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Chilling Thoughts

By Robert L. Wolke
Wednesday, July 20, 2005

Why is it that people say it ruins a tomato to put it in the refrigerator? How can this be?

It does sound strange, but there is some truth to it.

Some food sources warn that one should "NEVER, NEVER" refrigerate tomatoes because that will "kill the flavor." Others say that one of tomatoes' major flavor chemicals, (Z)-3-hexenal, "disappears" upon refrigeration. These warnings are oversimplified generalizations (or over-generalized simplifications; choose one).

It's true that (Z)-3-hexenal is the strongest fragrance among the 400 or so compounds that have been found in tomatoes' aroma. It imparts a grassy or "green" note to the fruit and is actually responsible for the odor of freshly cut grass. But it isn't destroyed by low temperatures. That would indeed be counterintuitive, which is why the refrigeration story sounds suspicious. Heat can decompose chemical compounds, but cold has never been accused of doing so.

Tomatoes can suffer what agronomists call "chilling injury" if held at temperatures below about 50 degrees. (The typical home refrigerator temperature is 40 degrees.) The nature and extent of the injury -- which mostly involves changes in the tomato's texture rather than its flavor -- depends not only on the temperature and duration of chilling but also on the fruit's ripeness. That's why no simple generalization can be made about the effect of refrigeration on tomatoes.

If a tomato is not fully ripened, refrigeration will stop the ripening process and prevent the development of its full flavor and color. That's the case with those offensive balls of tasteless plastic foisted upon us out-of-season by most supermarkets. Refrigerating them would certainly be adding injury to insult.

But red tomatoes -- fully ripened on the vine and fresh from the back yard or farm market -- are less subject to chilling injury and may therefore be kept in the refrigerator for a few days without any noticeable deterioration in flavor. Much longer than that, however, and their texture could become mealy.

So if you like tomatoes ripe and cold, as I do, the tomato police won't arrest you for putting them in the fridge.

And remember that the main flavor chemicals are volatile, so don't slice your tomatoes (refrigerated or not) until just before serving them. I like to nap thick slices with a paste made of garlic cloves, coarse salt, cracked black pepper, olive oil, oregano and lime juice, all processed with a mortar and pestle.

I read in the newspaper that blueberries should be placed in freezer bags, unwashed, to be frozen for future use. The writer quoted a blueberry farmer as saying that washing before freezing toughens the berries. Is this true?

I can't imagine any basis for that statement.

There are three reasons for not washing blueberries before freezing: Completely dry berries will stay separate, instead of clumping together in ice balls; washing can remove their natural protective coating, as I wrote in my column of July 6; and moisture can encourage mold.

But as far as I can see, water cannot bring about toughness.

I feel that extra-large eggs are now barely big enough to qualify as large, and large eggs are barely big enough to qualify as small eggs. Are there any standards for eggs, and is it true that eggs are getting smaller?

Eggs come in many sizes, depending on the hen's age, breed and weight, and any stressful environmental factors such as heat, overcrowding and poor nutrition. I'm told that keeping one's chickens happy can pay off for the farmer in bigger eggs, which will sell at a higher price.

The U.S. Department of Agriculture places eggs in six categories, based on the net weight of an entire dozen. That's weight, not size. The designations and their minimum by-the-dozen weights are jumbo (30 ounces), extra large (27 ounces), large (24 ounces), medium (21 ounces), small (18 ounces) and peewee (15 ounces).

I have no evidence that hens are being raised today under more stressful conditions than in the halcyon days of small, local farms (although I'd be willing to believe that) or that the hens have therefore been laying smaller eggs. Even if that were true, the USDA's weight standards should control how they are labeled at the market. And while you're unlikely to discover a peewee stowaway in a carton of jumbos, remember that the eggs in a given dozen can vary somewhat in size, as long as they average out to the USDA's minimum weights.

Still suspicious? Weigh your eggs. If a carton of 12 large eggs weighs less than 24 ounces (don't forget to account for the weight of the carton), you're not getting what you paid for.

I spot-checked three brands of large eggs in my local market. Two cartons were labeled "net weight 24 ounces," and the eggs actually weighed 25.5 and 25 ounces. The third dozen, with no net weight statement on the carton, weighed 22.25 ounces, 7 percent less than required by law. Ironically, that carton was the only one to bear the USDA's official shield (USDA grading is optional with producers) and cost almost three times as much as the cheapest of the three.

So you may be right to question your egg sizes. Caveat emptor!

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.

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