pintakäymisellä

Pintakäymisellä, often translated as surface fermentation, is a type of fermentation process used in the production of certain alcoholic beverages, most notably ales and some types of mead. It is characterized by the yeast's behavior during fermentation.

In pintakäymisellä, the yeast strains used, typically Saccharomyces cerevisiae, are top-fermenting yeasts. These yeasts are less tolerant of alcohol and higher temperatures compared to bottom-fermenting yeasts. As they consume sugars and produce alcohol and carbon dioxide, they tend to rise to the surface of the fermenting liquid, forming a thick, frothy head. This occurs because the yeast cells produce more carbon dioxide relative to their biomass, and the resulting bubbles attach to the yeast cells, causing them to become buoyant.

The fermentation temperature for pintakäymisellä is generally warmer than for bottom fermentation, typically ranging from 15 to 24 degrees Celsius (60 to 75 degrees Fahrenheit). This higher temperature contributes to the production of a wider range of esters and phenols by the yeast, which can impart fruity and spicy flavor notes to the final product. Ales brewed using this method are known for their complex flavor profiles.

After fermentation is complete, the yeast sediment typically remains suspended or lightly settled, rather than forming a distinct layer at the bottom as seen in bottom fermentation. This distinction is a key characteristic that differentiates surface fermentation from other fermentation methods.