If you have self-rising flour left over from another recipe—can you use it in muffins if you leave the leavener out?
Muffins can be leavened with baking powder, with baking soda, or with a combination of the two. We tested muffins in each category. For recipes that called for just one leavener, we tested the original recipe alongside the same recipe made with self-rising flour and no other leavener. For the muffins that contained both powder and soda, we tested the self-rising flour substitution in two ways: with self-rising flour and no added leavener at all, and again with just the baking powder omitted because self-rising flour contains baking powder but not baking soda. With self-rising flour in place of both powder and soda, the muffins came out slightly squat as well as pale and doughy-looking (baking soda helps with browning in addition to leavening). When used in tandem with baking soda, self-rising flour delivered muffins that were properly browned, but the domes still looked deflated and one batch had a flavor tasters described as “metallic” or “chemical-y.” In recipes that called for only baking powder, self-rising flour didn’t foul up the browning, but the muffins were still slightly squatter and much saltier than when made with all-purpose flour and baking powder. (The saltiness surprised us, but we should have looked more closely at the ingredient list on the package: Self-rising flour also contains salt.) The baking powder–only batch was the most promising, so we tried it one more time with self-rising flour, this time leaving out the salt as well as the baking powder. Though only one taster found the muffins overly salty, the domes were still squat. Not exactly what we would call a success.
THE BOTTOM LINE: Don’t use self-rising flour in recipes that don’t call for it.