Definition - What does Cap Fall mean?
Cap fall is described as the time in which the wine cap sinks into the wine when the process of fermentation is complete. The wine cap includes the solids of a fermenting wine like the pulp and must that rise to the top during fermentation.
When fermentation is done, there is less carbon dioxide gas left in the wine to keep the cap afloat, and thus the cap falls.
WineFrog explains Cap Fall
When grapes are crushed for winemaking, the solids including the skins will float to the top of the juice after about 24-hours following the crushing stage. This is called the cap.
Maintenance of the cap is performed throughout fermentation by punchdowns or pump-overs in order to have an even fermentation of the wine and to avoid a stuck fermentation. When the fermentation is finished, the cap will fall into the finished wine, which tells the winemaker it is time to press the wine.