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 V.13 No.9 | February 26 - March 3, 2004 

Food 101

What Makes Food Go Bad?

The better question may be: What keeps food from going bad?

Q: I've always wondered why some foods go bad so quickly even if refrigerated, while others seem to last forever without refrigeration. Is there any rule of thumb?

A: If life were that simple were that simple! There can be no single rule that covers all the foods we consume—an almost infinite number of combinations of thousands of different proteins, carbohydrates, fats and minerals that make up our omnivorous diet. "Going bad" can refer to the effects of bacteria, molds and yeasts; of heat; of oxidation from exposure to air; or of enzymes in the foods themselves.

Not to spoil your appetite, but all foods will eventually spoil, rot, decompose, disintegrate, crumble, putrefy or turn rancid. The proteins will turn soft, squishy, putrid and green; the carbohydrates will ferment; the fats will turn rancid and sour.

Refrigeration will slow down all of these processes, but there are limits. At a typical home refrigerator temperature of 40° F, for example, 10,000 bacteria can grow to 10 billion in four days.

Enter, preservatives: chemicals that are added to prepared foods to extend their lives—and ours. Yes, they are chemicals. And yes, they are additives, because, obviously, they have been added. (So have salt, sugar, spices, vitamins and so on.) Quite simply, without preservatives most of our foods would spoil.

And yet we are continually wooed by food labels demurely hinting at their superiority with the phrase, "Contains no additives or preservatives." (Some day, I'd like to see a label that adds, "Will spoil the minute you get it home.")

What are these chemicals? They fall mostly into four categories.

Antimicrobials inhibit the growth of bacteria, molds and yeasts. They include sulfur dioxide and sulfites (used in fruits, fruit juices, vinegars and wines), sorbic acid (used in cheeses), calcium propionate and other propionates (used to inhibit molds in bread and other baked goods), and sodium and other benzoates (used to prevent fungal growth in beverages, fruit preserves, cheeses, pickles and many other products).

Antioxidants inhibit oxidation by air, which makes fats, especially unsaturated fats, turn rancid. They include sulfites, BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene), TBQH (tertiary butylated hydroquinone), ascorbic acid(Vitamin C) and propyl gallate. You'll find them in potato chips, nuts, cereals and crackers.

Enzyme inhibitors slow enzyme-driven spoilage reactions in foods. Sulfites inhibit the enzymatic degradation reactions in fruits such as raisins and dried apricots.

Sequestrants, also known as chelating agents, gobble up atoms of trace metals such as iron and copper, which catalyze (accelerate) oxidation reactions and cause discoloration. The most used chelating agent is EDTA (ethylenediamine tetraacetic acid). Other sequestrants are polyphosphates and citric acid.

OK, so some of these chemical names are unpronounceable, which, contrary to some opinions, doesn't make them evil. They're all present in tiny amounts regulated by the Food and Drug Administration, and nobody eats them by the spoonful.

The alternative is to visit the farm or farmers market every week and make your own cream, preserves, pickles, cheese, wine, potato chips, cereals and olive oil, being sure to consume them before they go bad. Welcome to the 18th century!

Robert L. Wolke (www.professorscience.com) is professor emeritus of chemistry at the University of Pittsburgh and the author of What Einstein Told His Cook: Kitchen Science Explained.

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