MICROBIOLOGY OF FERMENTFD FOODS 563 



Yeast as Food. Yeast is very rich in protein and forms a readily 

 assimilable human food or stock food. Breweries and distilleries 

 produce very large quantities of yeast as a by-product. In the case of 

 breweries, the yeast carries a considerable quantity of hop resins which 

 impart a bitter taste to the product and render it unpalatable for human 

 food. It is, however, fed successfully to stock with the spent grains. 

 By suitable washing processes most of the bitter resins may be removed. 



In addition to its nutritive value it is claimed by some that yeast 

 taken internally or applied externally possesses remarkable healing 

 properties for wounds, boils, pimples, etc. It is also claimed that yeast 

 is rich in vitamins, the now popular growth-producing compounds. 

 These contentions are, however, not yet fully substantiated by thorough 

 investigations. 



Yeast may be dried successfully at moderate temperatures, but 

 tends to caramelize or darken at temperatures used for fruit drying. 

 The dried product makes an excellent protein concentrate for stock or 

 may be used satisfactorily in flavoring many dishes prepared in the 

 household and is suitable for the preparation of soups. An extract may 

 be made from yeast and concentrated to a syrupy consistency as is meat 

 extract. The product has a flavor similar to that of meat extract and 

 may be used for the same purposes. 



Large quantities of yeast have been grown by factories in Germany 

 primarily for stock food, using cheap molasses as a source of carbo- 

 hydrate for yeast growth and ammonium sulphate as a cheap source of 

 nitrogen for protein formation. The process offers a very quick method 

 of producing protein from inorganic nitrogen. A combination of a 

 bottom yeast of the Strept. cerevisia or ellipsoideus type and a rapidly 

 growing film yeast of the Mycoderma cerevisia or M. mni has given the 

 greatest yields of yeast per pound of raw material used. Dilute solu- 

 tions yield relatively larger amounts of yeast than do more concen- 

 trated solutions. 



Sugary solutions from the hydrolysis of wood may be used as a 

 source of carbohydrate instead of molasses. In fact, a variety of waste 

 products might be utilized in this manner. This method of producing 

 cheap protein possesses great possibilities and will become an im- 

 portant industry it is believed, as the world demand for food becomes 

 more acute through increase of population. 



