ACIDS AND PICKLED FOODS

The addition of acids to foods lowers their pH and inhibits the growth of many microorganisms by affecting enzyme activities. Foods with high acid content, such as citrus fruit and tomatoes, are more resistant to spoilage than low-acid foods, such as corn and beans. Low-acid foods can be made more resistant to spoilage by storing them in acidic vinegar, a technique called pickling. Cucumbers, beets, and other vegetables are commonly preserved this way, with a bit of garlic, dill, or other spices added to enhance the flavor.

Some microorganisms ferment sugars and release acids as they grow in sugar containing foods. For example, the lactic acid bacteria ferment milk sugars and produce the lactic acid found in sour milk, some cheeses, and other "cultured" dairy foods. Vegetables such as cabbage and cucumbers, when fermented, are converted into sauerkraut and pickles, respectively, which are more resistant to spoilage than the fresh vegetables. Today fermentation is rarely used commercially to prepare products such as sauerkraut and pickles. It is more efficient simply to add acetic acid solutions to cabbage or cucumbers.