Most people don’t know that baking powder is best combined with flour first then mixed with wet ingredients.
There are two categories: Single-acting and double-acting baking powder. While single acting baking powders produce gas when mixed with water, double acting baking powders, which are mostly commercial, produce small amounts of gas when mixed with liquid.
Gas generation occurs when the batter is heated during cooking. Because baking powder is a blend of acid and alkali, high altitude can affect the amount needed in a recipe. With that in mind, you would need to reduce the quantity of baking powder when baking in high altitude areas.
Baking powder loses potency over time so, in my view, expiry dates on baking powder should be taken with a pinch of salt. Once you open a pack, make sure to store the contents in an airtight container.
A test to verify the potency: pour 1/3 a cup of hot water over a teaspoon of baking powder in cup. If the mixture bubbles enthusiastically, your baking powder is good for use. If it does not, it belongs in the trash can.
It costs Sh15 or more for 100g depending on size and brand.