Knowledge of some of the basic facts about food perishability can help one avoid food poisoning on picnics, Indiana Medicine (79:360) reports. Because the bacteria that cause food poisoning cannot flourish or even survive for long in acid surroundings, special precautions are necessary with foods that are low in acid, such as chicken, ham, eggs, and potatoes, all of which are common ingredients for sandwiches and summer meals outdoors. As most readers already know, these foods should be taken out of the refrigerator at the last moment and kept in an insulated cooler next to a frozen ice can.

It is not so well known, however, that mayonnaise and salad dressing, by virtue of their lemon juice and vinegar ingredients, are strongly acidic and therefore help prevent the growth of bacteria that cause food poisoning. Thus, the sooner that mayonnaise or salad dressing can be added to non-acid foods and salad materials after they are taken from the refrigerator, the lesser is the chance that food will be spoiled by dangerous bacteria.

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