CHAPTER V 

 CONDITIONS FAVORING MOLD GROWTH 



When a piece of bread or cheese goes bad, it gets moldy ; 

 when a bottle of fruit juice spoils, the organisms growing in 

 it (as we shall learn later) are either yeasts or molds ; but 

 the spoilage of a can of vegetables, like corn or beans, is 

 almost invariably due to bacteria. Why can molds grow 

 in the first two instances but not in the third ? The answer 

 to this question is important, for it shows how to control 

 their growth. 



Food Requirements. Like nearly all other kinds of 

 microorganisms, molds require organic matter. As food is 

 always composed of organic matter, they have no trouble 

 in meeting this requirement. Were this the only peculiarity 

 of their food needs, all food would mold; but there are 

 certain other respects in which they prefer quite different 

 food from ordinary bacteria. They like a large amount of 

 sugar. Most bacteria can use sugar ; but if a fluid contains 

 as much as two per cent of sugar the growth of ordinary 

 bacteria is decidedly inhibited. Quite the contrary with 

 molds. They grow well even with larger percentages of 

 sugar. One reason for this difference is that when a micro- 

 organism grows in the presence of sugar, this substance is 

 converted into acids ; and it requires only a small amount 

 of acid to prevent the growth of the ordinary decomposition 

 bacteria. Molds, however, grow best if there is a little acid 

 present, and they tolerate a considerable amoimt of it. 



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