When cake flour is added to angel food cake, it should be folded in by hand so the _______ do not break down.

• A. Gluten Strands
• B. Air Pockets
• C. Air Cells
• D. Foam Bubbles

Answer: (C)

Preserving the delicate air-filled structure created by beaten egg whites is the key idea. When you fold the flour in by hand, you minimize the mechanical work that can rupture the thin membranes around the air, so the air cells stay intact. If those membranes break, the air leaks out and the cake collapses or becomes dense, losing its light, airy texture.

Air cells are the tiny pockets of air inside the egg-white foam, the exact spaces you want to keep intact. Air pockets and foam bubbles describe the same concept more loosely, but air cells specifically refer to those defined air-filled spaces in the foam. Gluten strands aren’t the focus here because angel food cake relies on keeping the foam stable rather than developing gluten, and that extra mixing would risk deflating the batter.