Most Belgian special beers ferment during 5 to 6 days at quite a high temperature (between 18°C and 22°C). The yeast then rises to the top of the tank and forms a thick layer on the beer. Because of the rising yeast, these beers are known as ‘top fermented’ or ‘high fermented beers’. It is not the temperature that makes the yeast rise, this is due to the used type of yeast culture. The yeast culture also plays an important role in determining the beer’s aroma.