Prepare the coffee and let it cool for a while - it should be lukewarm before you use it. Start by separating the egg yolks and whites. Combine the yolks with the coffee, oil and lemon zest mixture and whisk it all together. Sieve the flour and starches along with the yeast, sugar and vanillin to make the mixture even softer and fluffier. Add a pinch of salt to the egg whites and whip for around five minutes, until stiff peaks form in the mixture. After whipping the egg whites, add them to the mixture; remember to fold them in from the bottom up to stop lumps from forming. Grease some single-serve chiffon cake moulds and pour about 100g of mixture into each. Then bake the cakes for 35 minutes at 150°C (300°F).