CHAPTER XVI 



THE FERMENTATIONS OCCURRING IN FOOD 

 PRODUCTS 



In the preparation and handling of foods, they inevitably 

 become seeded with a great variety of organisms. This 

 contamination is a more or less constant factor, in that 

 representatives of the three great groups of microorgan- 

 isms, the bacteria, yeasts, and molds, are always introduced. 

 The relation between the groups will vary, depending on 

 the nature of the food material. Whether one group or 

 another is to be most active in the decomposition changes 

 will depend on the composition and concentration of the 

 material. Such foods as meats, which are high in protein 

 and low in carbohydrates, undergo putrefactive changes, 

 due to bacteria that act primarily on the protein. If the 

 material contains a large amount of sugar in proportion 

 to the protein, and the reaction is not acid, the type of 

 fermentation will be similar to that noted in milk in which 

 the sugar is fermented with the production of acid, and 

 the protein is not attacked to any degree. If the material 

 contains sugar and has an acid reaction, a condition found 

 in many fruit juices, yeasts are likely to be the dominant 

 type of organism concerned in its decomposition. Alcohol 

 and carbon-dioxide are the chief products of yeast action. 



The acid fermentation of milk. The souring of milk 

 is so common that it is looked upon as a normal change ; in 

 fact, its absence is more likely to be regarded as an abnor- 

 mal condition than is its occurrence. If milk could be 

 secured without microorganisms, it would remain un- 



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