If you don’t bake very often, pay particular attention to the health and well-being of your leavening agents. If your baking powder or baking soda has died, your baked goods are going to fall flat through no fault of you own! In this photo, both batches of Pumpkin Pear Muffins were baked from the same recipe, only the sunken muffins on the right used "expired" baking powder.

Most tins of baking powder have a “use-by” date stamped on the bottom, but that doesn’t absolutely guarantee a fully rising agent. The Clabber Girl baking powder company Web site (click here) suggests storing baking powder in a cool, dry cabinet.

Then, before using it, “stir up the powder to see if there are any clumps, or if it has hardened.” If so, “this is an indication that moisture has mixed with the powder and caused a reaction. If it stirs up nice and fluffy, it should be good.” (Never dip a damp measuring spoon into the can as the moisture will ruin it.)

Lots of other Web sites recommend “testing” the baking powder by putting a teaspoonful into a glass of slightly warm water to see if it fizzles or bubbles. If so, it’s still potent. If it just sits there, buy a new can.

Even though I bake fairly often, I still buy the smallest container of baking power I can find. Since most recipes just call for a teaspoon or so, it’s takes practically forever for me to use up a large can.

When it comes to baking soda, also called for in many sweet breads, muffins and cakes, there is no easy test for freshness. The Arm & Hammer company prints a date on each box, but their Web site says when in doubt, buy a fresh box. (That’s useful for the company, obviously, but baking soda is extremely inexpensive as ingredients go. You’re better off using fresh rather than risk ruining your muffins.)

Finally, I’ve always wondered what’s the difference between baking powder and baking soda, and whether they are interchangeable. So I loved this clear-cut explanation from the Arm & Hammer site:

Baking Soda is pure sodium bicarbonate. Baking powder is a mixture of baking soda and various acidic ingredients. Both baking soda and baking powder help dough rise. Baking Soda will react in combination with acidic ingredients in a recipe (like cream of tartar or lemon juice) to release the carbon dioxide that causes dough to rise. Baking powder, which already contains the acidic ingredients to make the carbon dioxide producing reaction, is used in recipes without other acidic ingredients.