What’s the Difference Between Baking Soda and Baking Powder?
Ask Science explores the science behind why substituting baking powder with baking soda is a no-no when making muffins.
Have you ever made a mistake in a recipe and wondered just what went wrong?
Once, I was making muffins and instead of adding baking powder, I added baking soda. I thought this was no big deal, since I knew both of these powders were supposed to make dough rise. Much to my surprise however, my muffins still came out like hockey pucks. So what went wrong? What’s the difference between baking soda and baking powder? Was there anything I could have done to save my poor muffins? Let’s look at the science behind the recipe.
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Rise Up
The first clue to unlocking the mystery of my flat muffins is understanding what baking powder and baking soda are made of. Baking soda’s name sounds a bit misleading. After all, it’s a powder, not a fizzy drink.
As I mentioned in my episode about baking soda and vinegar cleaners, baking soda also goes by the names sodium bicarbonate, bicarbonate of soda, and sodium hydrogen carbonate. The origins of the “soda” part of baking soda’s name are shrouded in history and legend, but most etymological dictionaries I consulted said that the name is derived from the Italian word “sida” which referred to a kind of plant from which baking soda was originally made.
Regardless of where the name came from, baking soda is a base. This means that when it is mixed with an acid, it undergoes an acid-base reaction. Most importantly for my muffins, this reaction releases carbon dioxide gas. That gas gets caught in the gluten matrix of the dough, causing the dough to rise.
So now that we know what baking soda is, let’s take a look at its close cousin, baking powder…..
The Power of Powder
Unlike baking soda, which is just a base, baking powder contains a base (baking soda) and a powdered acid mixed together. In order for the two chemicals to start their acid-base reaction and give off carbon dioxide, all they need is a little liquid.
If you take a close look at recipes that call for baking soda instead of baking powder, you’ll probably notice that the liquid portion of the recipe is some kind of acid. Most fruit juices, (especially lemon juice), vinegars, and buttermilk are acidic. Having any of these ingredients in your mix gives the baking soda the acid component it needs to start the acid-base reaction.
On the other hand, if you have a recipe that uses baking powder, the acidity of the liquid component doesn’t matter. In baking powder-only recipes, you’ll typically see more neutral liquids like milk or water. (Milk is slightly acidic, but just barely.)
We Need a Substitution
Now we can figure out what went wrong in my recipe. By adding baking soda and milk together, all I get is soggy baking soda. Since the milk wasn’t acidic enough to cause the acid-base reaction to take place, the carbon dioxide wasn’t produced, and my dough never rose, leaving me with hockey pucks instead of muffins.
What could I have done to save my recipe? Well if you’ve ever checked the “Emergency Substitutions” section of your favorite cookbook, you know that if you don’t have buttermilk, you can combine a little lemon juice with milk and use that instead. That isn’t because lemon juice and milk together taste anything like buttermilk, it’s because the lemon juice lowers the pH of the milk to around the same level as the pH of buttermilk.
Another substitution that I could have used to save the day is cream of tartar. That’s because cream of tartar is an acid, typically in powdered form. That means that when we add cream of tartar and baking soda to our mix, we have both an acid and a base in powdered form, just like we get with baking powder. So all our mixture needs to generate carbon dioxide is a liquid.
Conclusion
So now you know a little more about the differences between baking soda and baking powder, why you would choose one over the other, and some of the chemistry behind some emergency substitutions. You also know that you should probably avoid having me cook muffins for you.
If you want to know more kitchen chemistry, I highly recommend the excellent book, What Einstein Told His Cook by Robert Wolke (no relation to the Ask Science podcast).
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Home made muffins image, Selma Broeder at Flickr. CC BY 2.0. Baking powder courtesy of Shutterstock.
About the Author
Dr. Lee Falin earned a B.S. in Computer Science from the University of Illinois, then went on to obtain a Ph.D. in Genetics, Bioinformatics, and Computational Biology from Virginia Tech.
