Baking Soda vs Baking powder, Part 1

Aluminum-Free Baking Powder

Aluminum-Free Baking Powder

By Cat, Nov 2014 (Photo, right, from Wikimedia Commons)

Baking soda and baking powder are leavening agents for quick-breads, muffins, cakes, and cookies. But what is the difference between them? How do you know which to use and how much to use? How do you convert from one to the other?

Baking soda vs Baking powder

Both act to leaven a batter or dough by reacting with acid in the liquid to produce carbon dioxide (CO2). The CO2 forms bubbles as it is trapped in the batter yet trying to rise out of the batter, thus causing the batter to rise with it. The difference between these two leavening agents and modern improvements to baking powder has to do with the acid:

  • Baking soda needs an acidic ingredient in the batter to activate its leavening quality. In other words, the recipe must contain an acidic liquid such as lemon/orange juice, buttermilk, sour milk, yogurt, liquid whey, or vinegar, or moisture and/or an acidic powder such as cream of tartar (potassium bitartrate).
  • Baking powder is a combination of baking soda and a weak acidic powder (such as cream of tarter, sodium phosphate, monocalcium phosphate, or an aluminum salt). It is activated when it encounters any liquid in the recipe – an acidic recipe ingredient is not needed (only moisture is needed to activate, because the acid is part of the baking powder). Baking powder also includes a powder (usually GMO cornstarch or potato starch) to absorb humidity so that it doesn’t activate before you add it to a recipe (more on this, below). You can also make your own; see recipe below.
  • Double-acting baking powder is activated in two stages: Stage 1 begins as soon as you add the baking powder to the moist batter; the baking soda and cream of tartar interact to form the leavening CO2 bubbles. Stage 2 begins when you expose the batter to heat, which activates another weak acid (such as sodium aluminum phosphate) to react with any remaining baking soda. This forms more of the leavening CO2 bubbles, and enhances the original bubbles for more of a rise. (6)
  • Aluminum-free double-acting baking powders use monocalcium phosphate as the weak acid; upon mixing into the dough, part of it is converted to dicalcium phosphate which remains dormant until exposed to the heat of the oven; the remainder reacts almost immediately upon mixing with the baking soda for Stage 1; the dormant salt is activated by the oven’s heat to react with more of the baking soda for Stage 2.

The key to successful leavening is to have sufficient acid to release CO2 from the soda. Both baking soda and baking powder provide the soda; but soda requires the addition of sufficient acid, while baking powder contains sufficient acid to activate the leavening. Thus, a recipe that:

  • Includes acidic ingredients (such as buttermilk) work best with baking soda, or a combination of baking soda and cream of tarter if more acid is needed.
  • Does not include acidic ingredients (or insufficient acid) must use baking soda plus cream of tartar (or baking powder, which includes both the soda and the weak acid).

Simple Conversions

While baking powder includes baking soda, its potency is diluted by the addition of an acidic powder and a moisture-absorbing powder. 1 tsp baking powder includes 1/4 tsp soda, 1/2 tsp acidic powder and 1/4 tsp de-moisturizing powder. Thus baking soda has 4-times the amount of leavening power per teaspoon than baking powder. However, most guides recommend for simple conversions to use a factor of 2 rather than 4. Thus:

  • Baking soda to baking powder: You need at least twice as much baking powder as baking soda, so use double the amount. For example, for a recipe that calls for 1 tsp baking soda, you would need at least 2 tsp baking powder.
  • Baking powder to baking soda: You need half as much baking soda as baking powder, so halve the amount.  If your recipe does not already include an acidic ingredient (buttermilk, sour milk, yogurt, kefir, lemon or other citrus juice), you need to add 2 parts cream of tartar for every 1 part of baking soda, to activate the soda. For example, for a recipe that calls for 1 tsp baking powder, you would need 1/2 tsp baking soda plus 1 tsp cream of tartar.

Important Concerns about Baking Powder

Shelf Life

Baking soda has an indefinite shelf life, but baking powder does not.

Because baking powder contains both the soda and the acid necessary for leavening, all it needs is a bit of moisture to turn the soda into CO2. Once that happens, it has lost most or all of its leavening power. For this reason, a moisture-absorbing ingredient (usually cornstarch) is added to commercial baking powder.

Yet every time you open the container of baking powder, it is exposed to moisture in the air; eventually the moisture-absorbing ingredient is saturated, and any additional moisture will activate the soda, releasing CO2. It will not take long for all the soda to be used up.

Pure baking soda, on the other hand, does not include the acid, so cannot be activated to form CO2 until it is added to a batter that includes an acid.

Avoid aluminum, a toxic heavy metal, in baking powder

Most double-acting baking powder includes an acidic aluminum salt (sodium aluminum sulfate) which causes the leavening to act in two stages, and gives you a 10 – 15 minute window before putting the batter in the oven:

  • Stage 1 begins as soon as you add the baking powder to the moist batter; the baking soda and cream of tartar interact to form the leavening CO2 bubbles. (6)
  • Stage 2 begins when you expose the batter to heat, which allows the aluminum salt to react with any remaining baking soda and form more of the leavening CO2 bubbles, and enhance the original bubbles for more of a rise. (6)

Unfortunately, aluminum is a toxic heavy metal; as such, it should be avoided, as heavy metals build up in the body, becoming worse and worse as time goes on.

If you must use baking powder, choose an aluminum-free brand such. While most aluminum-free brands types are not double acting (so you need to get the batter into the oven as soon as possible), Bob’s Red Mill and  Rumford are exceptions. The low-acid monocalcium phosphate provides the double-acting function

Avoid GMO cornstarch

Furthermore, as of this writing, Bob’s Red Mill and  Rumford are also GMO-free (Rumford states on the container’s list of ingredients, “Cornstarch (from nongenetically modified corn);” Bob’s Red Mill has their non-GMO policy on their web site (9)).

If your favorite product does not identify as GMO-free or 100% Organic, you cannot be sure it does not contain GMO cornstarch. In that case, a better option is to make your own baking powder at home (see below).

Homemade baking powder

If you don’t like to do the math each time you use a recipe that calls for baking powder, it is easy to make up a small batch of homemade baking powder, enough to fill a half-pint Mason jar. In the instructions below, the basic formula for each ingredient is followed by the half-pint jar recipe amounts.

Using Organic/non-GMO cornstarch (makes 16 Tbsp baking powder), mix and store in a half-pint sealable container:

  • 1 part baking soda (4 Tbsp),
  • 2 parts cream of tartar (8 Tbsp),
  • 1 part Organic cornstarch (4 Tbsp)

Using arrowroot (makes 15 Tbsp baking powder), mix and store in a half-pint sealable container:

  • 1 part baking soda (3 Tbsp),
  • 2 parts cream of tartar (6 Tbsp),
  • 2 parts arrowroot powder (6 Tbsp)


  1. Joy of Baking (
  2. Fine Cooking article by Brian Geiger (
  3. Fine Cooking article by Shirley Corriher (
  4. Chemistry About: How to substitute baking powder and baking soda (
  5. Baker Bettie (
  6. Serious Eats’ Food Lab (
  7. Decoding Delicious (
  8. Nourishing Traditions recipe for pre-soak cornbread, by Sally Fallon with Mary G. Enig, PhD.
  9. Bob’s Red Mill non-GMO policy (blog.bobsredmill. com/featured-articles/our-policy-regarding-gmos) (link deactivated at their request)

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