I bake sponge cake from a recipe in an old cookbook - I seem to be doing everything right, but it always sinks and becomes dense after I take it out of the oven. What could be causing this?
You can't really save a sponge cake that's already collapsed after baking - it's too late by then, because the damage comes from mistakes made during mixing and baking. But here's what people often miss: the temperature of your ingredients before you start whisking matters hugely. Eggs should be at room temperature, not straight from the fridge - cold eggs take longer to whisk and don't get as fluffy, plus the air bubbles end up bigger and less stable. When the batter heats up in the oven later, these bubbles burst unevenly, and the cake sinks.
The second thing that gets forgotten in a lot of old recipes is baking time and temperature. If your oven is too cold or heats unevenly, the batter takes forever to warm through and the structure doesn't set before the moisture starts evaporating. So the top looks done but the inside is still wet and unstable. Try preheating your oven about 20 minutes before you put the cake in, check the actual temperature with a thermometer (the dial often lies), and watch carefully - the brown crust will appear 5-10 minutes before it's completely done.
As for cooling - yeah, a sudden chill will make it worse, but that's just a secondary issue. If your batter was whisked properly and baked well, it'll handle a quick temperature change just fine.
A sponge cake usually collapses because of sudden temperature changes - when you pull it out of the oven, the batter shrinks and loses its airiness. Try not taking the cake out onto a cold surface. Instead, leave the pan on a rack right in the oven with the door slightly open for about 10-15 minutes so it cools down gradually. Also make sure your batter is beaten well (the egg whites should hold their peaks) and don't open the oven door while it's baking - even once can let all the air out.
The problem often isn't the cooling, but that the sponge cake is underbaked inside. Check if the center goes through with a thin stick - if the batter sticks, give it a few more minutes in the oven. Old recipes sometimes give less time than modern ovens actually need. And here's the important part: don't open the oven door for the first 20-25 minutes, or the cake will definitely collapse from the pressure drop - no towels around it will save it.
The thing is, you can't always "save" a sponge cake after it's baked - the problem starts earlier. Those guys are right about underbaking and temperature shock, but they're missing the main thing: if you're whipping eggs by time using an old recipe instead of whipping to the right consistency, the air bubbles will be too large and unstable. They escape when it heats up, and the cake sinks. Try whipping your eggs with sugar for longer than usual - the mixture should double in volume and turn almost white.
A microwave for cooling sounds weird, but try this: take the cake out still in the pan and leave it on the oven rack for like 10-15 minutes while the oven's still a bit warm. Then move it to the table. Yeah, sudden cold does kind of "shock" the batter, but what's way more important is that old recipes are often designed for smaller ovens or different humidity levels - add like 5-7 minutes to the baking time listed and check it more often with a toothpick. I had the same problem before I realized I was just underbaking it.
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