Although a significant amount of yeast suspended in the storage tank will settle to the bottom through gravity sedimentation, it can be time-consuming to prepare beers for filtration using this method. As a result, brewers can add fining agents at the beginning or during storage to expedite the sedimentation process. Alternatively, brewers can use centrifugation to remove yeast and other solids after fermentation. The following sections describe each of these processes.
While simple sedimentation can yield satisfactory clarity, better and faster results can be achieved by using fining agents such as isinglass and gelatin.
Isinglass is a traditional clarifying agent used in the United Kingdom for “real ale,” a beer style that benefits from a 48-hour clarification before or after being casked. It is also used to fine chilled and filtered beers. Isinglass is a gelatinous substance derived from the internal membranes of fish bladders and comes in various forms. The current accepted mechanism involves direct interaction between positively charged isinglass and negatively charged yeast, resulting in the formation of flocs that precipitate. Its effectiveness in settling ale yeast varies depending on the strain of yeast, and it is generally not recommended for precipitating lager yeast.
Centrifugation is a popular method for reducing the yeast content of beer and is often used when fining agents are not employed or when used in conjunction with fining agents. Many brewers who practice accelerated cold conditioning utilize centrifuges as they provide greater control over yeast count and eliminate the time required for maturation and fining.
Centrifuge During Beer Transfer
The first method involves using a centrifuge to separate the yeast crop as the beer is transferred from the fermenter to the conditioning tanks. This achieves both beer transfer and yeast collection in a single step.
Centrifuge Following Yeast Sedimentation
The second method involves using a centrifuge to clarify the beer after the yeast has been separated through sedimentation.
Advantages and Disadvantages
Centrifuges offer several advantages, including requiring minimal space, providing consistent clarity, being self-cleaning for the most part, minimizing oxygen exposure, and allowing continuous operation indefinitely.