DEBOLINA ROY
Over-creaming butter and sugar
Mixing butter and sugar for too long will create unnecessary air bubbles within the mixture. These weak bubbles may grow too quickly when heated and thus cause an immediate fall or crumble when cooled down.
Excess leavening agents
Excess use of baking powder leads to excessive gas formation, which is beyond the capacity of the dough. On the other hand, expired baking powder fails to create the required reaction that is needed for the cake to rise.
Over-softened butter
Butter that has melted above 68°F makes the air cells unstable and frothy when mixed. One of the main reasons why your cake is sinking is because of the unstable emulsion formed, which leads to a breakdown of the structure of your sponge cake.
Opening the oven door prematurely
If you peek into your oven too early, cold air will barge in and suddenly drop the temperature inside. This rapid heating and cooling can cause trouble for the air bubbles that had not yet stabilized thanks to the gluten and egg proteins.
Over-beating the final batter
Excessive mixing of dry and liquid ingredients results in the introduction of undesired air as well as gluten being overdeveloped. Although you may not realize it, over-mixing is one of the reasons why your cake is sinking.