WHY DO FOODS SPOIL? 



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ccrrloon. 

 dio>dde 



TorectcL 



When yeast plants grow they break down their food into carbon dioxide and 

 alcohol. How would this account for the rising of bread ? 



are called microorganisms. They include the bacteria, 

 yeasts, and molds. Bacteria multiply with very great 

 rapidity once they get a favorable place in which to live. 

 They must have dead or living foods in order to grow, 

 since, unlike green plants, they cannot make their own 

 food. Yeast and molds likewise grow rapidly when food 

 and temperature conditions become favorable. We know 

 that the action of bacteria will cause the decay of various 

 organisms. Sometimes they give up poisons as a result 

 of their growth. Some will cause milk to sour and some 

 will even cause diseases of various kinds. These tiny 

 plants, yeasts, molds, and bacteria, are always present 

 in the air although we cannot see them, and when they 

 settle upon foods and grow rapidly, they cause the foods 

 to spoil, changing both the taste and odor. 



Yeasts and Their Work. Every one knows that yeast 

 under certain conditions of warmth and moisture causes 

 bread dough to "rise," but it is not so well known that 

 this condition is caused by the growth of millions of tiny 

 one-celled plants which were in the compressed yeast cake. 

 Wild yeasts occur almost everywhere and, under favorable 

 conditions, cause the process of fermentation to take place. 

 In this process the yeast plants break down the sugar 

 and starches on which they feed into carbon dioxide 

 and alcohol. Yeast plants often get into sweet foods, 



