Beer Fact Friday: Lautering

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Welcome back to our multi-week overview of each step of the brewing process, from grain to glass. If you’ve haven’t been following along the past few weeks, here’s a quick refresher: In the Milling stage, we opened the malt. In the Mashing stage, we combined the malt with hot water to extract its sugars, proteins, and other compounds. In the third brewing stage we cover today, the mashing is done, and we need to separate the spent grain from the sugary liquid we’ve created, which is known as “wort.” We do that through a process called “lautering.” 

Historically, mashing and lautering usually took place in a single vessel: a combination mash/lauter tun. But, realizing that mashing and lautering in separate vessels would be more efficient, brewers moved over time toward completing each part of the process in its own space. Most modern lauters are outfitted with slotted false bottoms; this allows the brewer to drain the liquid from below while keeping the solid malt above. They’re also usually equipped with a series of rakes and knives attached to a rotating assembly, which the brewer can raise and drop as needed.

The goal of lautering is to separate the liquid wort from the spent grain while extracting as much of the sugar still trapped in the grain as possible. The process has several stages. First, the space under the plates in the lauter tun is flooded with hot water and the entire mash is transferred from the mash tun to the lauter tun using a specially designed pump. 

After a few minutes of settling, some wort is then drawn from the bottom and returned to the top of the grain bed. This process of recirculation is usually referred to by its German name: vorlauf. During this stage, grain husks filter out large particles, reducing the turbidity of the wort.

The final step of the lautering stage is called “sparging.” This involves spraying water atop the grain bed as the wort is drawn off from below; the sparge water dissolves more solids from the spent grain, allowing the brewer to extract any remaining sugars. 

The remaining liquid is drained from the lauter tun and sent to the kettle. The grain, now of no more use to the brewer, often becomes cattle feed.

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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