Homebrew Troubleshooting: How to Fix Yeast-Derived Off-Flavors in Your Beer

Chris Cohen

As homebrewers we put many hours and not a small amount of money into making our beer. We constantly strive to improve, but in many cases our homebrew just isn't as good as the pro stuff. It has "that homebrew flavor."

It can be difficult to figure out what the heck that off flavor is and why it keeps turning up in your beer, but becoming a better brewer requires analyzing your homebrew to figure out what the issue is and changing your technique to fix it.

Those guys and gals who bring home ribbons in homebrew competitions didn't start out making perfect beer every time. They've tweaked their brewing and fermentation techniques, they're extremely careful about their sanitization practices, and they've dialed in their recipes over time, batch by batch. In many cases they received advice on how to do this from the scoresheets they receive from competitions and analysis from advanced homebrewers in a local homebrew club.

The first step to fixing your beer is to know and avoid the major off flavors so that you can focus more on the fun parts of brewing.

It's All About Yeast

You may feel proud of your homebrew, but it's worth remembering that yeast really make the beer. And many off flavors come from yeast related issues. There are a few simple things you can do to avoid the majority of these yeast-related problems.

First, pitch the proper amount of healthy active yeast. Packets and vials of homebrew yeast pitches can be old and they hardly have enough yeast in them for many beers to begin with, so making yeast starters a few days prior to brewing can make a big difference in the quality of your homebrew. Don't know how to make a yeast starter? Here's our guide.

Second, be totally anal about proper cleaning and sanitizing. Replace any old plastic equipment, and use products specifically made for homebrewing sanitation. Otherwise something other than your brewer's yeast will ferment your beer, and the results won't be pretty.

Finally, control the temperature of your fermentation to ensure your yeast don't either go dormant because they're cold or spit out all sorts of crazy flavors because they're overactive and hot.

Shall we get into specifics? Below, we'll look at a few of the most common undesirable flavors that come from brewer's yeast and other bugs. Stay tuned for a second installment on off-flavors that result from other homebrewing issues.



Diacetyl has a butterscotch flavor that in high doses tastes and smells like movie theater popcorn butter. It was quite literally the chemical used to flavor imitation butter (used less nowadays as it's been linked to lung disease in factory workers at production factories).

Diacetyl can also change a beer's texture, giving it a slick characteristic. As with all flavors and aromas, different people have different levels of sensitivity to diacetyl aroma and flavor. In many beer styles, especially lagers, diacetyl is considered an off flavor. But low levels of diacetyl are acceptable in some ales, particularly traditional British styles.

Diacetyl is one of the many chemical compounds that yeast produce as they ferment beer. If the yeast is allowed to properly complete the final stages of fermentation it will reabsorb the diacetyl and process it into flavorless compounds. It is therefore key to allow fermentation run its full course to avoid diacetyl and other off flavors. It may look like the beer isn't bubbling much after "primary fermentation," but there's still activity going on.

Homebrewers should leave ales in their initial fermentation vessel for several days after fermentation activity appears to have slowed significantly—for lagers wait a week. If the beer is racked off the yeast into a secondary fermentation vessel too early, or if the temperature drops and the yeast go dormant, then all that diacetyl will remain in the beer.

Some yeast strains, primarily British ale strains, are highly flocculant (i.e. they clump together) and they fall out of solution more quickly, therefore low levels of diacetyl are acceptable in those beers. When fermenting lagers, many brewers raise the temperature of the beer by 5-10 degrees after fermentation but prior to the lagering phase in order to get the yeast more active so they quickly and efficiently remove any remaining diacetyl from the beer. This is call a "diacetyl rest," and it works for ales, too. You need good fermentation temperature control to pull off this trick.

"So if your beer has a buttery flavor in combination with either a lactic sourness and/or gushing bottles, it's a sure bet that you need to work on your sanitation."

Diacetyl can also get into your beer if it gets infected with bacteria, especially the prolific diacetyl producers Pediococcus and Lactobacillus. Both of these bugs also produce lactic acid and can lead to a beer over-carbonating in the bottle as the bugs continue to break down sugars and produce CO2 in the bottle long after your brewer's yeast has gone dormant. So if your beer has a buttery flavor in combination with either a lactic sourness and/or gushing bottles, it's a sure bet that you need to work on your sanitation.

Clean and sanitize your gear with products such as PBW (Powdered Brewery Wash) plus Star San. I'll have more notes about sanitizing below.

Also, replace any plastic parts in your brewery. After months of use, plastic gear commonly gets microscopic scratches in them that harbor impossible to clean colonies of bacteria and wild yeast. Don't ruin the beer you put all that time and money into because you're too cheap to replace tubing and plastic buckets.

If you taste diacetyl flavors in commercial beer served to you at a bar, it's often the case that the draft lines are infected with these same bugs because the bar isn't properly cleaning their tap system. Find another bar.



Acetaldehyde tastes like freshly cut green apples. It's easy to remember this one because it's associated with "green" beers that are served to young or, as with diacetyl, beers that were removed from their yeast too early. Acetaldehyde is another compound that's always produced by brewer's yeast in the process of fermentation, however, as with diacetyl the yeast will clean it up given the opportunity to fully complete fermentation. So this is an easy fix: Just leave the beer on the yeast long enough and make sure the temperature doesn't drop causing the yeast to go dormant before they finish their job.

Alcoholic and Solventy Flavors


A touch of alcohol character in a beer can be pleasant. It provides balance to sweet malt, it has a subtle perfumy or spicy aroma, and it can warm your throat (in a nice way). This is not uncommon in beers over 6% ABV and it's almost always the case for big beers such as barleywines and doppelbocks, which often come in at over 8% ABV. It's a problem, however, if the alcoholic character of the beer is harsh or solvent-like.

Solventy fusel alcohols are those that are described as having an aroma or flavor similar to nail polish remover or even paint thinner in extreme instances. Fusel alcohols in beer can include butanol, isobutanol, propanol, and isoamyl alcohol (among others), rather than the more friendly ethanol. Beyond tasting and smelling solventy, fusel alcohols can be harsh on the tongue and throat, they can go beyond throat warming straight to being hot.

Solventy alcoholic character is typically caused by fermenting your beer at too high a temperature. Most ale yeasts like to ferment around 70°F. If your wort isn't chilled to that level before you pitch your yeast or is allowed to rise in temperature during the early phases of primary fermentation, you'll get more fusel alcohols in your beer. You definitely don't want to let an ale ferment at anywhere near 80°F unless you're making a high temp fermenting style such as a saison.

The main fix for solventy alcohol character is to chill your wort until it is down into the 60s°F before pitching your yeast, then place your fermenter in a cool closet in the center of your home where there is a constant temperature. If you live in Florida or some other hot spot, the only solution may be to put together a temp controlled fermentation chamber. There are plenty of ways to do this, but most are simply a small fridge or chest freezer connected to a temperature controller that turns on the fridge or freezer when the temp rises too high inside. This is a very simple option, but it's not exactly compact.

The vast majority of fusel alcohols in homebrew come from hot fermentation, but to complicate matters, it is possible for fusel alcohols to arise from oxidation or from leaving the beer sitting on the trub in the fermenter for a really long time. The trub (pronounced "troob") is all that funk at the bottom of the fermenter, including the coagulated hot and cold break proteins, hop particles, and dead or dormant yeast that has sunk to the bottom. This isn't an issue unless you're leaving the beer on the trub for months, so this shouldn't be an issue for most homebrewers.

Phenolic Flavors


Phenolic compounds can be an important part of the flavor and aromas of certain beers, such as the clove character that German hefeweizen yeast produces or the smokiness in Rauchbiers that comes from the smoked malt. For most beers, however, noticeable levels of phenols are not a good thing. Especially if they're the phenols that taste or smell like plastic, bandaids, or medicine.

If your beer has a not-entirely-unpleasant clove or spicy phenolic character, it's possible that you just fermented your beer at too high a temperature and can fix it by controlling your fermentation temp in the future. If your beer has a medicinal flavor and you've been using bleach to sanitize your gear, that's probably your problem, switch to something like Star San. Medicinal flavor can also come from tap water with high levels of chloramines, a common additive used to disinfect tap water. To deal with this, do a little research on using Campden tablets to remove chloramines from your brewing water.

Most likely though, these nasty flavors are an indication that your beer has been infected by wild yeast or bacteria. This arises from not cleaning and sanitizing your brewing gear properly, in particular any gear that the beer touches once it is cooled down after the boil.

Cleaning and sanitizing brewing gear is a two step process. First, you clean, second, you sanitize. You cannot sanitize something that is not clean. Dirt and grime create places for foreign microbes to hide from your sanitizer. If there is dirt on your gear, there is also bacteria and wild yeast. Use dedicated products for cleaning and sanitizing your equipment. Cleaners and sanitizers are different products that do different things, one cannot replace the other. Brewery cleaners are powerful alkali chemicals that remove inorganic material from surfaces. Sanitizers are acids that kill organic material. Using them both is a two step process.

Many homebrewers prefer cleaning with Powdered Brewery Wash (PBW) and sanitizing with foamy Star San. Always follow the directions on whatever products you chose. Keep in mind that higher than recommended concentrations of these chemicals are no more effective. If you've got some serious grime to clean, soaking gear in hot water and PBW overnight will remove practically anything, including burnt and caramelized funk on the bottom of a brew kettle or crusty yeast gunk from the side of a fermenter. Star San requires only 30 seconds of contact time to sanitize a clean surface. These are safe to use on most metals and plastics used by homebrewers.

Keep an eye on any plastic gear, which can get scratched up, creating hiding places for wild yeast and bacteria. Never clean these items with rough sponges or scratchy items. The buildup of gunk, scratches, and foreign microbes in brewing gear is one reason why many homebrewers first batch turns out to be better than their later batches. Replace plastic gear once a year.