Why does self-raising flour leave a bitter taste in your baking?

Baking powder is a leavening agent or rising agent. Some others are baking soda, yeast, beaten egg whites and other things. With out it your cookies will be thin, flat, hard and heavy, instead of light and/or crunchy. Baking powder is relatively slow acting, especially when compared to baking soda (sodium bicarbonate). Baking powder is a mixture of baking soda, a base, and cream of tartar, an acid, when mixed with a liquid the two combine and a gas, carbon dioxide,CO2, is released. The tiny bubbles make the dough rise. The liquid is usually added last thing before baking so the bubbles don't just dissipate into the air. The cookies go into a hot oven so the dough begins to set up and the bubbles separate the small particles of firm dough instead of just being baked as bubbles into the otherwise hard cookie.