Actually very easy

Baking powder

The beliefBaking powder is assumed to be a chemical of its own, unrelated to bicarbonate of soda.

The truthBicarbonate plus a dry acid plus starch. Three things, two minutes, all of them already in the kitchen.

Two minutes

How to make it

What you need

1 teaspoon of bicarbonate of soda
2 teaspoons of cream of tartar
1 teaspoon of cornflour

How the engine read this list (3 lines)

5 g	Bicarbonate of soda	baking-soda
—	Cream of tartar	no record
3 g	Cornflour	starch

An empty weight means that line could not be turned into grams — either the amount is open ("to taste") or the ingredient has no record here. Neither enters the sum as zero; they do not enter it at all.

Mix the three in a dry, clean bowl. Both the bowl and the spoon must be dry: a single drop of water starts the reaction in the jar.
Whisk or sift them together thoroughly. Uneven distribution means one part of the batter rises and another does not.
Transfer to a tightly closing glass jar and write the date on it.
Test it before use: a teaspoon into half a glass of hot water should fizz at once and vigorously.

Why it works

Bicarbonate of soda is a base, and meeting an acid it releases carbon dioxide — that gas is what lifts the batter. Use bicarbonate alone and the recipe must supply the acid itself: yoghurt, vinegar, lemon, pekmez, cocoa. Baking powder removes that dependency by carrying a dry acid of its own, cream of tartar or citric acid. The third component, starch, is insurance rather than filler: it takes up moisture from the air and stops the acid and base reacting inside the tin. The ratio is the whole thing — by weight, one part bicarbonate, two parts cream of tartar, one part starch. Add more bicarbonate and the excess has nothing to react with, staying in the crumb as a soapy, metallic taste. That is the familiar bitterness in an over-raised cake.

The rough sum

8 grams going in

11 kcal in total

100% of the mass has figures behind it. This is the sum of what GOES IN rather than of what comes out. Wherever something evaporates, drains or ferments the two differ: a kilo of milk is 150 g of cheese.

Diets it qualifies for

Gluten-free · with care Vegan Vegetarian Lactose-free

Storage & shelf life

How long it keeps

Tightly sealed jar in a dry cupboard: 6 months
Above the hob or anywhere steamy: 1 month
Fridge: Not advised — moisture condenses
Plain bicarbonate on its own: Indefinitely

Baking powder’s enemy is moisture, not heat. Once humid air reaches the jar the acid and base react slowly, and the powder spends its gas before you ever use it — which is why a tin kept on a shelf above the hob is dead in a month. A wet spoon does the same. Writing the date on the jar is a cheaper habit than replacing it every six months: when in doubt the hot-water test takes two seconds and saves a cake.

When to bin it If it does not fizz in hot water, or fizzes weakly, bin it. Bin it if it has clumped, too: clumps mean the reaction has already run inside the jar.

History

Where it comes from

Chemical leaveners are a nineteenth-century invention that changed the kitchen outright: until then the only ways to lift a dough were yeast or beaten egg, both of which take time and skill. Baking powder brought the “quick doughs” — cakes, biscuits, scones. Bicarbonate has a much longer history in Turkish kitchens, used to soften dried pulses, to make biscuits short, and to hold the colour of roasted vegetables. In many households the two words are still used interchangeably, when one needs an acid and the other brings its own — and a surprising share of failed recipes comes from exactly that confusion.

The knack

Without cream of tartar, citric acid works — but not at the same ratio: use half as much as the bicarbonate.
Homemade baking powder is single-acting: it gives its gas the moment it is wet. Get the batter into the oven immediately — every minute of waiting steals rise.
Never add bicarbonate by eye. The excess does not lift anything; it only leaves a soapy taste and a yellowish crumb.

The pantry