Every fluffy fairy cake starts with a little white powder.
Bicarbonate of soda and baking powder both release carbon dioxide, but they need different triggers. Knowing which one a recipe uses, and why, explains most flat or soapy bakes.
Pick the kind of recipe to see which raising agent usually does the work. The bar shows how much the recipe leans on bicarbonate of soda rather than baking powder.
General kitchen chemistry from university and Royal Society of Chemistry teaching sources. Always follow a tested recipe's own amounts.
TWO NUMBERS WORTH KNOWING
A little goes a long way.
One figure on strength, one on the heat that sets bicarb off.
4× stronger
Leavening power, bicarb vs baking powder
North Dakota State University Extension says baking soda has four times the leavening power of baking powder, and about 1/4 teaspoon of soda is enough to leaven a cup of flour.
STRENGTH · NDSU EXTENSION
≈ 80°C
Where bicarb starts to break down
McGill's Office for Science and Society puts the minimum temperature for the heat reaction at around 80°C (180°F), well below normal baking temperatures.
HEAT · McGILL OSS
With an acid, bicarb releases one molecule of carbon dioxide for each molecule of sodium bicarbonate. With heat alone it takes two molecules to release one, so the acid route gets more lift from the same amount.
FOUR HABITS FOR A GOOD RISE
Light crumb, no soapy taste.
Raising agents are measured in teaspoons, so small slips show. These habits come from the same extension and chemistry sources.
Level the spoon
A heaped teaspoon of bicarb can give heavy or fallen cakes and bitter or soapy-tasting cookies.
Match the agent to the acid
Bicarb needs an acidic ingredient; baking powder is the reliable choice when the recipe has none.
Do not swap one for one
Baking powder holds less bicarbonate per spoonful, and soda needs extra acid. Any swap changes taste and texture.
Do not overmix
Stir cookies and quick breads only until combined: mixing develops gluten and makes them tough.
AI-generated image, not a photograph of a real person or place.
FAST, SLOW AND DOUBLE
When the bubbles appear.
AI-generated image, not a photograph of a real person or place.
Baking powders are classed as fast or slow acting. Slow-acting powders may use acids such as sodium aluminium sulphate or anhydrous monocalcium phosphate, and make little gas until the mixture is heated.
Double-acting powder contains two acids: one dissolves quickly and starts the rise in the bowl, the other works again in the oven. The British chemist Alfred Bird made an early baking powder in 1843, for a wife who could not eat yeast.
Questions
Questions people ask
What is the difference between bicarbonate of soda and baking powder?
Bicarbonate of soda (baking soda) is pure sodium bicarbonate. Baking powder is sodium bicarbonate combined with a powdered acid, so it reacts with moisture and heat without needing an acidic ingredient in the recipe.
Why do some recipes use both?
When a recipe has an acid, bicarb reacts with it. Baking powder may be added too so that some of the acid, for example from lemon juice, is left behind for flavour, while the powder still gives a reliable rise.
Can I use baking powder instead of bicarb?
Only with adjustments. Baking powder contains less sodium bicarbonate per spoonful, so more is needed, and bicarb used in place of powder needs an added acid such as cream of tartar. Taste and texture may change.
Why does my cake taste soapy?
Too much bicarbonate of soda, or not enough acid for it to react with, can leave bitter or soapy flavours. NDSU Extension warns that a heaped teaspoon can also give heavy or fallen cakes.
What are E500 and E503 on a label?
They are raising agents on the UK list of approved additives: E500 is sodium carbonates and E503 is ammonium carbonates. Diphosphates (E450) and calcium phosphates (E341) are listed too.
