Detecting and Fixing Off-Flavours

As you learn to brew craft beer, you want to quickly become acquainted with potential off-flavours. In a perfect world, every single batch you make would be flawless. Chances are, however, you’ll eventually make a mistake. We’ve all had a bad batch of beer from time to time. It happens. Of course, there’s a difference between a beer that underwhelms and one that offends. Usually, you’ll know right away if your beer is off. Trust your taste buds and your gut. But, sometimes, it helps to confirm your suspicions. If you’ve landed here because you’re afraid your beer might be off and you can’t pin-point the taste, I’m here to help. Let’s look at all the possible off-flavours you could come across. I suggest you bookmark this page for future reference. You never know when it’ll come in handy.

First, you need a consistent brewing process

To make that not-so-great beer a killer brew, you’re going to need to ensure that your brewing process is consistent from one batch to the next. You need to minimize all controllable variables. You’re better off brewing two or three bad batches in a row, using the exact same process, than brewing the odd great beer with a process that differs from one brew day to the next.

So, above else, ensure your process is consistent:

1. The exact same kettle
2. The exact same brewing method (BIAB, in our case)
3. The exact same water source or water treatment
4. The exact same grain mill setting
5. The exact same heat source
6. Adherence to all the basic steps of brew day and bottling. (add checklist links)

Then you can diagnose the problem

With a consistent brewing process in place, we can tackle the first step of troubleshooting our beer: determining where the off-flavour came from. This can be daunting, especially when you’re just get started with this awesome hobby.

Don’t make the mistake I did for the better part of my first two years of brewing and assume that all off-flavours are a result of bad sanitization. There are several factors that can contribute to off-flavours, and it’s a big mistake to always assume that your mistake was contamination. You could have stale ingredients. Or your fermentation temperature is too high. Or you have oxidation issues on bottling day. The only way to determine where off-flavours come from is to know where your liabilities are in your brewing process.

When you think you know the problem, you can start to tackle it. You can identify what part of the process cause the off-flavour. Once you’ve done so, you want to make the smallest possible change to the process that you think will solve the problem. And only change that one thing. If you change more than one variable, you won’t know what contributed to the improvement.

Of course, to do this, we need to learn to diagnose off-flavours. So, let’s take some time to talk about the most common off-flavours, and how we can fix them.

Common Off-flavours and how you can fix them

Alcoholic

Believe it or not, there’s such a thing as an alcoholic off-flavour. Obviously, we need alcohol in our beer, especially stronger varieties like imperial stouts and barleywine. But beers that are intended to have moderate alcohol levels can come off too boozy if the fermentation goes wonky.  To understand the problem, however, we need to understand what kind of alcohol we want, and those we don’t. The alcohol we want in our beer is ethanol, which is what yeasts puts out when converting our wort’s sugars. But sometimes, other alcohols want to join the action, primarily:

• Propanol
• Isobutanol
• Butanol
• Isoamyl alcohol

These are known as fusel alcohols. The truth is, you’ll find these alcohols—to some extent—in pretty much every brew. Most of the time, their quantities are so insignificant that we don’t detect them. But because our taste buds are so amazing, even the smallest amount can spoil the fun for us. If you find your beer tastes a bit like paint thinner or nail polish, you’ve got alcoholic off-flavours. What caused this? Most likely fermentation at too-warm a temperature. Take any and all measures possible to keep fermentation at the recommended temperature for your recipe’s yeast strain. And if you can, aim for your carboy’s surface temperature to be a bit lower than the recommended temperature, as the middle of the wort can be 10°F (6°C) higher in temperature.

Metallic

Unless you love the taste of metal in your mouth, there is pretty much no beer style on the planet that should taste of metal. If the beer tastes like you bit your cheek, or you just licked a frozen pipe in the schoolyard, you’re unlikely to enjoy it. (And for some of us, it might bring back traumatizing childhood memories!). So, how did this off-flavour creep into your beer? You won’t be shocked to hear it likely came from—you guessed it!—metal.  In the brewing world, they call this “metal contamination.”

The best way to guard against it is to use stainless steel components. If you’re going to make that kind of investment, however, take good care of your gear. Don’t use  a steel brush to clean stainless steel components and do not ever let them come in contact with bleach.

If you’re on a tighter budget, aluminum will do the trick, but you may want to avoid the guesswork and season the pot by boiling water in it for half an hour.

If you’re on an unfiltered well, your water could contain unwelcome metals. If that’s your case, save yourself the hassle and use bottled water.

Surprisingly, there could also be another suspect causing this off-flavour: malt. Specifically, improperly stored malt. You’re best bet is to find a good supplier, and brew soon after you get the malt. Don’t let it sit on your shelf for too long. And when you’re storing your malt, make sure it has a cool and dry home.

Diacetyl

Beer and popcorn can be a perfect combination, so long as they are kept separate. If your beer tastes like popcorn, however, I’m afraid to say, it’s likely off. Diacetyl—which is a common off-flavour— is the culprit. Unfortunately, it’s produced in all fermentations by all yeast strains. As with most things in life, it’s when you get too much of a good thing that things go bad.

Diacetyl is produced early in the fermentation process and is caused by initial fermentation that is way too high in temperature. If the temperature is too high in the initial fermentation, yeast over-produce diacetyl and can’t absorb it in time. In a normal fermentation, with temperatures under control, the yeast will absorb the diacetyl by the time fermentation is complete.t can also be caused by malolactic fermentation, where malic acid converts to lactic acid before converting to diacetyl.

Diacetyl can also be caused by malolactic fermentation, where malic acid converts to lactic acid before converting to diacetyl.

To be clear, in some beers, a small amount of detectable diacetyl is a good thing (British ales, for instance). If you want to keep brewing beer instead of buttery Chardonnay, here’s what you need to monitor during fermentation:

• You may want to consider incorporating a diacetyl rest in your fermentation process. In the last three or four days of fermentation, increase the temperature by 3-4 degrees F). This encourages the yeast to do a final clean-up and absorb any last traces of diacetyl.
• Be patient with primary fermentation. You’ll notice that all my recipes have a primary fermentation of 14 days. One of the reasons for this is that yeast plays an important role in ridding your beer of excess diacetyl. But it needs a bit of time to do it’s job—about a week after it hits final gravity.
• Pay closer attention to sanitization. Bacteria can also cause this off-flavour. If the first two tips above don’t apply in your case, you likely had a sanitization issue.
• Store your bottles in a cool area. Over time, if your beer is stored at a warm temperature, it can result in higher levels of diacetyl.

Estery

This one’s a bit tricky. It’s not automatically an off-flavour. It really depends on the beer style. It’s considered a critical component in some beers, and a flaw in others. Esters are created during fermentation and taste of bananas, pears, anise, or even rose petals or bubblegum.  It adds a fruity taste to the beer. It’s the kind of flavour you want in a Hefeweizen, or in many English ales (to a lesser extent), and Belgian ales, but not in a Pilsner or an American IPA. If you find yourself with a beer that shouldn’t have this flavour, you have some options for the next batch:

• Ferment at a lower temperature. The higher the temperature, the greater your chances of producing a beer high in ester (or diacetyl, as above).
• Make sure you’re pitching enough yeast and aerate your wort. If you don’t add enough oxygen, you’re on your way to an estery beer.
• If you used an English Ale yeast strain, try an American one instead.

However, unlike many off-flavours on this list, I’d argue that this one is not the end-of-the-world. Things could be worse.

Oxidized

The one time you want oxygen is when you’re pitching the yeast. After initial fermentation (about 3 days), oxygen becomes an enemy.  Oxygen lends beer a stale flavour profile. And that’s because oxygen degrades alcohol and aroma.

This off-flavour is often described as wet cardboard, or stale. Sometimes it’s also described as a sherry-like taste, but that doesn’t sound as bad to me. Granted, most of the time, that’s not the flavour you’re going for, so it’s considered an off-flavour.

Once primary fermentation is complete, avoid oxygen as much as you possibly can. But don’t stress over it. It’s nearly impossible to make home brew without introducing even a small amount of oxygen. Try, as best as you can, to avoid splashing the wort when you’re transferring it from the fermenter into the bottling bucket, and then again when you transfer it from the bottling bucket to your bottles. Never dump your beer from one vessel or another—always rack (siphon) it.

Off-flavour: Yeasty

As with alcohol, sometimes too much of a good thing can make your beer less desirable than you intended. Some beers should taste yeasty. But if you’re making a pale ale, it’s probably not a flavour you want in your beer. If your beer tastes of vegemite, you may have been too aggressive when pouring the beer out of the bottle. Remember to pour gently to leave the yeast behind. And if that wasn’t the reason for the off-flavour, you may have bottled your beer before fermentation had a chance to finish its work. If so, the yeast would have remained suspended in your wort. Of course, the opposite is true. If you leave your beer in the fermenter, sitting on top of the yeast cake (the sediment),  your beer could fall victim to autolysis, in which yeast cells self-digest. All my recipes use a single-stage, 14-day fermentation cycle, do you should have no problems of this kind. but if you leave you beer in the primary fermenter for months, you may have a problem.

Vegetal

This one offends me much less than some of the other off-flavours on this list. If you didn’t toss vegetables into the boil or the fermenter, but you find your beer tastes a bit like veggies, there could be a number of reasons for this. If you’re brewing a beer heavy on Pilsner malts, it may be vulnerable to Dimethyl sulfide (DMS), what some have described as canned corn, or cabbage, celery, or even onions. DMS happens during the malting process and if your recipe has a large proportion of Pilsner malt, extend the boil to 90 minutes instead of the usual 60.

If Pilsner malts weren’t the culprit in your beer, it’s possible that hops are causing you grief. Certain varieties of hops (Hallertauer, Herbrucker or Summit) can remind some people of garlic, green onions, grass, or hay. If that’s not your thing, try a different variety next time.

If you got all fancy on us and dry hopped your beer, this too could have played a role. Most pros will dry-hop for no more than one week. As with some of the other flavours on this list, too much of a good thing can result in bad beer. Don’t dry-hop your beer for four weeks, you may come to regret it.

Grassy

If your beer tastes like the smell of a freshly-cut lawn, you may have a grassy beer. Again, as with other off-flavours on this list, sometimes that’s not necessarily a bad thing. Certain hop varieties (Mosaic, Fuggle, and Boadicea ) are naturally grassy, especially if used late in the boil or in dry hopping.  If you didn’t use those varieties, it’s possible that too many hops matter made it into your beer. Normally you filter out the bulk of the hops matter when you transfer the wort from the kettle to the fermenter, but if your strainer isn’t doing the trick, you may need to consider racking your beer from the kettle to the carboy next time. If that sounds like too much work, try a different hop variety with a higher alpha acid. This will let you brew with a smaller quantity of hops, while still hitting your bitterness target.

As with the vegetal off-flavour, if you dry-hopped your beer, this too could have played a role. Most pros will dry-hop for no more than one week.

Solvent

This off-flavour is a version of the first one on the list (alcoholic) and the fourth (estery) and can be caused by the same problem: high fermentation temperatures. When fermentation is too high, yeasts create more esters. Unfortunately, you can find (different!) esters in nail polish remover, paint thinner, and super glue, among other products. In my early days of brewing, I used to pitch my yeast as soon as it hit the high-end of the yeast’s ideal temperature range. As I would eventually learn, this creates a problem. Your wort will warm up as it ferments, especially in the first couple days. And if that happens, you’re pretty much guaranteed to have off-flavours. You’re better off pitching the yeast at the low-end of the temperature range, to give yourself room to let the wort warm up without exceeding the ideal temperature range. If temperature control wasn’t your problem, it’s possible your beer was oxidized.

Tannic

Actually, the technical term for this off flavour is “astringency,” but most of us who have had a young red wine would know this as a tannic flavour — when you get that urge to pucker up while leaving your mouth feeling dry. I discovered this flavour once when I misread the temperature for the mash. I had it way too hot which extracted tannins from the grains. You don’t want the temperature to exceed 168-170°F (76°C) during the mash.

Off-flavour: Musty

If you enjoy the taste of a musty library, you might be better off finding a peaty scotch. In beer, musty flavours will come across smelling of decomposing yard waste, rotten wood, your grandfather’s old collection of books, or your attic. Or worse, the smell of a wet towel you left in your hockey or gym bag. Your best defence against this moldy off-flavour is good sanitization. If you’re 100% certain you properly sanitized at every possible step, you may be the victim of moldy grains.  And if you’re certain you had the freshest grain bill possible, than your beer may have been oxidized.

Aceteldehyde

Don’t ask me to pronounce this one, but acetaldehyde can be found in a variety of foods we’re all familiar with, like coffee and ripe fruit. Think tart green apples or dry cider. It’s produced by yeast in just about every beer, during primary fermentation. Normally, the yeast consumes aceteldehyde later in the fermentation, sparing us of this off-flavour. But if you didn’t have the healthiest fermentation, enough of it will survive. As with most of the off-flavours on this list, you can avoid it by making sure your properly sanitize all your gear and anything that comes into contact with your wort, especially after the boil is complete. Make sure to aerate your beer well before adding the yeast, and avoid adding oxygen at all costs once fermentation has come to an end. And don’t bottle your beer too soon. If you follow my recipes, this should not be a problem as we leave the beer to ferment for 14 days.

Sulfur

Sulfur is the technical term. We’d think of it as rotten eggs. Apparently, this is a common smell when you’re fermenting a lager, but I have only brewed ales, so I have yet to experience this phenomenon.  In this scenario, it’s completely normal. All yeast strains produce a by-product called hydrogen sulfide. Thankfully, for us ale brewers, ale fermentation is vigorous enough to stamp out this flavour. But if you brewed an ale and found it had that all-too-familiar-but-not-so-pleasant smell, you might want to consider using yeast nutrient the next time you brew—just to help ensure a vigorous fermentation.

Phenolic

Without sounding like a grade-school science teacher, phenolic compounds contain hydroxyl and carbon molecules which are responsible for many of the flavours we love in food: the spice in chile peppers, the prominent flavours of cloves, cinnamon, and nutmeg and that smoky aroma that makes so many scotches a thing of beauty. As with many of the other off-flavours on our list, sometimes, these compounds are a good thing in beer. We love the taste of clove in Hefeweizen, or the spicy notes of a farmhouse saison. Or even better, that barnyard aroma of beers made with Brettanomyces (Brett) yeast. But if this was not your intended taste profile, or if you find your beer has more of a chemical, plastic-like flavour, then you may have fallen victim to any one of the following problems:

• You have have too much chlorine in your water. Try bottled water to see if that improves things next time.
• Your yeast strain is guilty. If you’re not into this flavour, stay away from Belgian or Bavarian Weißbier yeasts and instead opt for American or British yeasts.
• Sanitization. Despite what I wrote above, it’s also possible that wild yeasts are the culprit. Pay close attention to sanitization the next time your brew. And if you’ve been using the same hoses for a while, get some new ones. I tend to buy new hoses after 10 brews, just to play it safe.

Sour/Acidic

Of course, in some beers, this is a welcome taste! But if you didn’t brew a sour beer, you may need to pay closer attention to sanitization. But if you’re not brewing a sour beer, and it comes out with a tarty aroma and flavour, perhaps bordering on the vinegar side, any number of bacteria could be responsible.  If this becomes a recurring problem, take a second look at your fermentation equipment. If you’re using plastic fermenters, consider making the switch to glass carboys. Give your plastic hoses and auto-siphon a good, long soak in the Star San (like a solid hour), just to be safe. If that fails, you’ll need new hoses and racking gear.  As I’ve said before, make it a regular habit of replacing your hoses every 1o brews.

Skunky

If you’ve ever had Stella or Heineken that was either not well stored, or on a hot summer patio, you’ll be quite familiar with this off-flavour. It smells exactly as the same suggests: like skunk. Oh, and the same can probably be said about Corona. The only difference is that the lemon wedge masks this flavour. Hmmm, maybe that’s the real reason we add lime to Corona… It really doesn’t take much to create a skunky beer. Put any beer that comes in a green or clear bottle in sunlight for a day or two, et voila, tu as Pepé le Pew.

So, one obvious preventative strategy is to only use brown bottles when bottling your home brew. Stay away from the green or clear bottles. They’re just not worth it. Beer does not take well to light, unless on a hot patio, in the shade, and consumed at a reasonably brisk pace. To play things extra safe, always store your bottles in dark corners of the house. And for those of us using glass carboys, do what I do: wrap them in a kitchen towel to protect them from any and all lights, including artificial lights in your kitchen, if you store your carboys there, as I do.  This is probably the easiest off-flavour you can avoid.