The Collaborative International Dictionary
Top fermentation
Top fermentation \Top fermentation\ An alcoholic fermentation during which the yeast cells are carried to the top of the fermenting liquid. It proceeds with some violence and requires a temperature of 14-30[deg] C. (58-86[deg] F.). It is used in the production of ale, porter, etc., and of wines high in alcohol, and in distilling.
WordNet
top fermentation
n. a violent kind of alcoholic fermentation at a temperature high enough to carry the yeast cells to the top of the fermenting liquid; used in the production of ale; "top fermentation uses a yeast that ferments at higher temperatures than that used for bottom fermentation"