Beating of the whites is perfected.
When folding in the cake mixture and the egg whites is there a specific technique?
I place in about 1/3, fold, 1/3, fold, and the rest using a spatula, and turn the bowl to get it folded evenly.
Do I leave the cake to cool in the oven with the door open ajar? And for how long?
Or is there a specific way to cook it, e.g. high temp then low temp?
Many sponge cake forms are made with removable bottoms and tabs that stick up on the sides.
The purpose of the removable bottom is obvious, run a knife around the side and push the cake out. However, the tabs allow for a marvoulous technique when cooling your sponge cake.
When your cake is done cooking and ready to let cool, you invert it without running your knife around the edge. The tabs keep the pan above the table/rack and allow for the air to circulate. Gravity helps to maintain the height of the cake because the cake is still stuck to the bottom and sides of the pan. As it cools, the little stretching action from gravity gives you a higher/fluffier product.
It doesn't completely solve your shrinkage issue but it helps out allot.
You are using a bundt or tube pan, yes? A chiffon cake will need the extra support in provides, and after taking it out of the oven it should be inverted until completely cool. A bottle can make a good cooling rack, just put the hole of the pan around the neck and put it somewhere it won't be knocked over. Cooling in the oven is good too.
