Mayonnaise, in its purest form, is a mixture of eggs and vegetable oil (typically canola, soy, or olive oil). Lemon, vinegar, and a touch of sugar are also ingredients in homemade mayo, as well as the commercial brands. The "egg" piece is critical: There was a recent lawsuit between a major mayonnaise-producing company and a smaller maker over the use of the word "mayo" for a product that did not contain eggs. The lawsuit cited the Food and Drug Administration regulation that for a product to be called mayonnaise, it must contain eggs. (The abbreviated "mayo" is another thing.)

Those eggs have created an additional mayonnaise hullabaloo. Some people believe that it's unsafe to bring dishes containing mayo to a warm-weather event because the ingredients are unstable and promote bacteria. Time was, mayonnaise was made from scratch with unpasteurized eggs. But with today's pasteurization process—plus the inclusion of acidic vinegar and lemon as well as salt—mayonnaise is stable and unlikely to cause a food-borne illness. You don't want to leave any food out for long on a sweltering day, of course—no more than one hour is what the FDA recommends. After that, keep salads in a cooler packed with ice.  —Nanette27

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This article was first published in the June/July/August 2015 issue of Allrecipes magazine.