Cream of tartar is a byproduct of the fermentation process used to turn grapes into wine, and it is not recommended that you try making it yourself. If you need cream of tartar for a recipe and you happen to be fresh out, there are some simple substitutions using common ingredients. The substitutions vary depending on whether you need the cream of tartar for making baked goods or for making a meringue out of egg whites.
Calculate how much baking powder you need for your recipe. If your recipe calls for cream of tartar, it's usually accompanied with baking soda. Substitute both ingredients with baking powder. For example, 1 tsp of baking powder is equivalent to the combination of 1/4 tsp of baking soda and 5/8 tsp of cream of tartar. If your recipe does not use this exact ratio, try to get the amounts as close as you can.
Measure the baking powder with an appropriately sized measuring spoon.
Mix the baking powder into your ingredients as directed by the recipe you are using. Most baking recipes instruct you to mix the dry ingredients separately.
Calculate how much lemon juice or vinegar you need as a substitution for cream of tartar. You need twice as much lemon juice or vinegar as you would cream of tartar. For example, most meringue recipes require about 1/8 tsp of cream of tartar per egg white, so you need 1/4 tsp of lemon juice or vinegar.
Measure out the necessary amount of lemon juice or vinegar. If using lemons, squeeze them into a separate container and strain out any pulp and seeds before measuring.
Add the lemon juice or vinegar to the egg whites when you are directed to add the cream of tartar. Proceed with the recipe as you normally would.
Most recipes that call for cream of tartar call very small amounts, so any changes to taste or texture will be slight.