Reader Christine writes:
I have been reading that invert sugar preserves moisture in cakes. Which brings me to my question: Do you make/use your own invert sugar in cakes? For most tortes that I make, I use a basic “sponge” I guess you would call it in English. I use only flour, sugar, salt, vanilla, a little lemon zest sometimes, and eggs—separated—no hot water bath mixing. I have a hard time keeping the sponge layer moist, so I’m curious about what you do to achieve satisfactory moisture in a such a layer cake.
Hey Christine! Since most sponge cakes are leavened solely with egg foam, they can indeed be a little dry. Brushing on a syrup is a time-tested strategy for keeping sponges moist. The syrup need not be an “invert” syrup to be effective. A simple cake syrup will work just as well.
You don’t want to completely soak the cake. Brush on the syrup, dipping the brush whenever it seems dry. Once the whole surface is covered, wait about five minutes, then poke the cake with your finger to see how soft it is. If it isn’t soft enough, add more syrup. Of course you’ll need less for a thin sheet off sponge than for a thick cake layer.
The important thing is not to completely saturate the cake, as that can ruin the texture of the sponge (a tres leeches cake is an exception to this rule). Thanks for the question, Christine!