Not enough baking soda and/or baking powder or it could be that your baking soda and/or baking powder are old and in need of being replaced. Maybe you need a new recipe. I really like the lemon blueberry muffin recipe at MakeMuffins.net. Check out this recipe at the link listed below. I have never had a problem with these muffins not rising.
One example of a chemical reaction that occurs when baking muffins is the raising agent: the baking soda (whether that in the baking powder or added separately) reacts with any acid in the ingredients (milk, cream of tartar etc) to form a gas and a salt, and the gas bubbles formed result in the rising of the muffins.
Baking soda and baking powder are both chemical leaveners used to make baked goods such as cakes and muffins. Baking soda has some other culinary uses, not discussed here. In recipes calling for baking powder, baking soda can be used, along with some cornstarch and cream of tartar. Baking powder cannot, however, be used to replace baking soda.
Baking powder is useful for mixing into many types of batter and dough as leavening. It already contains an acid, so it does not need additional acid in the batter, as baking soda needs. Some baked good that use baking powder as leavening are Quick Breads, Cookies, Biscuits, Cornbread, Muffins, Pancakes and Waffles.
Baking powder lightens the texture of cakes by enlarging air bubbles within the batter. The correct use of baking powder makes the difference between a light and fluffy cake.Baking powder has different, beneficial properties for cake baking that other types of leavening agents don't have. Yeast produces the same rising action, but takes two to three hours to produce bubbles. Baking powder reacts with water, whereas baking soda requires the use of a liquid acid…
The most common cause of muffins rising then collapsing is removing them from the oven before they are thoroughly baked. Another possibility is that the oven might not hold a steady heat, allowing the temperature to drop during the baking time. Finally, there might be an error in the proportion of ingredients with not enough or too much soda or baking powder.
I haven't tried it but I read if you increase the baking soda. Example if recipe calls for 1 tsp of baking soda, add 2 tsps and they will rise nice and high. It was on a review of a muffin recipe. [Edit; JunioMuffinMan] Careful! If you do that it could affect the taste! try baking powder if the recipe calls for baking soda. I think that instead of putting some baking soda you could…
Baking powder is not the same as baking soda. Baking powder is a 1:3 ratio of baking soda to cream of tartar, which are both raising agents designed for different purposes - one of them is activated by water, the other by heat. Baking soda is "strong" compared to baking powder, and is not a direct substitute for baking powder.