Baking Soda vs Baking Powder: The Difference, and How to Swap Them

Baking soda is pure sodium bicarbonate, a base that needs an acid in the recipe before it makes any gas. Baking powder is baking soda already mixed with a dry acid and a little starch, so it needs only liquid, and most supermarket baking powder gets a second boost from oven heat. Soda is the stronger of the two. King Arthur Baking says to use three times as much baking powder to replace it, and Arm & Hammer, which makes baking soda, puts it at 3 to 4 times as strong. That is why a recipe can call for 1/4 teaspoon of soda and a full teaspoon of baking powder. You can swap one for the other in a pinch, but neither swap is exact.

Baking soda vs baking powder at a glance

• Contents: baking soda is one compound, sodium bicarbonate. Baking powder is soda plus one or two dry acids plus a starch.
• What sets it off: soda needs an acidic ingredient and liquid. Baking powder needs only liquid, and heat as well if it is double-acting.
• Strength: 1 teaspoon of soda does the work of about 3 teaspoons of baking powder.
• Timing: soda reacts the moment it meets acid and liquid. Double-acting powder reacts once in the bowl and again in the oven.
• Texture and colour: King Arthur Baking's shorthand is "soda = spread" and "powder = puff", and the alkaline dough soda leaves behind browns faster.
• Shelf life once opened: 3 to 6 months for both, according to NDSU Extension's food storage guide.

What baking soda is, and why it needs an acid

Baking soda is sodium bicarbonate, chemical formula NaHCO3, according to Wikipedia's sodium bicarbonate entry. King Arthur Baking describes it as a base with a pH of 8. Dry, in its box, it does nothing.

Add an acid and some liquid and it breaks down into carbon dioxide, water and a salt. The carbon dioxide is the gas that lifts a batter. NC State News, in an explainer built on food science professor Keith Harris, gives buttermilk, yogurt and vinegar as typical acids. Paul Adams at America's Test Kitchen adds lemon juice and "perhaps molasses or brown sugar". For most cookies, brown sugar is the one that counts.

Kitchen acids react with soda fast. Wikipedia's baking powder entry notes that before baking powder existed, this made it "critical for the batter to be baked quickly, before the gas escaped." A cake batter leavened with soda alone should go into a hot oven as soon as it is mixed.

Why too much baking soda tastes soapy

Heat alone can break soda down above 80 °C (180 °F), but without an acid it releases only half its carbon dioxide. What it leaves behind is sodium carbonate, which the sodium bicarbonate entry calls strongly alkaline, giving the bake "a bitter, soapy taste and a yellow color." So when a recipe holds more soda than its acid can use up, the leftover shows as a soapy, metallic edge, which is why soda is worth measuring with a level spoon rather than a heaped one.

What baking powder is

Baking powder is baking soda with the acid already in the can. Wikipedia gives a typical formula, by weight, of 30% sodium bicarbonate, with one or more acid salts and a starch making up the rest. That 30% is why soda comes out roughly three times stronger, spoon for spoon: most of a teaspoon of baking powder is acid and starch.

The starch, usually cornstarch, flour or potato starch, soaks up moisture so the acid and the base stay dry and don't react in the can. NC State makes the same point about its fast acid, monocalcium phosphate: it "doesn't react with the sodium bicarbonate while it's dry." The reaction waits for the liquid.

Single-acting vs double-acting baking powder

Single-acting baking powder has one acid and releases all its gas as soon as it is dampened. Double-acting baking powder has two: a fast acid that works in the bowl, and a slow one that waits for the oven. NC State names the second acid as either sodium acid pyrophosphate or sodium aluminum sulfate. Wikipedia calls double-acting "the type of baking powder most widely available to consumers today", and says the second rise makes the time between mixing and baking less critical.

One brand breaks the pattern. Rumford is double-acting with a single acid, monocalcium phosphate. Wikipedia says about two-thirds of its gas comes out within about two minutes of mixing, and the rest only once the batter passes 140 °F (60 °C).

Does aluminum-free baking powder taste different?

Sometimes. In 2015 Cook's Country tested six US baking powders in white cake, cream biscuits and chocolate cookies, as summarised in the Wikipedia entry. Cake height varied by up to 20% between brands, and 30% of the 21 testers noticed a metallic flavour in the biscuits made with brands containing aluminum.

How much stronger is baking soda?

About three to four times. King Arthur works on three: "use three times the amount of baking powder as baking soda." Arm & Hammer's own guide says soda is "about 3-4 times as strong."

For a sense of normal amounts, Wikipedia says 1 teaspoon (5 g) of baking powder raises a mix of 1 cup (120 g) of flour, 1 cup of liquid and 1 egg. Make that liquid buttermilk and the same mix needs only 1/2 teaspoon of baking powder plus 1/4 teaspoon of baking soda, because the buttermilk's acid reacts with the soda and does part of the work.

Baking soda substitute: can you use baking powder instead?

Yes, at three times the amount. King Arthur's conversion:

• 1 teaspoon baking soda = 3 teaspoons baking powder.

The cost is flavour. King Arthur warns that "a slightly bitter, off-putting taste might result from using that much baking powder." Wikipedia adds that in an acidic batter, baking powder's own acids go unused and "often lend an unpleasant taste to food."

The bake looks different as well. Soda cancels the acid in a recipe and tips the dough alkaline. Baking powder carries enough acid for its own soda, so it doesn't push the dough the same way. Expect more rise and less spread, King Arthur's "powder = puff" in place of "soda = spread", and a paler crust.

The swap is gentlest where the soda is small. A recipe with 1/4 teaspoon of soda takes 3/4 teaspoon of baking powder. One with 1 1/2 teaspoons would need 4 1/2 teaspoons, and that is the amount King Arthur's bitterness warning is about.

What happens if you use baking powder instead of baking soda in a cake?

The cake still rises, because baking powder is a complete leavener. What it loses is the neutralising. A cake that calls for soda has an acid in it, such as buttermilk, yogurt or lemon juice, and the soda is there partly to cancel it. Swap in baking powder and nothing cancels the buttermilk, while the powder adds acid of its own. Wikipedia's advice runs the other way for this reason: when a batter is very acidic, "some of the baking powder should be replaced with baking soda." Expect a tangier, paler cake, and use the 3 to 1 ratio rather than a spoon-for-spoon swap.

Baking powder substitute: using baking soda instead

Soda can't replace baking powder on its own, because it has no acid. Give it one and it can. King Arthur gives two versions for each teaspoon of baking powder:

• 1/4 teaspoon baking soda + 1/2 teaspoon cream of tartar + 1/4 teaspoon cornstarch or tapioca starch.
• 1/4 teaspoon baking soda + 1/2 teaspoon lemon juice or white vinegar.

If the recipe already uses buttermilk or yogurt, Wikipedia says the soda needs less added acid, or none. The cornstarch in the first version only matters if you mix a batch ahead, since it is the part that keeps the jar dry. Even so, James Beard's mix of two parts cream of tartar to one part soda was meant to be stirred together just before use, "since the mixture would not keep", according to Wikipedia.

Both versions have limits. Cream of tartar and lemon juice are both fast acids, so homemade baking powder is single-acting: it releases its gas in the bowl and gives no second rise in the oven. Mix, pan and bake without a pause. And the lemon or vinegar version adds a little liquid and a little flavour of its own.

Self-rising flour is the other way out. It has baking powder and salt mixed in, according to King Arthur Baking, so a recipe made with it leaves out its own baking powder and salt.

Why some recipes use both

Because the recipe has enough acid for some soda, but not enough for all the lift it needs. King Arthur's explanation: when a recipe uses both, "there's a good chance there's acid included in the recipe, yet not enough to trigger a full reaction when combined with just baking soda on its own." Paul Adams at America's Test Kitchen says the same: there is "a small amount of acid in the recipe, which will react with the baking soda, but we want more leavening than that provides."

In that pairing the soda has two jobs. It neutralises the recipe's acid, so a buttermilk or brown sugar batter doesn't taste sharp, and it nudges the pH up for browning. The baking powder supplies the rest of the rise with its own acid built in. Wikipedia's buttermilk example above, half a teaspoon of powder beside a quarter teaspoon of soda, is that pairing at work.

Baking soda in cookies: browning and spread

The two cookie recipes on this site leaven with baking soda alone. The brown butter chocolate chip cookies and the pistachio chocolate chip cookies each use 3/4 teaspoon of baking soda to 220 g of flour, with 200 g of brown sugar and 50 g of granulated sugar, and no baking powder at all. The brown sugar is the acidic partner, the role America's Test Kitchen and King Arthur both give it.

In a cookie, soda does more than lift. Miranda Kohout writes in Pastry Arts Magazine that "an alkaline environment slows protein coagulation, so a cookie dough containing baking soda will have some time to spread in the oven", and that "alkaline doughs brown faster and have a weaker gluten structure."

The browning is the Maillard reaction, which Wikipedia's Maillard reaction entry says is "accelerated in an alkaline environment". Its example is the lye applied to pretzels to darken them. It is the same reaction that turns the milk solids amber when you brown butter. In a brown butter cookie, the butter brings browned flavour into the dough, and the soda helps the dough itself brown in the oven.

Spread is the part a cookie recipe has to manage. Both recipes here chill the shaped dough before it bakes: the brown butter cookies for at least 1 hour, or up to overnight, in the fridge, and the stuffed pistachio cookies for at least 1 hour in the freezer. The brown butter recipe's FAQ is blunt about skipping it: "Without a chill the cookies tend to spread thin and greasy." Both then bake at 350°F for 12 to 13 minutes, 2 inches apart, and come out while the centres are still soft. Soda pushes the dough outward, and the chill holds it back.

If you run out of soda halfway through a batch, King Arthur's ratio turns 3/4 teaspoon of soda into 2 1/4 teaspoons of baking powder. Going by the chemistry above, expect puffier, paler cookies with less spread, and maybe a faint bitterness. Cook's Country's 2015 test points the same way: of the six baking powders, the lower-rising ones made the chocolate cookies judged better. Before a day of holiday baking, run the soda test below.

Baking powder in a fried chicken coating

Leaveners aren't only for the oven. The Nashville hot chicken sandwiches on this site put 1 teaspoon of baking powder in the dry dredge, with 1 cup of all-purpose flour, 3 tablespoons of cornstarch and the seasonings, and another teaspoon in the wet mix of buttermilk, egg, hot sauce and pickle juice. There is no baking soda in it. The recipe then works 3 to 4 tablespoons of the wet mix into the flour "to create a flaky texture", rests the coated chicken for 10 to 15 minutes, and fries it at about 350°F for 7 to 8 minutes.

America's Test Kitchen explains the baking powder in its Easier Fried Chicken: "As the chicken fries, the baking powder releases carbon dioxide gas, leavening the crust and increasing its surface area, keeping it light and crisp." The same recipe notes that the small clumps buttermilk forms in the flour "turn ultra-crisp once fried". Double-acting powder suits frying, because the heat of the oil sets off its second acid.

Does baking powder have gluten?

It depends on the starch. Wikipedia lists cornstarch, potato starch and flour as the usual fillers, and a wheat flour or wheat starch would bring gluten with it. If gluten matters, look for a gluten-free claim on the label. Under the FDA's rule, 21 CFR 101.91, a food labelled gluten-free must contain less than 20 parts per million of gluten. Baking soda is a single compound with no starch in it, so the question doesn't arise.

What is baking soda called in Ireland?

Bread soda. The brown soda bread recipe from Odlums, an Irish flour brand, lists "1 tsp Bread Soda" with buttermilk and wholemeal flour. In the UK, Australia and New Zealand the usual name is bicarbonate of soda, and baking soda is the American term, according to Wikipedia. All three names mean sodium bicarbonate, so a British recipe that calls for bicarbonate of soda wants the same box an American one calls baking soda.

How to test baking soda and baking powder

Both lose strength with time, and each test takes a minute. These are from King Arthur Baking (PJ Hamel, 2015-11-05):

1. Baking soda: put 1 tablespoon of vinegar in a small bowl and stir in 1/2 teaspoon of baking soda. It should fizz at once, and hard. If the fizz is gentle or slow, replace the box.
2. Baking powder: put 2 tablespoons of warm water in a bowl and stir in 1/2 teaspoon of baking powder. It "should definitely bubble and foam." Wikipedia's version uses hot water with the same rule: if it bubbles vigorously, it is still good.

The water test also tells the two apart when a jar has lost its label. King Arthur's version is a teaspoon of the powder in a tablespoon of water: if it fizzes, it is baking powder. Baking soda will sit there until it meets an acid.

How to store them, and how long they last

Keep both dry and tightly closed, away from the steam and heat of the stove. Wikipedia names moisture and heat as what make baking powder lose its strength, and calls the date printed on the can "somewhat arbitrary". NDSU Extension's Food Storage Guide (FN579, reviewed January 2023) gives these times:

• Baking powder: 6 to 18 months unopened, 3 to 6 months opened.
• Baking soda: 2 to 3 years unopened, 3 to 6 months opened.

Kansas State University's Safe Food Storage: The Cupboard gives baking powder 18 months or the date on the can, and baking soda 2 years, at 70°F. Arm & Hammer's FAQ gives its baking soda a three-year shelf life, with the date on the bottom of the box. The sources don't agree, so read the date as a rough guide and let the fizz test decide.