There would be an acidic element to punch up the earthiness of the mushrooms, perhaps lemon, tomato, or even vinegar. (thelunacafe.com)
Baking powder is actually baking soda (sodium bicarbonate) with an acidic element (usually cream of tartar) and cornstarch that prevents clumping. (mjskitchen.com)
Ingredients such as buttermilk, molasses, lemon, vinegars, yogurts, and chocolate are some of the acidic elements used in baking to react with baking soda. (mjskitchen.com)