Jennifer asks: I have an old family recipe that states “beat egg yolks and sugar adding coffee mixture during the last 15 min.” How long should I be beating the egg yolks/sugar total? I believe this cake would be a sponge cake.
Baking S.O.S. says: That’s a really tricky question. Without reading the entire recipe, it is difficult to interpret that one line. 15 minutes is a really long time to beat egg yolks & sugar–especially if you were supposed to be mixing them for a while BEFORE the last 15 minutes!
From my experience, the purpose of beating eggs or yolks & sugar together is to incorporate air bubbles into the eggs which in turn helps the cake rise. And it is especially important to beat the eggs properly in a sponge cake because that is the ONLY thing that makes a sponge cake rise! (Some updated sponge cake recipes call for baking powder, but older, traditional recipes do not.) Recipes typically say to WHIP the eggs & sugar (if you have an electric mixer with a whip attachment, that works best) until they are double or even triple in volume. The amount of time that you whip the eggs is less important than the amount of air you whip into the eggs.
I would suggest using the whip attachment and whip the yolks & sugar until they are triple in volume. If the recipe also asks you to whip egg whites separately and fold them into the cake batter at the end, do so very gently and carefully so as not to deflate the air that you whipped into the egg yolks. I generally add the whipped egg whites in 3 stages and fold in very gently.
I hope that helps. Good luck!
Jennifer replies: Your rationale is very helpful. I think my problem was with the folding of the egg whites.
My great-grandmother emigrated to the U.S. from Sweden in the early 1900’s, so perhaps the mention of time in this recipe was due to lack of English for translation and the absence of an electric mixer.