Why does my beer taste bad? (Part 3)

Homebrewing — By DJ Spiess on August 12, 2009 at 1:53 pm

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The alcohol burn (alcoholic)

Some alcohols taste warm and there are others which taste like jet fuel. The jet fuel beers taste overly alcoholic and burn as they travel down your throat. Other unwanted alcohol flavors include strong unwanted banana flavors, chemical flavors like acetone, or overly spicy flavors. These flavors are often called the jet fuel flavors.

The off flavors are caused by propanol, butanol, isobutanol, isoamyl (the strong banana flavor) as well as several other undesired alcohols. These alcohols are known as fusel alcohols. This family of alcohols has more than two carbon atoms in the molecule, and often gives beers the taste of really poor tequila. Fusel alcohols also have an oily feel to them. One way to spot fusel alcohols is an oily layer on top of the wort during or after fermentation.

Really high levels of these fusel alcohols, as in poor quality moonshine, can cause illness, nausea, or even a coma. In homebrew, fusel alcohols are not in high enough quantity to pose a concern other than bad taste. For some styles fusel alcohols are not only acceptable, they are expected. Stronger beers such as barley wines are a good example where some fusel alcohol is desired. These flavors however should never taste like solvent.

The jet fuel flavors are usually caused by fermenting your beer at a temperature too warm for your yeast (over 80 F). In fact, this is the most common cause for fusel alcohols. When your yeast produces alcohol in warmer temperatures, they produce more fusel alcohols. The easiest way to avoid this problem is to pitch your yeast at the proper temperatures.

Other factors which can contribute to higher amounts of fusel alcohols are elevated levels of amino acids in the wort, anaerobic conditions (low oxygenated wort), continuous agitation of the wort, excessive yeast growth, or wort with an already high ethanol concentration. Fusel alcohols can also form if your beer sits on the trub too long.

These causes of fusel alcohol have the same underlying problem – stressed yeast. To avoid the alcohol burn, you need to keep your yeast happy as possible in the best wort environment as possible.

Fusel alcohols are alcohols with more than 2 carbon atoms
Jet fuel beer is usually caused by too warm temperatures or stressed yeast from low oxygenated wort
Make sure you ferment the beer within the correct temperature range
Move your beer off of the trub as soon as fermentation completes

Creamed Corn/Cooked Vegetables (DMS)

If your beer has an unwanted cooked corn flavor or worse yet, it tastes like oysters, you might have a DMS problem. DMS (dimethyl sulfides) occur in beer either naturally or from a bacterial infection.
The naturally occurring DMS comes from S-methyl methionine (SMM), a product of malt germination. SMM levels in the malt are reduced when it is roasted and never forms as DMS later in your wort. This makes DMS less of an issue in beers that use roasted malts.

DMS is more of a concern in lighter beers, especially lagers, because the lighter grains do not have the SMM removed from roasting. The levels of SMM in your malt are directly related to the levels of DMS in your wort. DMS “breaks” off from SMM during the boil of your wort.

A cooked corn flavor is usually a sign of a DMS problem

As your wort boils, DMS is produced and boiled off. It evaporates and is removed from your beer. That’s good. If you boil your wort with the lid on, the DMS will condense and fall back into the kettle. That’s bad. If you want to avoid DMS, step one is to boil your wort with the lid OFF the brew kettle.

Step two is to boil your wort for at least an hour. The longer your boil is over 158 F, the more DMS is removed from your wort. Slow cooling of your wort will also allow DMS to form, so you want to cool your wort as quickly as possible.

DMS can also form from bacterial infections. An infection can convert Dimethyl sulfoxide (DMSO) into DMS by removing the oxygen. To avoid bacterial DSM, make sure you are practicing good sanitation techniques.

Bacterial infections will cause a cooked vegetable flavor
Boil your wort for at least an hour with the lid off
Lighter beers, such as Pilsners, are more susceptible to DMS problems

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DJ Spiess

I am a avid homebrewer and winemaker. I’ve been making my own beer and wine for many years. I started making beer when I was in college (mostly because the drinking age in the United States is 21). My first few beers were horrible. The beers are much better now, and I often supply my neighborhood with free beer!

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Tags: beer, dms, homebrew, infection

zach

“If you boil your wort with the lid on, the DMS will condense and fall back into the kettle. That’s bad. If you want to avoid DMS, step one is to boil your wort with the lid OFF the brew kettle.”

Ummm, yeah. I'm gonna have to go ahead and sorta .. disagree with you.

I use a horribly under-powered gas range to boil 5 gallons of wort. As a consequence of my brew pot size and the range's thermal output, I must leave the lid partially on to keep it at a boil. I've never had an issue with DMS, but I could have just been lucky (30-some batches into my brewing life). I figure that if significant steam is escaping, the DMS is going with it. The small bit that remains in perpetual circulation under the lid doesn't seem to matter. For those of us without dedicated 100,000 BTU propane burners, keeping the lid off isn't always an option.