just made a batch of peach muffins. The receipe calls for baking powder no baking soda. Question is why are some receipes usung baking powder and soda together. What does the combo do to the muffin? The muffins taste okay, but I was reviewing some other muffin receipes and notice the difference?
If there's enough acidic liquid, it works to just use baking soda. A good example is a buttermilk pancake or biscuit recipe. Or if there's no acid, use baking powder (roughly at the 1tsp/ cup flour ratio). Many muffins fall in between, with some acid from the fruit, fruit puree, or molasses. There might not be enough acidity (or it is too variable) to depend entirely on baking soda. Hence it is easier have enough baking powder to do the real work, and some baking soda to 'balance' the acid. Hence the variability.
In most cases we don't know if this aspect of the recipe has been carefully tested, or whether the author is just working from some rule of thumb.
baking soda is alkaline--it needs to come into contact with an acidic or sour ingredient (sour cream, yogurt, etc., as antilope says, lemon juice, vinegar, etc.) in order to set off the chemical reaction that produces the leavening, lifting/puffing effect.
baking powder contains both acidic and alkaline/basic components, and it only needs to come into contact with liquid and/or with heat to produce the leavening effect (the creation of carbon dioxide gas).
i guess when recipes use both, the recipe author wanted the baking soda to interact with the acidic ingredients, and then to get extra lift on top of that with the baking powder.
but in the end both powder and soda wind up doing the exact same thing--they produce carbon dioxide gas to leaven the muffin. if you use the correct amount you'll get the maximum lift. some recipes call for way, way to much leavening, and that can make whatever you're baking puff up and then collapse, making it very dense.
here's a good rundown of the baking soda vs. baking powder distinction and the correct proportions to use per cup of flour.
That's a good clip. I love Shirley Corriher. I don't know about the different types of acids used in baking powder and their reaction times so could never go by that in picking baking powders but in the end, she suggests Clapboard Girl bp because it reacts more in the heat and that gives you more time to get it in the oven. That's far more helpful to me, as a nonchemist, than knowing if it's aluminum disulfate or whatever is in the baking powder.
Anyway, as the OP goes, baking soda is much stronger and more immediate of a reaction whereas baking powder gives you time because it'll also react in the heat of the oven. While baking soda needs acid, an acidic batter will work fine with baking powder so if a recipe calls for baking soda, theoretically four times the baking powder will work (although I'd reduce the flour some then). But, you can't use baking soda for baking powder without adding an acid.
Usually when a recipe calls for baking soda it also has sour cream, yogurt, sour milk or buttermilk as an ingredient. The baking soda is to counter balance the acid in those other ingredients.
Also, according to Cooks Illustrated, using baking soda in place of baking powder created a coarser crumb in one of their recipes.