Beer Fact Friday: Filtration

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Brewing Process – Filtration

Our deep dive into each stage of the brewing process continues! Last week, we fermented our beer, allowing the yeast to digest malt sugars and produce sweet, sweet alcohol. Now it’s time to filter. 

Filtration, to get technical, is the process of removing solids from liquid by passage across or through a porous medium. In the brewery, we filter beer in a number of ways. 

One of the most common methods of filtering beer is by forcing it through diatomaceous earth. Also known as DE, diatomaceous earth is a naturally occurring substance made from the skeletal remains of microscopic algae called diatoms. The bones of these tiny critters have a unique structure composed of numerous channels and holes that can trap larger particles while allowing liquid to pass through. (DE, by the way, is the same stuff used in many pool filters.)

Diatoms,Suriella,Magnification
A diatom, the stuff from which DE is made.

A more high-tech method of filtration is through use of a centrifuge. Though these devices are very expensive and look pretty imposing, the way they operate is actually fairly simple: They spin the beer very quickly, making use of centrifugal force to remove heavy particles. When a centrifuge spins the liquid within a round chamber, the heaviest components of the liquid are pushed toward the rotation chamber’s outer wall, while the lighter components (water and alcohol, mainly) stay closer to the center axis. Once the heavier particles have been spun to the outside of the chamber, the clear, filtered beer is drained from the centrifuge, and the heavier stuff is left behind. 

With unfiltered beers like those cloudy New England IPAs becoming ever more popular, you might be wondering: Why filter beer at all? Filtration helps stabilize beer, increasing its shelf life. It can also remove elements, such as dead yeast, that could eventually make the beer unpalatable. Plus, there’s just something to be said about the beauty of a crystal-clear pint. 

Beer Fact Friday is our weekly exploration of the topics that make beer the world’s most interesting beverage. Check back here next week—or follow us on FacebookInstagram, or Twitter—for more fascinating beer trivia. 

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