If your chiffon cake collapsed or deflated after being taken out of the oven, it could be for a few reasons:  - The egg whites weren't beaten to stiff peaks. Under beating the egg whites can lead to an unstable cake.  - You used a non-stick pan or greased the tube pan. The cake needs to cling to the sides of the ungreased tube pan in order to rise properly without collapsing in on itself.  - You didn't flip the cake pan over soon enough. As soon as the cake comes out of the oven, you must invert it onto a wire rack. This prevents the cake from collapsing.  - You didn't bake the cake for long enough. Underbaked cakes will fall in the middle, even if you followed the recipe correctly. I recommend testing the cake with a skewer or toothpick to ensure that it's fully baked through.