Baking Soda and
Baking soda is bicarbonate of soda and is a prime ingredient of baking powder. It is akaline in nature, and when combined with an acid, it creates carbon dioxide bubbles, giving rise to doughs and batters. Since it reacts with water, it should be mixed thoroughly with dry ingredients before adding liquids to insure even leavening. Baking soda alone is normally used when sour milk, buttermilk or other acidic liquid is used in the recipe.
Although baking soda was once added to water when boiling green vegetables to preserve color, it's now known that this process destroys vitamin C content, so eschew that old wives' tale.
Baking powder is basically a blend of acid (most commonly calcium acid phosphate, sodium aluminum sulfate or cream of tartar) and alkali (sodium bicarbonate known commonly as baking soda). By adding water to this mixture, a chemical reaction is achieved, producing carbon dioxide which is trapped in tiny air pockets in the dough or batter. Heat releases additional carbon monoxide and expands the trapped carbon dioxide gas and air to create steam. The pressure expands the trapped air pockets, thus expanding the overall food.
There are three kinds of baking powder:
• Double-acting: Releases leavening gases on contact with moisture and again during baking.
• Tartrate: A single-acting powder that releases a volume of gas the instant it touches moisture.
• Phosphate: A slightly slower-to-react single-acting powder.
The most commonly used baking powder is the double-acting, which can be readily found in any grocery store. The other two are becoming increasingly difficult to find. Be sure to read labels carefully to determine which type you are working with. Those who have older recipes calling for tartrate or phosphate baking powders will probably have to go to an imported foods purveyor or order from abroad.
Baking powder does lose its potency over time. Thus, you should always "proof" your baking powder before using it in a recipe by pouring 1/3 cup of hot tap water over 1/2 teaspoon of baking powder in a cup. The mixture should bubble enthusiastically. If it doesn't, toss it out. Be sure to thoroughly mix baking powder with other dry ingredients before adding any liquid. Commercial baking powders have about a one-year shelf life, if stored sealed in a cool, dry place.
If you find yourself without baking powder, you can make your own in a pinch. For one teaspoon of baking powder, mix 1/2 teaspoon of cream of tartar with 1/4 teaspoon baking soda. If you plan to mix your own to store, also add 1/4 teaspoon of cornstarch to that ratio, as the cornstarch will absorb any excess moisture in the storage container and avoid a potential premature reaction. Also keep in mind that homemade baking powder works faster and at a lower temperature, so put your recipe together quickly.
And here is another recipe to try as well.
1/4 cup bicarbonate of soda
1/2 cup cream of tartar
1/2 cup arrowroot starch
Combine these ingredients thoroughly and store in jar. Makes 1 1/4 cups of baking powder. The arrowroot repels moisture, so it keeps well. To make baking powder for immediate use, combine 1/4 teaspoon cream of tartar with 1/4 teaspoon bicarbonate of soda. This is the equivalent of 1 teaspoon of commercial baking powder and has 225 milligrams of sodium. To make sodium-free baking powder, eliminate the sodium bicarbonate and substitute potassium bicarbonate which is available at pharmacies.
You must also take care in substituting buttermilk for regular milk when using baking powder, as it upsets the balance of alkali to acid. Buttermilk has more acid than regular milk, which will reduce the carbon dioxide released and thwart the leavening process. To achieve the desired result when using buttermilk instead of milk, substitute baking soda for some or all for of the baking powder. For each cup of buttermilk used in place of sweet milk, reduce the amount of baking powder by two teaspoons, and replace with 1/2 teaspoon of baking soda.
High altitudes will also affect the amount of baking powder needed in a recipe. Atmospheric pressure affects the reaction of carbon dioxide. Air pressure is lower at higher altitudes, the carbon dioxide expands more; and thus, less baking powder is needed. If you do not cut back, the texture will be rougher. This may take a little experimention for your own particular high altitude.