Baking powder
A complete chemical leavening system: bicarbonate of soda, one or more acids, and a starch to keep them apart until wetted.
Baking powder is bicarbonate of soda with its acid already supplied, plus a starch filler that keeps the two dry and separate in the tin.
That completeness is the entire difference between it and bicarbonate of soda, and it is why the two are not interchangeable. Baking powder brings its own acid, so it works in a batter with no acidic ingredient. Bicarbonate of soda does not, and needs one present.
Most baking powder sold today is double-acting: one acid reacts on contact with liquid and another only on heating. The practical effect is a reserve of lift held back until the batter is in the oven, which makes it considerably more forgiving of a delay between mixing and baking.
Composition and specification
Components
Bicarbonate of soda as the carbon dioxide source, one or more acid salts, and a starch to absorb moisture and prevent premature reaction in storage.
RecordedPaula Figoni, John Wiley & Sons
What changes if it is left out
A chemically leavened batter without it will not rise meaningfully. It cannot be replaced by bicarbonate of soda alone unless an acid is also added, and the quantities are not equivalent.
Unsourced because it follows directly from the composition described above, which is cited. BakeHQ deliberately publishes no substitution ratio: the correct amount depends on how much acid the formulation already contains, which no single number can capture.
RecordedFollows from evidence recorded elsewhere on BakeHQ
Storage and deterioration
Loses potency with age and on exposure to humidity. Activity can be checked by adding a spoonful to hot water and observing whether it fizzes vigorously.
Note that this test uses hot water rather than cold, because a double-acting powder’s second acid is heat-activated and cold water will under-report its activity.
RecordedEstablished practice, not a measured result
Related
Used in
A complete leavening system is used because a muffin batter has no reliable acid of its own.
Gas is released early, which is why a scone needs an oven that is already hot to set the structure before it escapes.
Acting once and immediately, which is why the batter goes into the oven as soon as it is mixed.
The only source of gas.
What it does
Aeration
Releases carbon dioxide in two stages in most modern powders, holding some lift back until the batter is in the oven.
Can stand in for
Possible but not gram for gram: baking powder is diluted by its own acid and starch, so more is needed, and the recipe’s own acid is then left unreacted — which changes both flavour and colour. BakeHQ does not publish a single ratio because the right amount depends on how much acid the formulation contains.
Compared in
Baking powder vs bicarbonate of soda
One side of the comparison readers most often arrive with.
One side of the comparison, so the comparison is reachable from the record a reader is more likely to land on first.
Commonly confused with
Routinely treated as interchangeable. One brings its own acid and the other does not, which is the whole difference and the source of most chemical-leavening faults.
Can be replaced by
Eggs— for aeration only, when whisked to a foam
A whisked egg foam can aerate a batter that would otherwise need a chemical leavener — but it supplies none of the pH change, and the substitution fails entirely if the eggs are not whisked. Scoped so the conditionality is part of the record rather than a caveat in prose.
With bicarbonate of soda, and not alone. The pair is effectively home-made baking powder and reacts as soon as it is wetted, so it has no delayed second action. BakeHQ publishes no ratio.
Covered in
What freezes well, and what freezing actually does
Why raw batter freezes badly: the powder starts reacting the moment it is wetted, so a thawed batter has already spent part of its lift.
History and culture
When baking stopped needing time
The refinement that made the reaction independent of the rest of the recipe.