Of course, beer contains alcohol – that is a given. Most of us are also aware that yeast is responsible for producing alcohol. And the conditions we provide for our yeast friends play a significant role in determining the types of alcohols that are created. Ethanol, the primary alcohol found in beer and the substance that gives us a buzz, is well-known to most of us. Today, we will explore some of the alcohols we may encounter in beer and discuss ways to control them.
Ethanol, or ethyl alcohol, typically makes up around 4-8% of beer by volume, making it the most abundant alcohol in beer. Yeast produces ethanol through the process of fermentation, as it helps yeast gain a competitive advantage over other microorganisms due to its toxic nature. Different organisms, including yeast strains, have varying tolerances for ethanol. For example, wine yeast generally has a higher tolerance for ethanol compared to beer yeast. Humans possess enzymes, primarily in the liver, that break down ethanol into simpler compounds, which are then eliminated from our bodies through the kidneys. This allows us to consume ethanol at relatively high levels compared to many other animals, but excessive consumption can have negative health consequences.
Controlling ethanol levels may appear straightforward, but brewers often spend a significant amount of time fine-tuning this aspect. The key lies in measuring the amount of fermentable sugars at the beginning of fermentation. Achieving consistent original gravity and terminal gravity readings is crucial, but not always easy. Other factors involved include creating the right environment for yeast to consume all the fermentable sugars, using healthy yeast, and, in the case of high-alcohol beers, selecting the appropriate yeast strain.
If you are familiar with the distillation process or chemistry in general, you may have heard of methanol, also known as methyl alcohol. Methanol is highly toxic to humans and has been linked to blindness and even death in high concentrations. This is one of the main reasons distillers discard the initial runnings (known as foreshots) produced during distillation.
The good news for brewers is that methanol is not a major concern in beer. One of the primary pathways for yeast to produce methanol is through pectins, which are found in fruits but not grains. Therefore, fruit beers may contain extremely low levels of methanol, similar to wine. However, these levels are nowhere near a cause for concern. Distillers, on the other hand, need to be more cautious about methanol. It is one of the main reasons why home distillation is illegal in most countries worldwide.
Higher (Fusel) Alcohols
Many brewers have heard of fusel alcohols, or simply fusels, but their understanding is often limited. Fusel alcohols are a byproduct of the fermentation process and are considered a flaw when present in high concentrations (fusel translates to “bad liquor” in German). If your beer smells like kerosene, something went wrong. The primary causes of fusel production are attributed to yeast or fermentation conditions. Fusels are sometimes associated with hangovers, although this is still a debated matter.
There are at least 45 known fusel alcohols that can be found in beer, as they include any alcohol compound containing more than two carbon atoms. However, not all fusels are inherently bad. In fact, a small amount of fusels can contribute positively to a beer, providing it with warmth and character. Stronger beer styles such as strong ales and imperial stouts are known for their pronounced fusel characteristics, which can range from ripe fruit to floral notes.
When it comes to controlling fusel alcohol production, most brewers focus on fermentation temperature. It is important to note that the pathway for fusel alcohol production is most active during the early stages of fermentation, especially during yeast growth. If you prefer to pitch yeast into warm wort to minimize lag time, ensure that the wort reaches the preferred fermentation range within 12 hours or less after pitching the yeast. After this period, fusel production can become more significant. Towards the end of fermentation, fusel production diminishes significantly, so brewers are often advised to raise the temperature slightly to ensure the yeast completes fermentation strongly, with minimal concerns regarding fusels.
Excessive use of yeast nutrients, particularly nitrogen, has also been linked to higher fusel production. Therefore, it is important to follow recommended dosage guidelines for nutrient additions. Additionally, the presence of trub (sediment) can contribute to higher levels of fusels. If possible, consider removing or racking off the trub before fermentation to produce beers with lower fusel content. Lastly, keep in mind that the temperature inside an actively fermenting vessel may be several degrees warmer than the ambient air temperature, particularly if the room temperature is set at 70 °F (21 °C).