LABORATORY GUIDE IN BACTERIOLOGY 

 EXERCISE 7. EXAMINATION OF BREWER'S YEAST 



1. Secure some brewer's yeast. 



2. Inoculate a tube of liquid wort and incubate at 

 25 C. 



3. Prepare pure cultures from this mixture accord- 

 ing to Hansen's method. 



4. When pure cultures have been obtained, study 

 these in the same manner as previously directed. 



SECTION 4 

 EXAMINATION OF BAKER'S YEAST 



1. Prepare 5 flasks with 100 c.c. sterile water. 



2. Secure a cake of pressed yeast. 



3. Prepare a suspension of i gram in 100 c.c. 

 sterile water. 



4. Weigh out about one gram, evaporate on a water 

 bath, place in a calcium chlorid desiccator over night, 

 weigh again, and determine the percentage of moisture. 



5. Remove 10 c.c. water from a flask containing 

 loo c.c. sterile water, and replace with 10 c.c. from the 

 suspension. 



6. Transfer i c.c. of the suspension to another dilu- 

 tion flask. 



7. Transfer i c.c. from the second flask to a third 

 dilution flask. The dilutions prepared are 1:100, 

 i : 1,000, i : 10,000, 1:100,000, not considering the 

 amount cf moisture in the gram of yeast suspended. 



8. Pour meat extract agar and wort agar plates 

 from all dilutions. 



9. Incubate the meat agar plates at 37 C. and the 

 wort agar plates at 25 C. 



