Every individual has her own palate and preferred styles and flavors of beer. But when it comes to brewing science, there are a few tastes that just don’t belong.

Akademia Brewing Company’s sous chef, Brian Johnstone, reacts to an off-flavored beer sample.

“When a beer gets really old, it starts tasting like morning breath or cardboard,” Owen Ogletree, founder of Brewtopia Events, LLC and local craft beer guru, said of the oxidized off-flavor. “It’s a common flaw. Some ways you can slow down oxidation are to drink it quicker and keep the beer cold. Cold beer oxidizes 30 percent slower than beer at room temperature. Cans oxidize slower; cans usually have much lower dissolved oxygen and less air.”

That’s just one off-flavor — tastes that don’t belong — that Ogletree taught Akademia and Terrapin Beer Co. staff about during a recent seminar held at the brewpub. Participants sampled beer dosed with off-flavors to better help them learn about, and thus identify, these tastes in beer.

“Thankfully it doesn’t happen often, but off-flavors do crop up from time to time. Consistency is a key factor when judging a brewery’s offerings overall. When a new batch of beer is ready to serve, it is imperative that any changes in flavor are explained — has the recipe changed slightly, or is that flavor undesirable?” said Sarah Dupuy, an Akademia server and bartender who attended the seminar. “If the staff is educated in what flavors are undesirable, they can better judge whether or not a beer is fit to serve, and make sure the customer is always getting a quality product.”

Detecting off-flavors

The off-flavor Dupuy noticed most was that of diacetyl, which Ogletree also said is his least favorite.

“Diacetyl is butter or butterscotch. It’s like artificial butter or cake icing. I am very sensitive to it,” Ogletree said. 

Diacetyl gives the illusion of sweetness, and it comes from alpha acetyl lactate, which is naturally produced by yeast. If beer gets warm or is run through a dirty line, the alpha acetyl lactate can turn into diacetyl. 

“I love buttered popcorn. My favorite flavor of Jelly Belly is popcorn. But as soon as they opened the diacetyl beer, it smelled like a movie theater that hadn’t had the carpet replaced in 20 years and I wanted nothing to do with it,” Dupuy said.

To prevent this off-flavor, Ogletree said brewers can cold-condition their beer for a couple of days, then warm it back up to 68 degrees for two days. That puts the yeast to sleep, then wakes them back up, and there’s nothing to eat but the alpha acetyl lactate. Once that is taken out of solution, there’s nothing to turn into diacetyl and give beer the off-putting butter notes.

“If you’ve ever had a beer that was like sucking on grape skins and made your mouth dry out, that’s astringency,” Ogletree said, adding that it’s an off-flavor that usually comes from grain husks added during the brewing process. “The grain husks help provide a filter bed, but if you do that too warm with water that’s too hot, all those tannins get sucked out of the husk and make our beer dry and pucker-y and astringent.”

Other causes of astringency are wild yeasts and high-alpha acid hops. As for beer that is meant to have some wine-like flavors or notes, Ogletree said it’s possible to get the proper flavor qualities without tannic properties by adding grapes or grape skins after the beer is fermented, so they’re not exposed to heat.

Sarah Abad, an Akademia Brewing Company server, waits for her next sample of beer during the off-flavor seminar.

And if your beer smells like a Band-Aid, that’s a sign of phenolics. Some beer styles are meant to highlight these flavors (think Belgian ales, Christmas ales and hefeweizens), but on others it’s an off-flavor that comes from wild yeast.

Sarah Abad, an Akademia server who attended the seminar, called this one “the most detestable.”

“To me it tasted like a shoe,” she said.

When off-flavors are “on”

Depending on the style of beer, an off-flavor might actually be a desired characteristic. Esters, which offer Belgian and English ales flavor notes of cherry, stone fruit and kiwi. Although some esters are necessary for certain styles, they can still be overpowering.

“Esters are the fruity qualities of beer,” Ogletree said. “There should be almost no esters in a lager, preferably. [In ales] most of the time the esters that are there are good. The problem is when the esters get out of control and that’s all you can taste. That’s what happens when the beer is fermented too hot. If you ferment a beer at 90 degrees it’s going to have a lot of esters. If your cooler ever goes out, you could have a really ester-y beer.”

Lactic acid, if used properly, is another off-flavor that is “on” point in styles like Berliner weisses and goses. It adds the crisp, tart bite in sour beers, and can come from controlled additions of lactobacillus bacteria. Take, for example, brewing Niobe’s Tears gose or Everything He Touches tart brett saison, which undergoes kettle souring.

While the wort is still in the boil kettle, lactobacillus is added and sealed inside the container overnight. The next morning, the wort is soured. The wort is then heated back up to boiling so the bacteria are killed, but the crisp, sour flavor is preserved.

Though fruity flavors are OK in some beers, vegetable-like notes are less so.

“Dimethyl sulfide is corn, cabbage, vegetables,” Ogletree said. “It’s horrendous and something you do not want in your beer. The best way to get rid of it is to boil the hell out of your beer.”

DMS can also present as a flavor of shrimp or shellfish, and Akademia head brewer and co-founder Morgan Wireman said it’s a common off-flavor that comes from pilsner malts that weren’t boiled long enough.

Wireman was most sensitive to the tannic and diacetyl off-flavors. He said it’s important that Akademia staff learn about these undesirable notes so that they can answer any questions customers have about a flavor they perceive in the beer, and can then bring up potential quality issues with brew staff.

Craft beer guru Owen Ogletree, left, talks with Akademia’s head brewer and co-founder Morgan Wireman during the off-flavor seminar.

“We follow very strict procedures for sanitation and fermentation. We’re constantly testing and making sure that the flavor profile is developing like it should,” Wireman said. “If it’s brought to my attention that there’s a potential off-flavor, there are scientific methods for confirming if certain flavors are, in fact, present.”

These tests can also show if an ingredient in the beer is giving off a false positive. For instance, when Akademia’s IQ IPA recipe was being perfected, the very first batch supposedly  had a diacetyl flavor.

“When we did the testing to see if there was diacetyl, there was no diacetyl present,” Wireman said. “One of the hops in the first batch actually gave off a characteristic that could be perceived as diacetyl. We’ve since taken that hop out of the IQ recipe.”

He said if tests ever did confirm the presence of an off-flavor, the beer would be pulled from sale and potentially dumped — an unfortunate decision that’s part of being a production brewery.

“For instance, Dogfish Head dumped a batch of 120 Minute IPA because it wasn’t right, and it was a quarter-million dollars down the drain. They have strict quality control so they didn’t want to release it if it wasn’t up to their standards,” Wireman said. “Akademia is the same way.”