232 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX 
best for brewing. The yeast is cultivated in large quantity and 
then put up in a convenient form for distribution, sometimes dried, 
in which condition it will keep alive for weeks, and sometimes 
compressed into a moist cake, compressed yeast, in which condition 
it will keep only a few days. 
Bacterial Impurities in Bread-raising—The yeast cakes are 
never pure yeast, but may contain undesired bacteria, which then 
get into the dough and sometimes produce trouble. Occasion- 
ally, too, such bacteria may get into the dough from other sources 
than yeast, such as dirty water or dirty utensils in the kitchen. 
During the raising, lactic acid bacteria always grow, and they 
seem to be necessary in order to prevent the growth 
of other species of more troublesome organisms. 
i “an Sometimes such bacteria grow too vigorously and 
(: may cause trouble. At least two different faults 
Fig 46—The i bread-making are known to be caused by un- 
bacteriathatcause due growth of bacteria. The first of these is sour 
shmy bread. bread, due to the growth in the dough of acid- 
forming bacteria. This occurs most commonly when the 
laising is allowed to continue too long or at too high a 
temperature. ‘The bacteria in question will not produce trouble 
if fresh yeast be used and the raising be completed in less than 
eight hours’ time. A second fault, due to bacteria, is slimy bread. 
This is of rare occurrence, though sometimes it will infect a bakery 
and continue day after day. This bread, when fresh, appears 
normal; but after a few hours it becomes slimy, so that, when 
broken, it appears as if filled with cobwebs. The trouble is due to 
bacteria, the source of which may be either the utensils, the flour, 
or the yeast (Fig. 46). The remedy is in cleaning and sterilizing 
all baking dishes. If this does not remove the trouble it is well to 
change the brand of flour or get a fresh supply of yeast. The 
trouble may also be relieved by keeping the bread cold so as to 
prevent bacterial growth. The addition of a little lactic acid to 
the dough, or the use of equal parts of sour whey and water in 
