In many of my baking recipes I use baking powder together with some other leavening agent (soda or yeast.) This is something that evolved somewhat by accident, but it has worked well for me, so I have stuck with it. I always use Featherweight brand of baking powder. This is a slow acting type baking powder, so it continues to evolve gas late in the cooking process, which helps to keep the batter from falling (as much) as it cooks.

I have found buttermilk to be the best liquid to use for making GF quick breads. The baking soda in these recipes provides a quick acting leavening. In fact, the batter generally begins to rise as soon as the soda is mixed in. This is because the sodium bicarbonate reacts with the acid in buttermilk (or fruit juices) even at room temperature to release carbon dioxide gas. The soda has another important role in recipes with buttermilk. It neutralizes the sour taste of the milk. Thus I proportion my soda to neutralize the buttermilk (1/4 tsp. soda per cup of milk.) And I add extra baking powder to the recipe to maintain leavening as the bread cooks.

The Featherweight baking powder does not contain any sodium bicarbonate, which is what baking soda (Arm and Hammer) is made from. Other brands of baking powder may contain sodium bicarbonate. I do not know what effect using these baking powders will have on my recipes that use buttermilk. Your best indication of a need to adjust the proportions of baking powder and baking soda would be if the batter rises before the soda has been added. This would mean the acids in the batter are reacting with the baking powder you are using. You may need in this case to reduce the amount of soda that you use. I find using too muck soda gives a recipe a harsh bitter taste. If the recipe ends up tasting sour, you need to use more soda.

There is a side benefit of using a fast-acting leavening in GF batters. Often batters have too be fairly thick to come out right, and the leavening makes the batter more workable. That is why I started using yeast in my waffle recipe. The batter that gave the proper texture in the cooked waffle was too thick to spread on the iron. Letting it rise with yeast makes things much more managable.

Charles Fehrenbach, 8/4/2003.