Sponge cake calculator
A sponge that rises on beaten egg alone: 400 g of egg takes 140 g of cake flour, 150 g of sugar and 50 g of potato starch. No baking powder.
A sponge is eggs, sugar and flour. Everything that lifts it is air beaten into the eggs, so the whole recipe comes down to two things: beat properly, then fold the flour in without knocking the air back out.
How it works
Counted from the eggs
100% here is egg, because that is how a sponge gets planned — you have seven eggs and want to know what goes with them. AniaGotuje states the weight out of the shell, 400 g for seven larger eggs, and adds 140 g of cake flour (35%), 150 g of sugar (37.5%) and 50 g of potato starch (12.5%).
Starch alongside the flour
Starch dilutes the gluten. The same weight of flour, with a quarter of it as potato starch, gives a softer and less chewy crumb. Moje Wypieki splits it almost identically: 115 g of wheat flour to 45 g of starch.
No baking powder
Neither source uses any. The volume is all foam, which is why the eggs and sugar are beaten for at least ten minutes and the flour is folded in by hand. AniaGotuje’s génoise does the same with whole eggs warmed over water, and comes out heavier: 63% flour and 53% sugar.
Sources & methodology
Every percentage in this calculator traces to the published sources below — nothing is invented. Where respected sources disagree, the default sits inside the documented range.
- AniaGotuje — uniwersalny biszkopt do tortów — The anchor, and it states the egg weight out of the shell — 7 eggs as 400 g / 140 g cake flour (35%) / 150 g sugar (37.5%) / 50 g potato starch (12.5%), one 26 cm tin.
- AniaGotuje — biszkopt genueński — The sweet end of the sugar band, also weighed: 6 eggs as 380 g / 200 g sugar (53%) / 240 g flour and no starch at all.
- Moje Wypieki — biszkopt — Counts eggs rather than weighing them, so it anchors nothing — cited for the same flour-to-starch split (115 g : 45 g) and for dropping the hot tin from 30 cm.
FAQ
How many eggs for which tin?
400 g of egg, roughly seven, fills a 26 cm tin. The génoise at 380 g goes into 24 cm, and Moje Wypieki’s five-egg sponge into 23–25 cm.
Why did the sponge sink?
Steam left inside pulls it down as it cools. Moje Wypieki gives the counterintuitive fix: drop the hot tin onto the floor from about 30 cm the moment it leaves the oven. The impact knocks the steam out before it does damage.
How much sugar does it actually need?
37.5% of the egg weight in the everyday sponge, 53% in the génoise. Sugar holds the foam up, so going lower costs height as well as sweetness.
Which flour?
Cake flour, the finest and weakest wheat grade, plus potato starch. Both recipes use exactly that pair.