EXAMINATION OF YEASTS 221 
carries a fermentation valve. Add 
50 c.c. of distilled water and 1 gm. 
of the yeast to be tested and incu- 
bate at 30° C. 
Different types of valves are 
available. Alwood (1908) used a 
convenient type for studying the 
fermenting capacity of pure strains 
of yeasts. The valves are so con- 
structed that the activities of the 
yeast may be observed and the gases 
from the fermentation may escape. 
The moisture is retained by some 
absorbent such as calcium chloride 
or sulphuric acid. The apparatus 
should be weighed before and after 
the run. The Alwood valve is 
shown in Figs. 54 and 55. 
Determination of the Ferment- 
ing Power of Yeasts, Kusserow’s 
Method. Put 400 c.c. of 10 per cent 
saccharose solution and 10 gms. of 
the yeast under examination into the 
fermentation flask of the Kusserow 
08cm, 
e224 em 
©, em, 
cS “*o.8 em. 
ee 
14 cm, 
4 cms 
f 
<< -—-2.9 ems——> 
Fig. 55.—Detail of Ventilation Tubs 
for Culture Flask. (Alwood, 1908.) 
apparatus. Warm the flask and solution to 30° C. before starting. 
After the apparatus has stood for an hour at 30° C. it is connected and 
Fie. 56.—Types of 
Ventilation Valves 
which may be Used 
with Erlenmeyer 
Flasks for Testing 
the Fermenting 
Power of Fungi. 
the amount of gas formed in the next half hour is 
measured; it should be 250 c.c. The amount of gas 
for the first and second half hours is usually about 
50 and 150 c.c., respectively. Five gms. of yeast 
in 400 e.c. of 10 per cent saccharose solution in a 
flask fitted with a fermentation valve will cause a 
loss of about 6.5 gms. of carbon dioxide in twenty- 
four hours if distilled water is used; with tap water 
the loss should approximate 8 to 12 gms. 
Determination of Mycoderma in Bread Yeast. 
Press the yeast with a sterile spatula into the bot- 
tom of a small Petri dish and incubate at 37° C. 
for two days. If the yeast contains a mycoderma, 
pure white characteristic colonies will appear on 
the yellowish background of the bread yeast. 
