Ale yeast strains are best used at temperatures typically ranging from 50 to 77°F (10 to 25°C), though some strains will not actively ferment below 53°F (12°C). Ale yeasts are generally regarded as top-fermenting yeasts since they rise to the surface during fermentation, creating a very thick, rich yeast head. That is why the term "top-fermenting" is associated with ale yeasts. Fermentation by ale yeasts at these relatively warmer temperatures produces a beer high in esters, which many regard as a distinctive character of ale beers.