Chilling Thoughts

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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.


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© 2005 The Washington Post Company

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