YEAST SPOILAGE IN FOOD PRODUCTS 345 



comitant reduction of a second molecule) at the phosphorylated 

 triose stage as follows. 



Triose diphosphate + DPN — > diphosphoglyceric acid + H2-DPN 



Triose phosphate + H2-DPN ^ glycerophosphate + DPN 



Triose diphosphate + triose phosphate — > 



glycerophosphate + diphosphoglyceric acid 



Special strains of yeast, "trained" to grow in alkaline medium, gave 

 the highest yield of glycerol. Blackstrap molasses, corn sugar, and 

 sucrose were all found to be suitable as the carbon source when the 

 other essential nutrients were added. Soda ash, because of its low 

 cost, was recommended for use but any substance which makes the 

 mash alkaline can be used. Eoff recommended the addition of soda 

 ash in five portions during the fermentation. 



YEAST SPOILAGE IN FOOD PRODUCTS 



In foods preserved from bacterial decomposition by low pH or 

 high osmotic pressures, yeasts as well as molds may grow and cause 

 considerable economic loss. Unlike the molds, however, yeasts are 

 not at all active in the decomposition of proteins. They become 

 undesirable because of the active fermentation of carbohydrates 

 which they carry out with resultant gas production. In some cases, 

 they probably act as does Geotrichum candidum, upon organic acids, 

 raising the pH of the medium to a point where putrefactive bacteria 

 may grow. Owing to their ubiquitousness, certain asporogenous 

 yeasts (usually designated as Torula in industrial literature) and, 

 in some instances, sporulating yeasts have been found undesirable 

 contaminants in a wide variety of foodstuffs. 



Yeasts are extraordinarily abundant in various dairy products, 

 notably cream, butter, and cheeses. Yeasts occur quite regularly 

 in cream, and the numbers rise considerably when the cream sours. 

 They are naturally abundant in butter. In some cheeses, as Camem- 

 bert, yeasts make up a large proportion of the microbic flora. Lac- 

 tose-fermenting yeasts occasionally give considerable trouble in 

 cream, producing a marked gaseous fermentation known as foami- 

 ness. These organisms are constantly present in cream, and the fer- 

 mentation can be prevented by proper cooling. 



Tomato catsup, honey, sugar syrup, and fruit juices are all sus- 

 ceptible to spoilage by fermenting yeasts. The chemical composi- 



