56 GARDEN PROJECT 
called fermentation. Preserves containing a high per- 
centage of sugar do not ferment. 
Bacteria a serious menace. Bacteria are more seri- 
ous enemies than yeasts or molds. As has been men- 
tioned, they are the friend of the farmer as well.as of 
the dairyman. To them is due the flavor of butter and 
cheese. The housewife, however, must wage a con- 
tinuous battle with them in preserving food stuffs. 
One of the most wonderful things about bacteria is 
their power of reproduction. It is estimated that they 
reproduce themselves every half hour. At this rate, a 
single bacterium would result in the production of 
17,000,000 in twelve tours. Most plants reproduce by 
means of seeds but bacteria reproduce by means of. 
spores. All bacteria are killed by prolonged heating, 
although some species produce spores which are re- 
sistant to almost all temperatures. 
Bacteria will not grow at freezing temperature or 
below nor usually at a boiling temperature though 
some species grow at 140° F. Most bacteria grow best 
between 70° F. and 90° F. The exact temperature at 
which they are killed varies with the species. What 
makes the bacteria difficult to kill is the fact that there 
are two forms, the spore form and the vegetable form. 
The spore form will often resist a temperature as high 
as boiling water. Only higher temperatures or pro-... 
longed boiling will kill some spores. 
Bacteria require darkness, moisture (25-30%) and 
heat for best growth. Molds will grow upon acid sub- 
stances but bacteria will not. This explains why fruit 
preserves are not attacked by bacteria. Like animals, 
bacteria require food containing sugars, starches, and 
protein. 
What are ptomaines? Bacteria not only destroy 
