Traditional lager bottom fermentation

The distinctions between the yeast used in ale and lager brewing are small. Traditionally, ale yeast were regarded as top fermenters that formed a frothy yeast head on the surface of the fermenting beer, which was skimmed off to be used for subsequent brews, while lager yeasts were bottom fermenters that formed little surface head and were recovered from the bottom of the fermenter (Briggs et al., 2004). Today, this is a less useful distinction as many types of ale yeast now have the capacity to fall out of solution and settle at the bottom of the fermenter (Adams Moss, 2008). 

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