Flocculation

The way a particular yeast flocculates is often a consideration for a brewer when attempting to brew a particular style. Flocculation is the process of yeast cells coming together and dropping to the bottom of the fermentation vessel. There are three levels of flocculation that are assigned to yeast.

High Flocculators: These tend to be English or London ale strains. The yeast tends to clump after 3 to 5 days, and the ensuing yeast cake tends to be rather compact at the bottom of the fermentor. The yeast would need to be gently roused back into susmension if some of the flavors of the fermentation such as diacetyl need to be scrubbed out for whatever reason, or if additional conditioning is desired to provide better flavor balance. Highly flocculative yeasts tend to be more fruity and are great for English style ales. These yeasts flocculate well at 65 F, so there is less need to cold crash the beer is clear beer is desired.

Medium Flocculators: Lagers and American ale strains tend to fall into this category. These yeasts tend to produce cleaner beers as the yeasties stay in suspension longer, absorbing some of the flavor byproducts such as diacetyl and other fruity flavors. These yeasts also tend to be higher attenuators. Medium flocculators tend to take a little longer to clear for the homebrewer. Cold aging this type of yeast will assist in dropping the yeast out of suspension. American ales, being heavily hopped, tend to benefit from the cleaner strains allowing the hop aromas and flavors to shine through.

Low Flocculators: German Hefeweizen and Belgian Wit strains fall into this category. These styles are generally cloudy in appearance, with suspended yeast remaining in the beer for a little added flavor for the beer. Something of note: wild yeast strains tend to also fall in this category. If a beer ends up cloudy when it wasn't supposed to in addition to having some extra funky flavors, this is probably the cause.

In summary, yeast is required to be in suspention to remove unwanted flavors and increase attenuation. Lower flocculating yeasts will flocculate more quickly at lower temperatures and have less of a flavor footprint, where higher floculating yeasts will drop out of solution quickly and at higher temperatures, leaving a greater flavor footprint on the finished beer.



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