producing undesir-able flavors, (5) yeasts, (6) milk-enzyms, (7) rennet-enzyms, and (8) pepsin. The ferments that are 292 SCIENCE AND PRACTICE OF CHEESE-MAKING responsible for many of the defects found in Amer-ican cheddar cheese will be discussed only briefly here,bec
The science and practice of cheese-making : a treatise on the manufacture of American Cheddar cheese and other varieties : intended as a text-book for the use of dairy teachers and students in classroom and workroom ... . with cheese-making: (i)Lactic acid bacteria, (2) gas-producing bacteria, (3)digesting bacteria, (4) bacteria producing undesir-able flavors, (5) yeasts, (6) milk-enzyms, (7) rennet-enzyms, and (8) pepsin. The ferments that are 292 SCIENCE AND PRACTICE OF CHEESE-MAKING responsible for many of the defects found in Amer-ican cheddar cheese will be discussed only briefly here,because their relations to cheese-making are fullytreated from a practical standpoint in Part II, LACTIC ACID FERMENTATION The ordinary souring of milk is due to the forma-tion of lactic acid, which is produced by the actionof lactic acid bacteria (Bacillus lactici acidi. Fig. 44)upon the sugar in milk. A large number of different kinds or types of bacteriaare able to produce lacticacid from interesting workhas been done recently(Bull. No. 42, Coll. Exp. Sta.)which shows that othermicro-organisms are oftenassociated with the micro-organisms of lactic fermen-tation and that these. FIG. 44—TYPICAL LACTIC-ACID BACTERIA (Rogers) micro-organisms associate often have the power of furnishing products thatexert a decided influence upon the rapidity of thegrowth of the lactic micro-organisms. We have already (p. 150) called attention tothe fact that the sour taste of milk is not due to thepresence of uncombined lactic acid, since little or nofree lactic acid is present in sour milk until it hasquite a high degree of acidity; but is due to acid phos-phate of calcium, which is formed by the action oflactic acid upon the insoluble -calcium compounds in MICRO-ORGANISMS AND ENZYMS 293 the milk. Milk begins to taste sour when its acidityamounts to about per cent; which really meanswhen a little over per cent of lactic acid has beenformed from milk-
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