Above: Weighing the hops (Markus Raupach)

Barley, water, hops, and yeast: How do four simple ingredients come together to make thousands of different kinds of beer? The answer lies in the science of brewing. Brewing beer involves a series of complex biochemical reactions, from breaking down starches into sugars to breaking down sugars to release alcohol.

Did you know? Ultraviolet (UV) light causes a chemical reaction in hops that gives beer a skunk-like odour. Most beer is bottled in dark brown glass to prevent this from happening.

The first step in brewing is malting, which involves soaking barley in water. Barley, the seed of the barley plant, is both a grain and a source of starch. Soaking the barley allows the starches to germinate (or grow), so they become softer and easier to extract for use in the next step. Once the seeds have soaked long enough, they are dried out. This step is important because the temperature used to dry them will determine the type of malt (dark or light). Barley dried at higher temperatures produces a dark malt and lower temperatures result in a light malt. This affects both the colour and the flavour of the beer.

Adding hot water to the malted barley activates temperature-dependent enzymes. Enzymes are small proteins that exist in all organisms. They bind to other molecules and increase the speed of chemical reactions. Enzymes convert starches to sugars through a process called saccharification. After filtering off the leftover grain, the result is a sugary liquid called wort.

Next, the brewer adds hops to the boiling wort. Hops are flower buds from the hop vine. Resins within these buds give beer its bitterness and aroma. In order to extract the bitter resins from the hops, the wort must be boiled so the hops become soluble and dissolve into the wort. By playing around with the amount of hops, you can control just how bitter (or “hoppy”) the beer will be.

Finally, the brewer adds yeast. Yeast is a single-celled organism that feeds on sugar. It is added to the sweet, hoppy mixture and rapidly breaks down sugars, releasing carbon dioxide and alcohol. This is called fermentation, and it ends when the yeast has consumed almost all of the sugar. After fermentation is complete, the yeast is collected and re-used for the next batch of beer.

Did you know? Alcohol has a lower boiling point (78.3 degrees Celsius) than water (100 degrees Celsius). To make non-alcoholic beer from regular beer, you simply have to boil off the alcohol.

The end product is a hoppy, carbonated, alcoholic drink called beer. The flavour and type of beer depends on temperature, timing, and amount of each ingredient. For example, the main difference between ale and lager is the temperature at which fermentation takes place.

However, the most important ingredient is yeast, especially if the brewer wants to ensure consistent flavour. Breweries that make the same beer over and over must use the same strain of yeast. Most breweries will happily give out their recipes, since without their specific strain of yeast, you can’t replicate their beer! In fact, breweries are extremely protective of their yeast strain and often store a backup supply off-site in case of contamination. A mutation in the yeast (a change in its DNA) can create a strain of yeast so different from the original it would be like comparing two different breeds of dogs! Mutated yeast will produce a completely different (and possibly bad) tasting beer.

This devotion to maintaining a yeast strain reflects just how much scientific research goes into developing a seemingly simple beverage. Cheers to that!


A New Look at Brewing (Rensselaer Polytechnic Institute)

Brew a Great Non-Alcoholic Beer (John Naleszkieqicz, Brew Your Own: The How-To Homebrew Beer Magazine)

Brewer’s Art (Caledonian Beer)

Using multiple yeast strains (Chris White, Craft Beer Quarterly)

When Light Meets Beer (Robert L. Wolke, The Washington Post)

Yeast Fermentation and the Making of Beer and Wine (Luisa Alba-Lois and Claudia Segal-Kischinevzky, Nature Education)

Kate Williams

Kate Williams is currently working on her PhD in Neuroscience at McMaster University.  Her research focuses on how the brain changes during development and aging.  In her spare time she enjoys traveling, reading, running, and playing softball.

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