Of course beer has alcohol in it — that much is given. Most of us also know that yeast is the producer of our alcohol. And the conditions that we provide for our yeast friends will play a large role to the extent of what alcohols are created. Most of us are familiar with ethanol, the primary alcohol found in beer and the substance that gives us a buzz. Today we’ll take a spin through some of the alcohols we may encounter in our beer and ways we can control for them.
Often comprising somewhere between 4–8% of beer by volume, ethanol (or ethyl alcohol) is by far the most abundant alcohol found in beer. Through the process of fermentation, yeast produces it to gain a competitive advantage over other microorganisms since ethanol is toxic. Different organisms have different tolerances, including yeast. For example, wine yeast generally has a stronger tolerance for ethanol than beer yeast. We humans have enzymes, found mainly in our liver, that process ethanol breaking it down into simpler compounds that can be flushed from our system through our kidneys. This process allows us to consume ethanol at fairly high levels compared to many other animals, but as we well know, it can come at a health cost if we abuse it.
Ethanol levels may seem like an easy factor to control, but brewers can spend a huge amount of time trying to hone in on this detail. The key is gauging the amount of fermentable sugars at the start of fermentation. Seems simple, right? But that means hitting your original gravity and terminal gravity every time. Yeah . . . not so easy. The other factors involved include providing the right environment for yeast to consume all the fermentable sugars, using healthy yeast, and, in some cases, using the correct strain for the job (in the case of high-alcohol beer).
If you are familiar with the distillation process, or chemistry in general, then you’re probably familiar with methanol (or methyl alcohol). This is highly toxic alcohol to humans and has been linked to blindness and even death in higher concentrations. Methanol is one of the main reasons distillers will dump the first runnings (called foreshots) that come out of the distillation process.
The good news for brewers is that methanol is not really a concern in beer. One of the main pathways for yeast to produce methanol is through pectins; something found in fruit, but not grains. So fruit beer may have some extremely low levels of methanol (same with wine), but nowhere near levels of concern. Distillers, on the other hand, need to be more careful of methanol. This alcohol is one of the main reasons that home distillation is illegal in most countries in the world.
Higher (Fusel) Alcohols
A lot of brewers have heard about fusel alcohols, or just fusels, but they’re often not well understood. First off, they are a product of the fermentation process and when found in higher concentrations are a flaw (fusel translates to “bad liquor” in German). If your beer smells like kerosene, you messed up. When fusels are noted the yeast or fermentation conditions will be considered the root cause. Fusels are also commonly cited as a contributor to hangovers, but this is still a matter up for debate.
There are at least 45 known fusels to occur in beer, as they are simply any alcohol compound that has more than two carbon atoms. But all things fusels aren’t inherently bad, in fact a little fusels may be a good thing and even a happy, healthy fermentation will produce some. Fusels are known for the warming sensation on the palate found in many stronger beers like strong ales and imperial stouts. Fusels can exhibit characteristics ranging from ripe fruit to floral. At moderate levels these can work to build character, along with esters, in ales.
When it comes to controlling fusel alcohol production, most brewers look at the fermentation temperature. One of the most important things to note is that the pathway to fusel alcohol production is most active early in fermentation, during yeast growth. If you’re a brewer that likes to pitch yeast in warm wort to minimize lagtime, just be sure to get your wort down within the preferred fermentation range within 12 hours or less after yeast pitch. After that period fusel production can begin in earnest. Near the end of fermentation this pathway has all but closed as well, so brewers are often encouraged to warm their beer to make sure the yeast can finish fermentation strong, with little concern for fusels.
There are also several lesser-known reasons for higher fusel production. Excessive use of yeast nutrients, nitrogen in particular, is also tied to higher production of fusels. So be sure to keep your nutrient additions to recommended dosages. The presence of trub has been linked to higher levels of fusels as well. If you have the ability to dump the trub or rack off the trub before fermentation, you may be able to produce beers lower in fusels. Finally, if the room you’re storing your active fermenter in is set at 70 °F (21 °C), note that the temperature inside the active fermentation may be several degrees warmer. My rule of thumb is to expect temperature in an active fermenter to be about 5 °F (2.5 °C) warmer than ambient air temperature (this can get even warmer in larger fermenters).