Attention, parents: It's time to start stressing over the school science fair. Sure, it's the child's responsibility, but I'll bet even Thomas Edison would need a nudge to display his experiments neatly on a poster board.
Our kitchen became a temporary lab last week when two of my children decided to do food-related science projects.
My son chose "Which Is a Better Snack, Fruit or Junk Food?" hoping to test his hypothesis by eating as much junk food as possible to see what would happen. But when I suggested drawing some of his blood to analyze for sugar, he decided just comparing the nutritional labeling would suffice.
My daughter explored how yeast and baking powder make baked goods rise. And since she borrowed my kitchen for her baking, I'm borrowing her information for my column.
Now that "homemade" cakes and bread are often a matter pouring a box of mix into a mixing bowl or bread machine, it's time for a refresher course on what makes them magically poof up in the oven.
Yeast and baking powder are two different kinds of leavening agents.
YEAST is a living, single-cell organism that, as it grows, converts its food (through a process known as fermentation) into alcohol and carbon dioxide. The carbon dioxide gases bubble up in the dough, making it rise. To multiply and grow, yeast needs moisture, food (sugar or starch) and a warm temperature.
The Egyptians used yeast for leavening thousands of years ago. The most popular yeast today is "active dry yeast," tiny, dehydrated granules that come from the store in envelopes or jars. When mixed with a warm liquid, the cells start growing.
If left in too hot a temperature or past the expiration date, yeast dies, and your bread will be as tough as tire tread. Before using it, you can "proof" it to make sure it's still alive. Dissolve it in a little warm water and add a pinch of sugar. Set the mixture aside in a warm place for 5 minutes. The mixture should begin to foam and swell.
Yeast takes longer to rise than baking powder; that's why breads using baking powder are called "quick" breads. Yeast starters, sometimes known as "friendship" starters, can be handed down from friends and family and kept alive for years.
The famous San Francisco sourdough uses a yeast that multiplies at a lower rate than standard baker's yeast, making the bread more compact and dense. It also incorporates a type of indigenous San Francisco bacteria. The byproduct of the bacteria is what gives the bread the characteristic sourdough flavor.
BAKING POWDER is a mixture of bicarbonate of soda (baking soda) and an acid, such as cream of tartar. (Cream of tartar is a white powder made from an acid deposited on the inside of wine barrels.) The soda is an alkali, and when combined with an acid and water there's a chemical reaction. The carbon dioxide given off is trapped in tiny air pockets in the batter. When the batter is baked in the oven, heat expands the trapped carbon dioxide gas and air, and the batter rises even more.
Most baking powder in the United States is called "double-acting" because it causes the batter to rise when moisture is added and again when heated. Single-acting powders release gas only when they touch moisture during mixing.
James A. Church began marketing baking soda under the Arm & Hammer name in 1867. In 1889, William M. Wright developed double-acting baking powder under the label Calumet. Herman Hulman of Indiana began working on a formula for baking powder in 1879. Over the years, it was improved and sold under the name, "Clabber Girl."
Cake recipes using buttermilk usually call for baking soda and not baking powder. That's because buttermilk has more acid than regular milk and can cause the chemical reaction without another acid involved.
Baking powder loses potency over a couple years' time. You can test it by pouring hot tap water over a little baking powder in a cup. The mixture should bubble up. If your recipe calls for 1 teaspoon of baking powder and you don't have any, you can use 1/2 teaspoon of cream of tartar and 1/4 teaspoon of baking soda.
E-MAIL: vphillips@desnews.com