A fermentation method driven by Saccharomyces pastorianus strains operating at cool temperatures, typically between 7 and 13 degrees Celsius. Because the yeast cells flocculate and sink to the bottom of the conical fermenter as they work, the process takes longer than warm fermentation. This slow, cold metabolism produces fewer esters and fusel alcohols, resulting in the clean, crisp flavor profile characteristic of lagers.
We need to hold the bottom fermentation at 10 degrees for another week before we even think about a diacetyl rest.
Do not mix it up with
- Top fermentation: Bottom fermentation uses cold-tolerant yeast that sinks, while top fermentation uses warm-fermenting yeast that rises.
Related terms
Top fermentation
A brewing process where yeast cells rise to the surface of the liquid during active fermentation.
Unterhefe
A German term for bottom-fermenting yeast used primarily in the production of lagers.
Attenuation
The percentage of original sugars in a wort or must that yeast has converted into ethanol and carbon dioxide.