Dry days, cool nights make fall splendor

Bright underlying colors emerge in leaves when trees stop producing chlorophyll in the fall. (Christopher Baker)

People often ask what causes leaves to turn red and yellow in autumn. Actually, the colors are always there. They're just masked by the green chlorophyll in leaves, which is busy making food by photosynthesis while the sun shines.

Come autumn, shorter days and cooler temperatures cause trees to switch into energy-storage mode, at which point their leaves stop producing chlorophyll. For the few weeks before the leaves fall to the ground, they are colored only by their natural pigments. It's these colors - red and purple anthocyanins, yellow and orange carotenoids - that make fall foliage in four-season climates so glorious.

Of course, some years the show is more dramatic than others. The best conditions for intense leaf color are dry, sunny days followed by cool (but not freezing) nights. A warm, wet autumn will almost surely result in less-than-spectacular foliage because the chlorophyll loss will be less consistent. Freezing temperatures can cause leaves to drop suddenly, without showing their colorful dormancy.

Finally, trees that are under stress - whether because of pests, disease, injury, or drought - may drop their leaves with no color change at all.

How can I ensure my fireplace will be safe?

Fireplace mishaps damage more than 10,000 homes each year in the United States. To help prevent such an accident from occurring, have your fireplace inspected at least once a year, as recommended by the National Fire Prevention Association.

Your fireplace may need to be cleaned. A certified chimney-service professional (a "chimney sweep") will clear out animal nests and other obstructions, as well as creosote, a combustible substance that builds up inside a fireplace over time. The chimney sweep will also examine the firebox and flue for cracks, which may let carbon monoxide seep into the house.

These services will cost a few hundred dollars (more if extensive cleaning and repairs are required). To find a chimney sweep in your area, contact the Chimney Safety Institute of America at csia.org.

Once your fireplace is in working order, burn only seasoned wood, and use a sturdy screen to prevent embers from flying into the room. Never burn treated paper, including gift wrap, as it can release harmful fumes indoors.

How do you keep just-cut bananas from turning brown?

Many fruits and vegetables turn brown when exposed to air. Bananas are especially prone to this phenomenon, in which enzymes contained in the exposed cells of the fruit react with oxygen.

Ripeness plays a role in how quickly fruit will brown. Just-ripe bananas are slower to discolor when cut and have a firmer consistency, making them more suited to fruit salads. The sweet, intense flavor of a fully ripened banana lends itself to breads, muffins, and other cooked dishes in which a little browning isn't an issue.

There are several ways to decelerate browning. For recipes that call for raw bananas, brush slices with lemon or lime juice, or soak them briefly in water with one of these juices squeezed in. The citric acid will lower the pH of the bananas and slow the discoloration.

If you don't want your raw bananas to have the tart flavor of citrus, reduce the time the fruit is exposed to air. The best method is to cover cut bananas immediately with plastic wrap. Other ingredients in a recipe - a layer of whipped cream on a banana cream pie, a layer of cake in a trifle - can also do the trick.

Heat also deactivates the enzymes that cause browning. When baking, add the fruit at the last possible moment, and hurry the dessert into a preheated oven.

Lastly, if your bananas are ripening too quickly, store them in the refrigerator.

Adapted from Martha Stewart Living Magazine. Questions should be addressed to Ask Martha, care of Letters Department, Martha Stewart Living, 11 W. 42nd Street, New York, N.Y., 10036. Questions may also be sent by electronic mail to: mslletters @marthastewart.com. Please include your name, address, and daytime telephone number. Questions of general interest will be answered in this column; For more information on the topics covered in the Ask Martha column, visit marthastewart.com.