Off-flavors. We’ve all had them. Come on. I know you’ve had them. It’s nothing to be ashamed of. Well, maybe a little.

Knowing about off-flavors is really, really important for homebrewers though. Here’s why:

  • It can help you diagnose where / why things went wrong in your brew
  • It will make you a better judge of beer
  • It will help you brew more drinkable, award-winning beer
  • It will make you more attractive and sexy
Okay, so maybe not that last one.
I’d add another, non-homebrewing, reason to know your off-flavors, though: Beer education.
With more and more craft beer flooding the market, it behooves craft beer lovers to develop their palates (I’ve written about this one in another post as well). Good craft beers and the brewers who make them should be rewarded with improved sales.
Bad beer should be punished with decreased sales and probably a good old slap across the face. Knowing off flavors helps you do that–good one! Oh, and please don’t buy the malarkey of “It’s craft beer, so it’s supposed to taste like your granny’s armpit.” No. It’s not.
In this first of two posts, I’ll discuss the most common off-flavors homebrewers (and craft lovers) are likely to encounter. Here we go!

Off-Flavor #1: Diacetyl

Butter. Yummy. Maybe not in beer though..
Think butterscotch. Buttered toast. Heavy, sugary butter. If your beer smells and tastes like any of these, its probably got an unhealthy dose of Diacetyl. This bad-boy is a by-product of normal fermentation as well as, in certain instances, bacterial infection.
Diacetyl can be a desirable flavor in some styles of ales and stouts, especially those produced in the English style. But too much Diacetyl in even these beers would be considered a flaw. Which is bad.

How to stop it

Since Diacetyl forms during fermentation, you’ve got to look into that phase of the brewing process to prevent it. The thing about Diacetyl is that it forms naturally when yeast ferments wort, but is then scrubbed out again later, if you’ve ensured the following:

  • Healthy yeast growth: For yeast to remove Diacetyl, you’ve got to make sure that these wonderful little beings are happy. That means you’ve got to make sure you’ve pitched enough yeast, that you’ve aerated your wort before pitching, and that you haven’t killed your yeast by pitching it into too hot or too cold wort. Got that? Also:
  • Don’t ferment too hot: Controlling fermentation temperatures is a vital component of brewing really good beer. Keep your fermentation temp steady during primary fermentation. For ales, try aim for 16-18 degrees Celsius. For lagers, around 12-15 degrees Celsius should do it.
  • Do a Diacetyl rest: Pro brewers who want to prevent Diacetyl in their beers tend to do a Diacetyl rest around Day 5 and 6 of fermentation. It’s pretty simple: raise the temperature of your fermentation by a couple of degrees, around 18-20 degrees Celcius. Keep it there for a day or two.
    What’s happening here is the heat re-activates dormant yeast cells and encourages them to absorb Diacetyl. After the rest, you can do your normal cold conditioning at lower temperatures.
  • Keep things clean: Diacetyl can also be produced by various bacteria. Damn those bastards. So do make sure to keep things clean, especially once your wort has been chilled and you’re ready to add yeast. Go take a look at my post on sanitation to refresh your memory. It’s good for you. Promise.

Off-Flavor #2: Phenolic

Cloves. A little goes a long way.
Think cloves, medicinal, and at high concentrations, that weird Band-Aid smell. No, not Bob Geldof–the bandages, smart-ass.
Phenolic compounds can form throughout the brewing cycle and by a variety of culprits, so figuring out what went wrong can be more difficult.
Like Diacetyl, Phenols can be desirable in certain beers. Yeasts used to produce Wheat beers, Witbiers, Saissons, and most Belgian styles all have a touch of the phenolic in them.
When controlled, it should add a nice flavor of cloves and spice to the beer. But just a touch, mind you.
If your beer smells like a MASH surgery, it’s not okay. Here’s what you do:

How to stop it

  • Check your water: High levels of Chlorine compounds (chloramine) in your brewing water can cause very phenolic, medicinal off-flavors. Use a Chlorine filter or boil your water before use.
  • Don’t use bleach: Given how many high-quality, built-for-purpose sanitizers there are nowadays for homebrewers, using bleach just because it’s cheap is insane. What are you, the Grinch? Avoid bleach, because its residue can cause off-flavors in your beer. Okay?
  • Keep things clean: Yep, you guessed it. Proper sanitation, especially post-wort cooling, can go a long way in preventing most bacteria from spoiling your beer. Phenolic off-flavors are often produced by wild yeast strains and bacteria. So keep it clean, folks.
  • Bottle carefully: Wild yeast infections like phenolic compounds like creeping in during the botling phase of brewing. So remember to keep things extra-special clean and sanitary during bottling.
  • Mash temperatures: Less common, but worth checking, is phenolic compound formation due to low mash temperatures. If you’re brewing all-grain, check if your mash temperatures aren’t a bit low (45-55 degrees C). That can contribute to the formation of phenolic precursors in your wort.

Off-Flavor #3: DMS

Tomato beer anybody? No.
Think creamed corn, tomato stew, cooked vegetables. None of these tastes or aromas belong in beer. They’re always bad. Always.
DMS, or as it’s mom refers to it, Dimethyl Sulfide, resides, like a viper in the grass, inside of most malts. Once you heat up malts during mashing and boiling, DMS starts to form. Bummer.

How to stop it

  • Wort time: Unlike Hammer-time, you should try to collect your wort from mashing at a reasonable pace without letting it sit around for too long.If you’re using Brew-In-A-Bag (BIAB), that’s usually not a problem. But for brewers who use converted coolers, it can be. So collect wort slowly, but not at a pace that will allow you to read War and Peace in one sitting.
  • Full Boil: Make sure that you achieve a full, rolling, boil. I’ve spoken about this in previous posts, so go check it out. DMS is blown off by vigorous boils, so get rid of those suckers! Also, don’t cover your kettle during the boil. Allow DMS to escape. It wants to be free.
  • Limit chill time: I’m talking about Netflix and chill here. Just kidding. Chill down your boiled wort as quickly as you can afford to. Use a wort chiller. Use prayer. Whatever it takes, just make it quick, okay?
  • Good, strong fermentation: A vigorous fermentation can really help to scrub out DMS through the CO2 that naturally forms during this phase of brewing. Make sure you’ve pitched good, healthy yeast, aerate your wort, and pitched the yeast at the right temperature. If you’re brewing a high gravity beer, make sure to use yeast nutrients in the boil to help things along.
Next time, I’ll cover some more off-flavors. Now go brew some better beer.
Picture Credits: 
Butter by Taryn (CC BY 2.0)
Cloves by anuandraj (CC BY 2.0)
Tomato by photon_de (CC BY 2.0)