Good Beer Hunting

Into the Wild

Cereal Killer — Why THP is Bad for Beer and What You Can Do About It

Every time I open a beer I’ve barrel-aged at Creature Comforts, I ponder a bit on how it got there. Many of these bottles have more than a year of life in them. That’s not just a year for the beer, either. It’s my own life, too.

I think on where I was when I decided to make the beer, the flavor journey we embarked on, the raw material I wanted to try, the tweaks I wanted to make during the process, the vision that went into it—all sorts of stuff.

And at that moment in time, in that glass, how have all these things culminated and created a beverage? Taking myself out of the equation, what’s this orchestra playing for me? Are all the instruments properly tuned? More often than not, the symphony isn’t ready.


This journey of reaching the finish line is often months after the beer goes into the bottle. I wait and wait and finally there’s the moment when it all clicks. The noise becomes a chord as the off flavors have subsided and the blend shines. That’s when we release the beer, and not a moment sooner. And even then, I’m often worried if we’re still too early for a good hang.

Of all the potential party crashers, my biggest concern as we reach that last step is THP.

Tetrahydropyridine is an off flavor, an out of tune instrument in the orchestra. It lingers in my mixed fermentation beer for some time, often taking months to clear. This molecule’s flavor is often likened to Cheerios or cereal bars or urine. People sometimes even describe it as “mousy.” It’s a plague on mixed-culture beers. Speaking with other brewers, it seems to me like everyone has a different experience. Some only briefly detect it during their conditioning and then it clears quickly. Todd Boera at Fonta Flora has a bit of a more direct relationship with his bottling techniques:

“How long it takes for the THP to clear up depends directly on what yeast/cultures we dose for bottle conditioning,” he tells me. “If we use our house mixed-cultures or Brettanomyces strains, it can take 2-6 months in some cases. If we bottle condition with wine yeast that number tends to be at the lower end of the range.”

How long it takes for the THP to clear up depends directly on what yeast/cultures we dose for bottle conditioning.
— Todd Boera, Fonta Flora

Unfortunately, my experiences with THP are similar, and we’ve seen it is a problem that can be detected up to half a year or more. Sadly, there’s still a large number of producers that seem to be completely blind to it. Or, worse, they know it’s there, but think consumers won’t notice.

Not every person can sing with perfect pitch, or has the vocabulary to explain why a Van Gogh is better than a Thomas Kinkade, or can write about the flavors that separate a 3-star Michelin restaurant from a hot food truck in the neighborhood. But there are still some things that, collectively, humans tend to agree on. It doesn’t take words. It doesn’t take expertise. If you ask enough people about their favorite practitioners of an art form, there’s an “it” factor that separates the greats from the less-than-greats.

Off flavors, while not detectable—or even necessarily displeasing—to everybody, are roadblocks to a masterpiece. “The flavor is so overwhelming that it masks the intent of the beer,” Wild Heaven Beer Brewmaster Eric Johnson says. And what’s hiding behind the Cheerios? It’s subtleties, it’s structure, it’s beauty without distraction. It’s what we all love when we crack a bottle and taste greatness.

So if that’s the case, why does it keep showing up in beer?


The biggest roadblock is that there are more questions than answers surrounding THP right now. Historically speaking, there hasn’t been much research into mixed-culture beers, so the knowledge pool is shallow. It takes money to do much of this research, and acid-forward beers have only recently had any amount of substantial commercial success. When we opened Creature Comforts just more than four years ago, it was practically unheard of to put a Berliner Weisse in a can. It’s hard to remember life before canned tart beers, but market penetration for acid-forward brews is still very new.

The full understanding of the Cheerios flavor wasn’t even commonly linked to THP until recently. Just three years ago, The Mad Fermentationist wrote: “Brettanomyces produces tetrahydropyridine (THP), which at low levels provide a toasty flavor (at higher levels the perception of THP shifts to urine, or euphemistically "mousy."). I suspect this compound also plays a role in the ‘Cheerios’ flavors bottle-conditioned sours often temporarily develop.”

Usually, if a beer topic is talked about often enough in a technical sense, there’s a decent amount of information and research behind the subject. For THP, this isn’t the case. It’s increasingly commonly spoken of, but with few answers. Here’s an average interaction I have at festivals while catching up with other mixed fermentation brewers:

“Hey, how are you? It’s really good to see you. Found any Pilsners yet? Cool, cool. So, what’s the longest you’ve noticed THP last after bottling?

While the mysteries of THP can’t be solved by a quick Google, the conversational hum is getting louder. The topic is coming up on podcasts—Sour Hour, for example—more often, and independent research is starting to get shared through community wiki pages like Milk the Funk.

Hey, how are you? It’s really good to see you. Found any Pilsners yet? Cool, cool. So, what’s the longest you’ve noticed THP last after bottling?
— Hypothetical Mixed Fermentation Brewer

That being said, there are a few bases of understanding w/r/t THP. First, it’s produced by Brettanomyces and generally more so in the presence of lactic-acid-producing bacteria (or LAB), which also can produce THP. Exactly why more or less is produced is unknown, as well as the factors at hand that contribute to more. Oxygen is thought to play a large role in the production, but exactly how that works isn’t very clear. Anecdotal conversations with other brewers support this, and likewise for myself at Creature Comforts: we generally only see THP in beer after bottling (which, of course, has an inherent exposure to oxygen).

Where it goes, to the best of my knowledge and research, is not currently known. Like most off flavors that come and go through bottle conditioning, most folks believe it’s metabolized in some form and goes away. Along with other benefits, we choose to bottle condition every beer from our mixed-fermentation program to encourage this metabolism. Fonta Flora’s Boera also agrees that “bottle (or keg) conditioning is really the only thing that helps clear up THP in a beer.”

There are, however, many mixed-fermentation beers out there that are not bottle-conditioned. Unfortunately, this is where I see higher instances of THP. The general consensus right now is to limit oxygen exposure, bottle condition, and do so with healthy yeast. It seems if you do all these, THP will go away eventually. Fingers crossed.

Of course, where there’s uncertainty and a lack of research, there are also a range of theories. “The lion’s share of the assumptions that are out there are false,” Wild Heaven’s Johnson says. “I’m 99.99% sure that it’s a heat degradable molecule and can be removed with temp.”

Johnson says he expects to have concrete answers in the next few months.

Just to be perfectly clear: brewers aren’t making beers with THP because they hate the world, like to annoy brewers like me, or have a secret love affair with Cheerios. (Although one nationally known brewer did tell me at a festival once that he releases beer knowingly with THP because he doesn’t want to wait to clear and accepts it as a profile to that beer.) Ignorance, production constraints, conditioning space, and many other factors weigh in heavily. These are businesses that have to make cash-flow decisions, and if the market continues to not reward beers without THP, then why would they change? That’s the real world for many in this quickly growing industry.

To move forward, we need institutional support. It has to become a common conversation at guild meetings, at the Brewers Association, in research institutions, in breweries, and at the pubs and restaurants that serve this beer. If the consumer doesn’t demand it and if there isn’t money behind it, it will be hard to make any major strides.

Luckily, there is change on the horizon and many breweries are working to learn more. Earlier this year, Allagash brewmaster Jason Perkins started a THP research project of sorts. He saw great opportunity in an intern this summer, having her dig into the subject using a gas chromatography-mass spectrometer to start quantifying the compound. He remains optimistic for the future. "I’ve got nothing of substance for you now," he tells me. "In a few months, I might have more to say that has meaning."

Along with Allagash’s research project on the matter, Creature Comforts is also looking into a genetics study to help identify organisms in mixed cultures. It’s research that I believe will help link more information to the production and metabolism of THP.


The brewing industry loves hops, consumers can’t buy enough IPAs, and they’ll wait through the night to get cans of them. Consequently, there are research institutions dedicated to learning about hops. Thomas Shellhammer’s lab at Oregon State University is legendary—year after year, amazing hops research comes from that program. This makes sense when you consider the amount of money in hops in the overall industry and the farms in Oregon and neighboring Washington. The consumer is demanding this beer, so of course brewers want to make sure it’s as technically perfect as possible.

But what’s the home of mixed-culture off flavors?

The lion’s share of the assumptions that are out there are false. I’m 99.99% sure that it’s a heat degradable molecule and can be removed with temp.
— Eric Johnson, Wild Heaven

There are some historical parallels in the wine world. Minimal intervention wines that have low SO2 and consequently see many of the same organisms to fermentation as we see in mixed culture fermentation beers are where more instances of mousiness occurs. In fact, “mousy” is a term carried over from the wine world where people are literally considering the flavor to be something like rodent breath or a place where mice have taken up residence. More than 10 years ago now, The New York Times wrote about the impact of Brettanomyces and lactic acid-producing bacteria on the production of this flavor

To bring both industries forward, the testing that needs to be done is in labs or breweries that have very expensive equipment and time. Unfortunately, a GCMS costs about as much as a house, so you won’t see a lot of them at your neighborhood beer maker. Until there’s an institution with very real money that’s willing to put in the work, we may just be spinning our wheels and asking questions with answers that can only be found by sitting on our beer patiently for months at a time. Not many neighborhood beer makers do that, either.

But the next time you’re at your favorite bar drinking a mixed-culture beer, ask yourself if there’s a strong finish of Cheerios. If there is, ask yourself if you’d prefer that flavor not to be there. I’ll tell you that many like myself agree it’s a flaw. It’s the wrong note in the melody. It’s out of key, and the only way to fix it, for now, is time and practice. Start a friendly conversation with those around you. The bartender, the brewer, the patron. Maybe if we’re loud enough, this research will happen and we’ll start to make our way out of this dark age of cereal.

Words by Blake Tyers
Illustrations by Charlotte Hudson