A tall sponge that doesn't sink: ratios, whipping to the 'ribbon' stage and the truth about baking soda
Why sponge cakes sink and turn dense: the classic egg-sugar-flour ratio, how to tell the eggs are whipped enough, why starch helps, when you can open the oven, and whether soda needs to be 'quenched' with vinegar.
Where the rise comes from
A classic sponge has no baking powder or soda. It rises only thanks to the air you whip into the eggs. In the oven the air bubbles expand, and the egg protein around them sets and fixes the porous structure.
Hence the two main rules: whip in as much air as possible, and don't lose it while you fold in the flour and get the tin into the oven.
The classic ratio: 1 egg — 25–30 g sugar — 25–30 g flour
Remember the ratio 'per egg' and you can make a sponge of any size without a recipe. A 20–22 cm (8–9 in) tin takes 4 eggs; a 24–26 cm (10 in) tin takes 5–6.
For an extra-tender sponge, replace 20–25% of the flour with starch. Starch forms no gluten, so the crumb comes out softer and airier.
Secret #1: warm eggs and the ribbon stage
Room-temperature eggs whip up to 1.5–2 times more volume than cold ones. Take them out of the fridge an hour ahead, or leave them in warm (not hot) water for 5 minutes.
Whip whole eggs with sugar on high speed for 8–10 minutes. Don't worry about overdoing it — under-whipping is much worse. The mixture should turn almost white and triple in volume.
Secret #2: sift the flour and fold by hand
Sift the flour and starch twice: it gets aerated and won't form lumps that you'd later have to stir out, knocking bubbles out of the batter.
Fold the flour in 2–3 additions with a silicone spatula, not a mixer. Move from the bottom up along the side of the bowl, turning the bowl as you go. Stop as soon as there are no dry streaks. Every extra stroke pops bubbles and makes the sponge denser.
Secret #3: the tin and the oven
Line only the base of the tin with parchment and don't grease the sides. The batter clings to dry sides and climbs higher; on greased sides it slips and sinks.
Preheat the oven properly, at least 15 minutes. Put the tin in as soon as the batter is ready — the bubbles won't wait.
Don't open the oven for the first 20–25 minutes. A rush of cold air is the main reason sponges collapse. Check at the end with a wooden skewer: it should come out of the centre dry.
Secret #4: cooling and resting
A sudden temperature drop can also sink a sponge. When it's done, turn off the oven and leave the sponge inside with the door ajar for 10 minutes. Then take it out and cool it in the tin on a rack.
A professional trick: wrap the cooled sponge in cling film and leave it for 6–8 hours or overnight. The crumb settles, stops crumbling, and slices easily into even layers.
Baking soda, baking powder and the vinegar myth
Muffins, apple cakes, pancakes and kefir- or buttermilk-based bakes need baking powder or baking soda. Soda is an alkali: to release gas it needs an acid. So it's used in batters with kefir, buttermilk, sour cream, yoghurt, honey or cocoa. Baking powder already contains both soda and acid and works in any batter.
'Quenching' soda with vinegar in a spoon is pointless: the gas is released right there in the spoon and escapes before it ever reaches the batter. The right way is to mix soda into the flour and let the acid in the batter do its job in the oven.
- Baking powder: 1 tsp (4–5 g) per 150–200 g flour.
- Baking soda: ½ tsp per 250 ml kefir/buttermilk or 200 g sour cream.
- Too much soda — bakes taste bitter, darken and smell soapy.
Why the sponge sank or turned dense
Go through the list:
- The eggs weren't whipped to the ribbon stage.
- The flour was mixed in with a mixer, or for too long.
- The batter sat before baking.
- The oven was opened in the first 20 minutes.
- The sponge was underbaked — a raw middle sinks as it cools.
- The oven was too hot — the top set, the middle rose and cracked into a dome.
- The sides of the tin were greased.
Questions and answers
How long should I whip eggs for a sponge?＋
8–10 minutes on high speed, to the ribbon stage: the trail from the falling mixture sits on the surface for 2–3 seconds.
Does a sponge need baking powder?＋
A classic one doesn't — it rises on whipped eggs. If the eggs are whipped well, no baking powder is needed.
Why did my sponge sink after baking?＋
Most often it was underbaked, the oven was opened too early, or it cooled too fast. Leave it for 10 minutes in the switched-off oven with the door ajar.
Should I quench baking soda with vinegar?＋
No. The gas is released in the spoon and escapes. Mix the soda into the flour — the acid from kefir, buttermilk or sour cream will work in the batter.
Try it in practice
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