We speak of top fermentation when this takes place at a temperature between 18 and 32°C (64,4°F and 89,6°F). During fermentation, the yeast rises to the surface of the fermented beer. Most special beers, including Chimay, are of the "top fermentation type".
The process used in the production of ales, using yeasts which rise to the top of the fermentation tank, to be skimmed off when fermentation is complete. Fermentation temperatures are higher than for bottom fermented beers, at between 15 degrees C and 25 degrees C.