So I was making my sister's recipe for honey oatmeal muffins today. (Aside: You should read my sister's blog. She has the Midas touch with food - all of her recipes are always fantastic.) I neglected one very important ingredient: the baking powder.

Baking powder, you see, is what leavens quick breads such as muffins. It is a combination of several acidic salts, a base (usually baking soda), and some starch to keep things dry. When it hits water, it starts reacting, and it gives off lots of little bubbles of CO2. (If you want to have some fun in the name of science, try dumping some baking soda in some vinegar - you'll see what I mean.) These little bubbles give muffins and other quick breads their light, fluffy texture. If you don't add baking powder, here's what you get:

Muffins with no baking powder

You see, when a muffin and a hockey puck love each other very very much… (Note the interesting divot effect on the bottom of the muffins.)

The picture does not do justice to the texture of the inside of the muffin. When they first came out of the oven, the inside was somewhat like a flan, only bouncier. I dug several of them out of the garbage can for this picture, and you'd be surprised how difficult it was to tear the one in half - over the intervening hours, they had hardened and become even more rubbery.

Lesson learned: Don't forget the baking powder.