Beer Fact Friday: Boiling

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Brewing Process - Boiling

Our 10-part overview of the brewing process continues! So far, we’ve milled the grain, combined it with hot water to extract its sugars and flavor, and separated it from the wort. Now free of solids, the liquid wort moves into the boil kettle. It’s time to turn up the heat. 

During the boiling stage, the temperature of the wort is raised until a rolling boil is achieved. The liquid is usually held at this temp for 60-90 minutes, though some strong beers might require even longer boiling times. 

During the boil, a few different things are happening: 

  1. High temperatures are killing bacteria and sterilizing the wort, making it fit for proper fermentation by yeast—and fit for drinking. (Fun fact: boiling wort has been part of the brewing process since well before we understood the nature of microbes in causing sickness. When clean drinking water couldn’t be found, ancient peoples were often directed to drink beer, which was known to be safe.)
  2. “Hot break” is forming. When proteins and enzymes reach a certain temperature, they solidify and form materials that clump together and fall to the bottom of the kettle after the boil. Removing the hot break improves a beer’s clarity and can help prolong shelf life. 
  3. Alpha acids are being isomerized. 

We’ll go into that last one more in-depth, because it takes a little explaining. Hops contain compounds called alpha acids, which are the main contributor to beer bitterness. But for alpha acids to add any bitterness to beer, they need to “isomerize,” undergoing a chemical process that literally changes their molecular structure. Isomerization can only occur at high heat, which means it can only occur during the boil.  

However! Hops *also* contain aromatic oils that are driven away by heat. Brewers will often stagger hop additions, balancing those added at the beginning of the boil purely for bitterness with those added toward the end of the boil purely for aroma and flavor. 

After the boiling stage is complete, the liquid wort once again needs to be separated from any solids (such as hops) that were added. This is carried out in the next step of the brewing process: the Whirlpool. We’ll cover that one next week.

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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