The Difference Between Baking Powder and Baking Soda

Both raise baked goods, both are white powders, and both sit on the same supermarket shelf — which is why they are constantly confused. But they are not substitutes for one another, and swapping them wrongly visibly ruins a recipe.

Baking soda: an alkali that needs a partner

Baking soda is sodium bicarbonate — an alkaline compound. On its own it does nothing in a batter.

But when it meets an acid, an immediate reaction releases carbon dioxide — and that gas is what raises the bake.

The acids that activate it in recipes: yogurt, buttermilk, lemon juice, vinegar, brown sugar (which contains acidic molasses), honey, natural cocoa (not Dutch-processed), and fruit juice.

And a crucial point: the reaction begins immediately when soda meets acid and liquid. So a batter containing soda must go into the oven quickly — every minute of delay is lost gas.

Baking powder: self-contained

Baking powder is baking soda + a dry acid + starch packaged together.

The dry acid (usually cream of tartar or calcium phosphate) does not react while dry. As soon as liquid arrives, both dissolve and react.

The starch is there to absorb any moisture in the tin and prevent an early reaction.

Most available baking powder is 'double-acting' — it releases some gas when the liquid goes in, and the rest when the heat rises in the oven. That gives you a far wider time window than soda.

When to use each

Soda when the recipe contains a clear acid:

• Yogurt or buttermilk cake
• Yogurt pancakes
• Chocolate cake with natural cocoa
• Brown sugar cookies
• Banana bread

Powder when there is no acid:

• Cake made with ordinary milk
• Biscuits and scones
• Plain muffins
• Waffles

And many recipes use both together: the soda to neutralise the acid present and deepen the colour, and the powder to guarantee enough rise without depending on the amount of acid.

Quantity: a large difference

Soda is about four times stronger than powder.

The rough rule: a quarter teaspoon of soda per cup of flour, and a teaspoon of powder per cup of flour.

And more soda does not mean more rise — it gives a distinct soapy, metallic taste and a colour darker than it should be, because the excess finds no acid to react with and stays in the bake.

Substituting one for the other

From powder to soda: use a quarter of the quantity in soda, and add an acid — for instance replace some of the milk with yogurt or buttermilk. Without the acid it will not rise.

From soda to powder: use three times the quantity in powder, and reduce or remove the acid if possible — otherwise the taste will be sour and the texture dense.

This substitution is an emergency measure. The result is acceptable rather than ideal, because the acid-to-alkali ratio affects colour and taste, not only rise.

Testing whether they still work

Both lose potency over time, and a bake that will not rise is usually an old tin:

• Soda: half a teaspoon in two spoonfuls of vinegar. It should fizz immediately and vigorously.
• Powder: a teaspoon in a quarter cup of hot water. It should fizz clearly.

If the fizz is weak or slow, throw it out. Powder loses potency faster — around 6 months after opening, while soda lasts a year or more.

Why a bake turns yellow or tastes odd

This is the classic side effect of too much soda. Unreacted bicarbonate stays in the bake and produces:

• A soapy, metallic taste clearly noticeable in the mouth.
• An unnatural yellowish-brown colour — soda accelerates the Maillard reaction.
• A coarse texture with large irregular bubbles.

If this happens, the quantity was probably doubled or the recipe is short on acid.

Why a bake rises then collapses

This happens when the gas forms before the structure has set. The gas lifts the batter, and when it runs out before the protein and starch have firmed, the structure collapses.

Common causes:

• Soda with acid and the batter left standing: the reaction is immediate, so the gas is lost before the oven. Such a batter goes in within minutes.
• Opening the oven door early: the sudden temperature drop stops the gas expanding before the structure sets.
• Too much raising agent: more gas than the structure can hold.
• A cool oven: the structure takes too long to set and the gas runs out first.

Natural raising: air and steam

Not every bake needs a chemical raiser. There are two natural methods that work:

Air: creaming butter with sugar, or whipping egg whites, traps air bubbles in the mixture, and those bubbles expand with heat. Sponge cake depends entirely on this.

Steam: the water in the batter turns to steam and expands powerfully. This is what raises choux pastry (éclairs), puff pastry and croissants — with no chemical raiser at all.

Other things soda does

Outside baking, bicarbonate has uses in cooking because it raises alkalinity:

• Boiling pulses: a pinch softens the skins and shortens the cooking — but too much gives a soapy taste.
• Roast potatoes: a pinch in the boiling water breaks down the surface so it crisps more in the oven.
• Caramelising onion: a small pinch speeds the caramelisation by 10-15 minutes.
• Tenderising meat: a short soak with a pinch of soda changes the meat surface so it turns more tender.

In every one of these cases, the quantity is tiny — a pinch, not a spoonful.