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By Robert L. Wolke
Wednesday, August 31, 2005

From time to time I use household bleach in the kitchen -- for example, I splash some into a plastic food container full of water to get rid of lingering odor from tuna salad. I have also used a weak bleach solution on plastic cutting boards to rid them of discoloration. Is this effective, and if so, what is a sensible ratio of bleach to water?

Household chlorine bleach is a powerful oxidizing agent. It bleaches out colors by oxidizing the colored compounds into colorless ones.

To a chemist, "oxidation" has the broad meaning of stealing electrons from a molecule. It's the electrons in a substance that make it colored by absorbing certain specific wave lengths of light. Get rid of those electrons, and you get rid of the color. That's what the bleach does.

Like you, I use chlorine bleach to remove stains from my polypropylene cutting board and from the white porcelain linings of my favorite set of French saucepans. It doesn't take much; a shot glass (1 1/2 ounces) of bleach in a quart of water is strong enough. (Observe the precautions on the bleach bottle's label.) Fill your plastic containers or porcelain- lined saucepans with the bleach solution and let them stand until the discoloration is gone. For the cutting board, spray it with a general-purpose detergent such as Formula 409, then paint the bleach solution onto it with a pastry brush and let it stand until the stains disappear. (The detergent helps the bleach solution to wet the plastic.) Then rinse the containers and cutting board thoroughly. Don't forget to rinse the shot glass and the pastry brush.

Sodium hypochlorite, the chemical name for household bleach, is alkaline and, like most alkalis, is slippery and hard to rinse off completely with water, so its chlorine smell will linger. A final rinse with white vinegar will neutralize the hypochlorite and kill the odor.

In Heloise mode, I add vinegar to the final rinse water of a chlorine-bleached load of white laundry, because I hate the smell of chlorine on my handkerchiefs.

By the way, sodium hypochlorite is an excellent disinfectant, so your cutting board should be germ-free as well as stain-free.

I always thought I knew the difference between fruits and vegetables but am no longer sure. Tomatoes, though often considered a vegetable, are actually a fruit. They are the result of a plant's reproductive process which, I understand, is what defines a fruit.

Does the same hold true for cucumbers, zucchini, pumpkins and squash? I've never heard of them referred to as fruits but aren't they also the offspring of flowering plants? And what about peas, string beans and other beans? Aren't they fruits as well? Peas, string beans and beans are referred to as legumes, I think, because of the nitrogen-fixing capability of their roots.

So, are they leguminous fruits? What about peanuts? They grow below ground like potatoes, so are they legumes (because their roots fix nitrogen) as well as vegetables, being a non-flowering part of a plant (the definition of a vegetable), i.e., root, stem, or leaf? Finally, what about tree nuts? Surely they must be fruits, right?

Plants are made up of many more complex components than simply roots, stems and leaves, depending on how exhaustively one wants to deconstruct them, even down to the cellular level. But when the main reproductive part of a flowering plant -- the ovary -- matures, it becomes a fruit, whose purpose is to protect and nourish the seeds of the next generation.

Botanically speaking, then, the seed-bearing tomato is clearly a fruit, but not necessarily in the eyes of the law. In 1893, the U.S. Supreme Court ( Nix v. Hedden ) declared that tomatoes are vegetables, not fruits. A literalist tomato importer named John Nix was therefore forced to pay duty on his tomatoes, whereas imported fruits were duty-free. (May I suggest that Supreme Court nominee John G. Roberts Jr. be asked about his position on tomatoes?)

Some other "vegetables" that are botanically legitimate fruits are the cucumber, zucchini, pumpkin and squash that you mention, as well as -- perhaps surprisingly -- grains, including corn, rice, and wheat; all tree nuts; and some spices such as chili peppers and nutmeg.

But that's botany. In gastronomy, the term "fruit" is usually reserved for those that are sweet and fleshy, such as apples, peaches, bananas and so on. In fact, the word "fruit" comes from the Latin fructus , meaning enjoyment, presumably referring to the sweetness of a ripe fruit. There are hundreds of known edible fruits, plus untold numbers of inedible ones.

Then there is the category of leguminous plants, whose seeds, called legumes, are produced in pods. Among these are peas, soybeans, lentils, peanuts and the many kinds of beans. Botanically, these are all dry (not fleshy) fruits, a fact that doesn't prevent them from having another distinguishing characteristic: Their roots enrich the soil. They provide nodules in which nitrogen-fixing bacteria reside while converting nitrogen in the air to ammonium compounds, nitrates and other chemical forms that plants can utilize.

The leguminous fruit we call peanut, by the way, doesn't fit the botanical definition of a nut. But that's another column.

Robert L. Wolke (http://www.robertwolke.com) is professor emeritus of chemistry at the University of Pittsburgh. His latest book is "What Einstein Told His Cook 2, the Sequel: Further Adventures in Kitchen Science" (W.W. Norton, 2005). He can be reached atwolke@pitt.edu.


© 2005 The Washington Post Company

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