What Are The Chemical Reactions Involved In Beer Making?

Beer. Possibly one of the first products made intentionally by Man as early as the Neolithic period.

Some of the most ancient writings are beer recipes, a  testament to the importance of this beverage, and historians even suggest it was instrumental for the development of civilisation as we know it! This hasn’t changed in over 10,000 years and beer remains the most popular alcoholic drink around the world.

The process of beer making involves an extremely complex and delicate series of chemical reactions that must occur within specific conditions to ensure a high quality final product. The current process may have developed and improved much since its inception, but the basic principle of transforming sugar into alcohol in the presence of yeast still stands.

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The First Chemical Reactions

Simply by soaking the grains in hot water, the enzyme amylase is released and activated. This step is vital to convert starch (polysaccharide with multiple glucose molecules) into maltose (disaccharide with two glucose molecules). The simpler double-saccharides then become easy targets for the yeast during fermentation.

To give beer its characteristic bitter taste, hops (Humulus lupulus) are added during this initial phase. Beer connoisseurs will attest the importance of this stage, to generate isoalpha acid isohumulone from the original humulone. Boiling the solution also eliminates harmful bacteria, removes volatile components and precipitates protein, increasing the final product’s stability; as well as caramelises and darkens sugars – this is called a Malliard reaction and we’ve discussed it previously when looking at our Christmas turkey.


This is the key step in the entire process. If fermentation fails, there is no beer. However, this is a pretty fail-proof process as long as temperature and pressure conditions are ideal, with yeast efficiently producing the golden beverage so much appreciated by many. To put it in technical jargon, addition of Saccharomyces cerevisiae will ferment the sugars present (glucose) to produce alcohol (ethanol), in the absence of oxygen. As the reaction progresses, CO2 produced needs to be vented off the solution.

Diagram showing alcohol fermentation in yeast cells

In addition to the synthesis of ethanol, other parallel reactions originate phenols and esters, as well as chlorine and fatty acids, all contributing to the final flavour. Diacetyl is a ketone particularly relevant to darker ales, giving it a lovely and sweet butterscotch-like flavouring. Fermentation will continue as long as there is sugar available.

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The Final Product

Some recipes require the addition of a small amount of sugar to encourage any live yeast to continue fermentation after bottling, and use CO2 as natural carbonation, but once fermentation is completed, the product can be called beer. It’s the end of the journey!

Now, next time you go for a drink down your local pub, you’ll have something to talk about! Amaze your friends with your inside knowledge about the chemical reactions involved in brewing… and they may buy you a round!

Alex Reis
Alex Reis is a freelance science writer, with a particular expertise in the field of biological sciences. She has several years experience in scientific writing and research, with various scientific manuscripts published in high impact factor journals, including Nature Cell Biology, as well as articles promoted in more mainstream publications.
Alex Reis
Alex Reis
Alex Reis

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