In the old days women baked several times a week for their family and keeping fresh baking powder on hand was no problem. How many times I have been dismayed when my biscuits didn't rise. A quick check of my baking powder and sure enough, it expired 3 years ago. Now it is not the cost of replacing the baking powder it is the disappointment when my baked goods do not meet my expectations. Well I found the solution so I now always have fresh baking powder at hand.
Baking powder is cream of tartar, baking soda and corn starch. I found that cream of tartar will stay fresh as long as it does not get wet. And baking soda has a very long life as long as it is sealed against odors and moisture. Now if you want you can mix a small amount of baking powder ahead of time to have on hand or simply add the baking soda and cream of tartar as you cook. You do not need the corn starch so leave it out unless for some reason you want to add it. If you mix it ahead of time, remember it can go flat over time just like your store bought. And remember 3/4 of a teaspoon will equal 1 teaspoon of baking powder.
What is cream of tartar? Cream of tartars' chemical name is potassium bitartrate, and is a byproduct of wine making. You will find cream of tartar with the baking spices at your food store. After I open my cream of tartar I place one or two silica gel desiccants in the jar.
1/2 teaspoon cream of tartar, and 1/4 teaspoon baking soda = 1 teaspoon baking powder. If you want you can add the 1/4 teaspoon corn starch.
So there you go, a simple solution that our grandmothers knew.
Testing Your Baking Soda
Add 1/2 teaspoon baking soda to a few tablespoon of white distilled vinegar. If it’s fresh, the mixture should fizz and bubble furiously.
Testing Your Baking Powder
Add 1/2 teaspoon baking powder to a few tablespoons of warm water. The mixture should fizz moderately if the powder is fresh. No reaction, time for new.