CHAPTER XIV 
FOOD PRESERVATION 
‘Tue relation of bacteria to foods may be considered from several 
viewpoints. With regard to the changes which they induce in foods 
they may be divided into two general classes—the desirable and the 
undesirable. These may be divided somewhat after the following 
manner: 
I. Desirable microorganisms: 
A. Bacteria 
(a) Fermented milks 
(6) Cheese and butter 
(c) Pickles, sauerkraut, etc. 
(d) Ensilage 
(e) Industries, leather, retting, ete. 
B. Yeasts 
(a) Leavening agents 
(b) Wine and beer 
C. Molds 
(c) Cheese 
II. Undesirable Microorganisms: 
A. Those which cause spoilage 
(a) Fermentation, putrefaction 
B. Those which cause food poisoning 
The question of food spoilage may be discussed from a number of 
viewpoints. Some have taken up each special food such as milk, meat, 
etc., and discussed the types of change, organisms, etc., which are 
involved. More recently, however, Rahn (1913) has pointed out the 
possibility of discussing the large groups of food substances which 
undergo decomposition and not mentioning each particular food. For 
this purpose, he has devised the following groups, which serve very well 
as a basis for a consideration of food spoilage: 
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