Fusel Alcohols - how to prevent them from occurring in your homebrew beers

Friday, February 24, 2023

Three summers ago I learned a really important lesson when brewing and how temperature can affect beer. 


I was fermenting a Nut Brown Ale in my car shed. I had wrapped in plenty of old sheets. I left the beer to its own devices and forgot all about it.


A week or so later I checked in on it and the beer had a 'cooked' sense of smell. I bottled the beer and after conditioning was over, I poured my first beer. 


It tasted like methylated spirits! 


With hindsight, I realized the summer heat had made the garage as hot as a glass house. And that's when I learned how fusel alcohol can ruin the home brewing experience. 


fusel alcohols

What are Fusel Alcohols?

Fusel alcohols are a group of higher alcohols that are produced by yeast during the fermentation process. They are named after the German word "fusel," which means "bad liquor." These compounds are often responsible for the harsh, solvent-like flavors and aromas that are associated with poorly made beer.

Some of the most common fusel alcohols include:
These alcohols are typically produced in small amounts during fermentation, and they can contribute to the fruity, floral, or spicy flavors and aromas of the beer. However, if they are produced in excessive amounts, they can result in off-flavors and aromas that can ruin the taste of the beer.

How are Fusel Alcohols Produced During Beer Brewing?

Fusel alcohols are produced during the fermentation process when yeast metabolizes the sugars in the wort (the liquid extracted from the malted grains). The yeast converts the sugars into alcohol, carbon dioxide, and other compounds, including fusel alcohols.

The production of fusel alcohols is influenced by a variety of factors, including the type of yeast used, the temperature of the fermentation, the amount of oxygen present, and the composition of the wort.

How to Prevent unwanted Fusel Alcohols when Homebrewing beer?

As a homebrewer, there are several steps you can take to prevent the production of fusel alcohols and ensure a better end beer:

Use the right yeast: 

Choosing the right yeast strain is essential to preventing fusel alcohol production. Different yeast strains have different characteristics, and some are more likely to produce fusel alcohols than others. Choose a yeast strain that is known for producing clean, crisp flavors - Fermentis is a good example.

Control the fermentation temperature: 

In my experience, this is a crucial element - the temperature of the fermentation plays a significant role in the production of fusel alcohols. 

If the temperature is too high, the yeast will produce more fusel alcohols. 

Keep the fermentation temperature within the recommended range for your yeast strain. This means not exposing your fermenting drum to stuffy rooms, or direct sunlight.

Oxygenation: 

Yeast requires oxygen to grow and metabolize sugars. However, excessive oxygenation can lead to the production of fusel alcohols. 

Remember, when brewing your beer (before fermentation) it's good to aerate the wort - when I use a brewing kit and am adding the water, I make sure the wort turbulently enters to get some oxygen in. 

Conversely, dear reader, when it is time for bottling, your beer doesn't need too much oxygen - this is why some brewers like to use a bottling wand.  

Proper sanitation of brewing equipment: 

Proper sanitation is crucial to preventing the growth of bacteria that can produce fusel alcohols. Make sure all equipment is clean and sanitized before use.

Summary:

Fusel alcohols are a group of compounds that are produced during the fermentation process of beer. While they can contribute to the flavor and aroma of beer, excessive production can result in off-flavors and aromas that can ruin the taste of the beer. 

As a homebrewer, controlling the fermentation temperature, choosing the right yeast strain, and proper sanitation can help prevent the production of fusel alcohols and ensure a better end product.
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