They are responsible for many types of spoilage in refrigerated foods, such as slime formation on meats and ropiness in milk. You can see, therefore, why it's so important to store unprocessed foods under refrigeration. These bacteria can cause spoilage in under-processed canned foods. As noted earlier, microorganisms are essential in the production of certain foods. Yeasts Yeasts are small, single-celled plants.
Fungi differ from other plants in that they have no chlorophyl.
Bacteria thrive on many different types of food. But most yeasts can live only on sugars and starches. From these, they produce carbon dioxide gas and alcohol. Thus, they have been useful to man for centuries in the production of certain foods and beverages. They are responsible for the rising of bread dough and the fermentation of wines, whiskey, brandy and beer.