When consumers reach out for a craft beer, they have an expectation of how that beer should taste. When an off flavor sneaks in, it can lose the brewery customers and hurt their reputation. Keeping off-flavors out of beer is not as difficult as it may seem, as long as brewers have the tools and know-how to do so.
An off flavor is a defect in beer that does not adhere to the style or ruins its taste. Some of the most common are diacetyl, which takes the form of butter or theater popcorn; oxidation, which comes across as papery; dimethyl sulfide, a sweet corn taste; and acetaldehyde, often taking the shape of green apples.
Causes
Many different factors cause off flavors, but it often boils down to the same basic concept: a fault in the brewing process.
Raw ingredients
To make good beer, you have to start with good raw ingredients. Malt, hops and yeast should be stored correctly; monitored for defects, mold, and pests; and used as fresh as possible. However, it all begins at the source. Brewers should know what to look out for when buying raw ingredients, starting with the vendor.
“[When it comes to] raw ingredients, you have to see who you’re buying it from. Are they reputable suppliers? We buy a lot of malt from the Czech Republic, I’ve been over their twice visiting the malt house and the hop house. One important thing for the brewers is to be auditing their vendors, making sure they know you’re watching, put a face to who they’re shipping ingredients to,” said Scott Hovey, owner and brewmaster at Adelbert’s Brewing in Austin, Texas.
If an ingredient isn’t good on its own, it won’t be good in the beer, so don’t be afraid of sensory analysis, Hovey said. “It’s like going to the supermarket. You should smell it, look at it, check the taste, the flavor. Every bag of malt, I usually pop a couple of grains in my mouth just to see what it tastes like, what it feels like. It’s surveying the quality of the ingredients.”
Water should be free from chlorine, taste fresh, and be clear.
“With water, smelling it and tasting it is as easy and effective as any test. You can have the best yeast, and the best malt, and go through the process, but if your water has chlorine in it, that can ruin the beer,” said Jim Matt, Chief Scientific Officer at Rhinegeist in Cincinnati.
Cory Hebert, brewer at Adelbert’s, agrees. “If you can’t drink your water because it’s so chlorinated, or any number of factors, then it’s definitely not going to be good to brew with. If you brew with chlorinated water, then you’ll get what’s called chlorophenol in the final beer which will leave the beer tasting like you’re drinking a plastic bag or bucket,” he said.
Fermentation
The most common time for off flavors to develop during brewing is fermentation. The reason for this typically comes down to problems with yeast.
“An overwhelming number of off flavors can be created during fermentation,” said Matt. “A lot of the time, people don’t pitch enough yeast, or they pitch too much yeast, and they’ll get off flavors. If the yeast is contaminated with something else, you can definitely get off flavors from it. That’s where you need to use the greatest amount of care. Yeast needs to be handled in an aseptic environment, so we want to make sure that we handle that yeast free from any other contamination.”
The good news is that, often, when yeast is the problem, it’s also the solution. Keeping beer on yeast a little longer, whether in the tank or through a second fermentation in the bottle, will get off flavors like diacetyl out of the end product.
“I’d say that a good 30 to 40 percent of the bad flavors I’ve tasted in beers are just the beer was rushed through the process. They just didn’t give the yeast long enough to work on, or didn’t let it settle long enough. Time would have fixed it,” said Hovey.
Cleaning, Sanitation and Maintenance
As the old saying goes, brewing is 90 percent cleaning, and one of the reasons for that is to keep the beer as clean as possible.
“The number one prerequisite to being a brewer is an obsession about cleaning. It’s true. You’ve got to keep your plant clean,” said Phil Leinhart, Brewmaster and Brewery Operations Manager at Brewery Ommegang in Cooperstown, New York.
Rhinegeist’s Matt agrees and recommends using tools to ensure tanks are thoroughly wiped of contaminants. “Cleaning and sanitation is everything. If a tank is not clean, then by definition it’s not sanitary, so there are several different ways to determine the cleanliness of a tank. My favorite way is a thorough visual inspection, and that’s usually sufficient. We have a device here called an ATP meter. ATP (Adenosine triphosphate) is a compound contained within all living organisms. The brewers will swab a tank looking for ATP, and, if its in there, then the tank is not clean,” he said.
At Rhinegeist they use Peroxyacetic acid to keep their tanks clean, while the crew at Adelbert’s has been known to use a pH swing to purge their brewing vessels.
“Something we do here is cleaning with a high alkaline, and also highly acidic solutions, so we get what you call the pH swing. You use a caustic soda, so you have a very high pH, and then you follow it with acid, so you have very low pH, so then you’re killing pretty much any organic or inorganic compound that would be present,” said Hebert.
Proper, continuous maintenance will keep equipment running well while also ensuring that it won’t harm the beer.
“If your pump is sucking in air because the mechanical seal is bad, it’s gonna cause high oxygen in your beer and your beer is gonna go stale, it becomes oxidized. It’s all related. If you let your equipment get into disrepair, it’s going to affect the product at some point. If refrigerators and cooling aren’t cold enough, you don’t take control of your fermentation temperatures efficiently, and you can’t cool the beer as quickly. It can all eventually affect your beer,” said Ommegang’s Leinhart.
Detecting Off Flavors
There are a multitude of ways to test for off flavors. Breweries equipped with or who employ labs can “plate” samples of beer to test for organisms that may cause the brew to taste off.
“Plating is [taking] a sample of beer from a tank and putting it on a media where microorganisms are encouraged to grow. Then we put that in an incubator, and we allow things to grow. If we see something growing that shouldn’t be, then we know something’s not right. Plating is a fairly inexpensive, not terribly time consuming, and fairly easy process to do that every brewery, in my opinion, should be doing. It’s pretty easy, and it doesn’t require a lot of technical skill,” said Matt.
More sophisticated technologies can also be implemented by brewery labs, such as a GeneDisc or a headspace gas chromatograph. These technologies require a higher level of skill to use and tend to cost more than many small breweries can afford. However, they aren’t always necessary when testing for off flavors. Nothing beats a good old fashion taste test.
“The analytical capabilities of a brewery can never compensate for the sensory tests that are required in your own sensory taste pallet. The reality is that you can’t go into a laboratory and get a complete understanding of the quality or the consistency of the beer just analytically,” said Christian Riemerschmid Von der Heide, President and CEO of Siebel Institute, the oldest brewery science institution in the United States.
Brewers will typically form a taste panel filled with brewers, servers and salespeople who have been trained to detect and identify specific flavors. Taste panels are used to help determine if an in-process or finished beer has any defects.
Siebel Institute, founded in 1872, offers flavor training kits for this purpose. Brewers can order from over 40 flavors, both wanted and unwanted, to “dose” their beers and hone the palates of their employees. The training has several purposes, most notably to find out who is particularly sensitive to certain smells and tastes, but also to make sure everyone is on the same page.
“You are not only training your people to detect, but also to identify. The difference is ‘Yeah, I can detect that there’s something different, but I cannot name it.’ We need to be able to do both so that everybody uses the same terminology; but also what is important is to know who is better at it than others. Therefore, if somebody that we know is very well trained in diacetyl and can pick it up at lower concentrations, and that person says ‘Yes, I can detect diacetyl,’ then this is the [person] that you pick [to test for it],” said Richard Dube, Director of Online Education at Siebel Institute.
“I would say sensory analysis and the taste panel is at least 50 percent of your quality control. So if 50 percent of your quality control isn’t standardized, using sensory kits, using flavor standards, then it becomes very subjective, and you have a vulnerability,” said Riemerschmid Von der Heide.
Using taste panels is highly recommended by Siebel, which offers on-site classes at their Chicago campus as well as an online curriculum. However, it’s wise to train all employees from the brewmaster to the newest salesperson in case a flavor problem comes about after the beer has reached consumers.
“Outside the plant, not only the brewers but also your sales force needs to be able to respond to a complaint at a bar or wherever that they say, ‘Your beer tastes funny.’ Because they have been trained to identify oxidation or diacetyl or other off flavors, they can pinpoint a little what the problem might be, or further educate the retailer and explain that it is actually part of the flavor profile of this specific beer,” said Dube.
Can off flavors be corrected?
Many off flavors can be corrected once they’re detected. For most, such as diacetyl, acetaldehyde, or sulfuric compound, a few extra days on yeast does the trick. When making certain beers, according to Adelbert’s Hebert, the process may be sped up, if done correctly.
“Many times too, especially back to diacetyl, in lagers and even English Ales, if you’re fermenting at say 68 F, you’ll do what’s called a diacetyl rest. You bring the beer up to 72 F towards the tail end of fermentation to force that yeast to clean up those off flavors and make sure everything gets scrubbed and is nice and neat and ready to drink,” said Hebert.
An unintended sour may work well blended into another beer in the brewery’s sour program. Even in the case of non-sour off flavors, the beer may be successful in a blend.
“When something is not within spec you can rebrand it as something else if the off flavor isn’t too bad. You can blend it. Sometimes we’ll take something that’s just not true to spec, and we’ll take it down in our sour program. Sometimes the secondary organisms can clean up those off flavors,” said Matt.
However, sometimes off flavors are impossible to correct. Butyric acid, often described as “baby sick;” medicinal flavors and hydrogen sulfide (rotten eggs) are examples of off flavors that cannot be corrected, and the batch will be “dumped.” When dumping becomes inevitable, which according to Matt is not that common, don’t let it become a sore point.
“There are times you have to swallow your pride and maybe take a little bit of a hit to keep quality up. Nobody likes dumping beer, but I’d rather dump a batch of beer that is not true to brand than sell it and be subpar and get a bunch of complaints from your customers,” said Matt.
Keeping off flavors out of beer doesn’t have to be complicated. According to our experts, with knowledge, foresight and a little elbow grease, brewers can substantially decrease their chances of bad tasting beer.
“It’s a multi-disciplinary approach. Just knowing your process and knowing where you’re at risk and then controlling those risks. Be knowledgeable of defects and how they’re caused, control your process, especially those critical quality control points, and then test both in the lab and with a taste panel so that you know that you’re okay,” said Leinhart.
“Pay attention to your customers and do the absolute best you can cleaning, sanitizing and using the best ingredients possible. Don’t compromise. The cheapest test that you can do is sensory. Taste everything. Let that guide you to making a quality product.”
“Just keep your brewhouse clean, make sure your ingredients are fresh, keep your yeast happy, and know your process, and you should be 95 percent of the way there,” said Hebert.