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What's the Difference Between Baking Soda and Baking Powder?

Everyday Einstein explores the science behind why substituting baking powder with baking soda is a no-no when making muffins. 

By
Lee Falin, PhD,
November 4, 2013
Episode #075

Page 2 of 2

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 Everyday Einstein podcast). 

If you liked today’s episode, you can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.

Home made muffins image, Selma Broeder at Flickr. CC BY 2.0. Baking powder courtesy of Shutterstock.

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