The Farm Table. 68 i 



This process of growth continues as long as there is abundant food 

 and oxygen, and the temperature is favorable. Reducing the temperature 

 to near the freezing point, or raising it to near the boiling point, will 

 stop the growth of the plant. In the processes of growth the yeast 

 causes fermentation, and changes part of the sugar into carbonic acid 

 gas and alcohol. Yeasts will grow in thin or thick mixtures of flour 

 and water, or flour and other liquid. They will grow in all kinds of 

 fruit juice, in light syrups, in fruits prepared with small quantities of 

 sugar, in molasses, maple syrup, etc. Yeasts will not grow in syrups 

 made very rich with sugar, or in fruits made rich with sugar, as when 

 preserved " pound for pound." They will not grow without moisture. 



Molds and Bacteria. 



Mold spores are very light, always floating in the air, and liable to 

 be on fruit and utensils. If one of these spores falls on a warm, moist 

 food, it will germinate, send fine, thread-like filaments over and into 

 the food, and the substance is soon covered with the mold. In canning, 

 preserving and jelly-making it is necessary that the food should be pro- 

 tected from mold spores. The spores are killed if exposed for ten or 

 fifteen minutes to a temperature ranging from 150° to 212°, especially 

 when moist. 



Bacteria grow in all kinds of food, but multiply most rapidly in 

 nitrogenous foods, such as milk, meat, fish, soups, beans, peas, etc. By 

 their growth in a food, some cause fermentation and some putrefaction. 

 They do not flourish in acids, or in fruits to which a great deal of sugar 

 has been added. Therefore, canned and preserved fruits are not so 

 liable to be injured by bacteria as by yeasts and molds. Most kinds of 

 bacteria are destroyed by an exposure of ten or fifteen minutes to a 

 temperature of 212 degrees. Spores must be 

 exposed to this temperature for an hour or 

 more. 



Spores answer the purpose of dried seeds 



to yeasts, molds and certain bacteria. They, Fig. 181. — A convenient pan 



,., ^1 , . 1 , r 1 i 1 „<- for use -in canning. 



like the dried seeds of any plant, have greater ^ 



power or resisting heat and cold than do the plants themselves, and 

 will stand without injury a temperature that would kill the plants. The 

 spores of some bacteria have a very great power of resistance, and they 

 are destroyed only after being exposed for two hours or more to a tem- 

 perature of 212°. It is for this reason that foods, such as meats, peas, 

 beans, corn, etc., in which bacteria grow freely, are so difficult to can. 

 If one could be sure that there were no spores in these foods, the time 

 of cooking could be very much shorter and the food would be very 

 much better. It sometimes happens that in canning fruit or vegetables 



