As a biochemist, I can't resist a question like this one, because the answer isn't "they're basically the same," it's a genuine chemical reaction happening in your bowl.
Baking soda and baking powder both make your baked goods rise, but they don't do it the same way, and swapping one for the other without adjusting your recipe is the fastest route to a flat cake or a bitter, soapy aftertaste.
Here's exactly what each one does, the ratios if you need to substitute, how long they actually last in your cupboard, and why some recipes insist on using both.
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The Chemistry Behind the Rise
This week's reader question: sometimes, baking powder and sodium bicarbonate (also called baking soda or baking soda) are used in cookbooks. Can you use these interchangeably, and where can you buy them?
What Is Baking Soda?
Baking soda is a base. Back to chemistry, a reaction between a base and an acid creates CO2, the air bubbles that cause the batter or dough to rise. Baking soda needs acid and then converts that acid to neutral while forming CO2.
And that gives airiness to your baking. The sour taste disappears (because the acid is converted). So in a recipe with baking soda, you always see an acidic component (vinegar, lemon juice, buttermilk) to start the reaction.
Rule of thumb: Use about ¼ teaspoon of baking soda per 1 cup (120 grams) of flour.
Can You Substitute Baking Powder for Baking Soda?
Yes, you could, but… because baking soda is four times as powerful, you need four times as much baking powder as baking soda. And it should be done very precisely.
Because if you add too little baking powder, your baking will become firm and not airy. If you add too much, you will get a bitter taste. The batter also becomes saltier by adding baking powder. So there are many things to keep in mind, and I wouldn't recommend it.
How Long Does Baking Soda Last?
Baking soda can be stored unopened for two years. Opened, you can keep it in a dry place for up to 6 months.
How to Test If Your Baking Soda Still Works
Place ¼ teaspoon baking soda in a small bowl and mix with three tablespoons of vinegar. If it fizzes, the baking soda is still working.
What Is Baking Powder?
Baking powder is a chemical. A mixture of baking soda with cream of tartar (tartaric acid). Sometimes cornstarch is added to it to react less quickly with moisture from the air.
Baking powder will react with the moisture in your batter or dough. It gives airiness to your final recipe. Never use more baking powder than described in the recipe. Too much creates a bitter taste.
What Does "Double Acting" Mean?
Most baking powders you buy are double acting. The first time it starts working when it comes into contact with moisture, and the second stage begins when it heats up.
Rule of thumb: Use one teaspoon of baking powder per 1 cup (120 grams) of flour.
Can You Substitute Baking Soda for Baking Powder?
Only if acid is present in your batter, such as lemon, buttermilk, or sour cream, act with care. You only use ¼ part of the amount of baking powder as stated in the recipe. Too much gives a soapy, metallic taste.
Though it should be possible, I wouldn't recommend it because some side effects could make your baking turn out wrong. I'll return to that a little later in the blog and give you some tips about better substitutes.
Substitutes for Baking Powder
You get the best result with baking powder, of course, but good alternatives are:
- Make a baking powder by mixing two teaspoons of tartaric acid with one teaspoon of baking soda. This does not keep well, so make it fresh.
- Beat egg white until stiff and add that. The egg white then contains air and makes the baking airy.
- Instead of water or milk, use sparkling water (which also contains carbon dioxide, which provides airiness).
How Long Does Baking Powder Last?
Unopened baking powder has a shelf life of 18 months. Once opened, air (and moisture) can get in; it can be kept for a maximum of 3 months (if your package is stored in a dry place).
How to Test If Your Baking Powder Still Works
Add one teaspoon of baking soda to 3 tablespoons of hot water. When bubbles form, your baking soda is still working.
Quick Conversion Cheat Sheet
- Need baking powder, only have baking soda? Use ¼ teaspoon baking soda for every 1 teaspoon of baking powder, but only if your recipe already has an acidic ingredient (buttermilk, yogurt, lemon juice, brown sugar) for it to react with.
- Need baking soda, only have baking powder? Use 3 teaspoons of baking powder for every 1 teaspoon of baking soda called for.
- Rule of thumb either way: baking soda is roughly 3-4x stronger than baking powder, which is why the amounts look so different.
Why Some Recipes Use Both Baking Soda and Baking Powder
That can be for several reasons.
- The batter has too little acid to make enough CO2, and you need some extra airiness.
- When there is enough acid, but you want to leave a bit of acidity flavor in your baking. For example, a slightly sour lemon flavor in a lemon cake. If you only added baking soda, it would react with the acid, and that acidity would disappear.
- To get your baking nicely browned. The acidity is essential for browning your baking in the oven. By using a mixture, you can get a better color.
This is also why a cookie made with baking soda browns faster and spreads more than one made with baking powder, the alkaline environment speeds up the browning reaction on the surface. If you've ever wondered why two cookie recipes with nearly identical ingredients come out looking so different, this is usually the reason.
In recipes that use both baking soda and baking powder, you can replace the amount of flour with the same amount of self-rising flour.
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