Infection/Quality Problems: what we should know

Since this thread got resurrected I want to add another beer quality problem I've encountered a handful times over the last year...butyric acid. Here's a pretty detailed summary of it... http://www.milkthefunk.com/wiki/Butyric_Acid

Short version: Butyric acid is the chemical that gives vomit that distinctive, sharp, gut-wrenching odor and flavor, and it can be a flaw in beer. The odor detection threshold is much lower than the taste threshold, so it's very common to smell it without tasting it, but smelling it was enough to ruin the beer experience for me.

Interestingly, the beers I've detected it butyric acid in have all been "New England" style hazy, dry-hopped IPAs... and well-regarded ones too. Hill Farmstead Abner was the first I noticed butyric acid... it was really apparent in the smell, but it tasted OK (thankfully). I had my wife verify and she also smelled same vomit-like odor. .A few months later I caught some whiffs in Alchemist's Focal Banger, but nothing like the Abner. I might be more sensitive to butyric acid than others... we all sense things a little different, but there was a thread that came up a bit ago about someone getting similar off-smells in a beer, so I'm not the only one. Keep an eye [or nose] out!

 

Randy, that is entirely possible. Each individual will have their own taste threshold.

I am more sensitive to diacetyl than others. I once requested a sample pour from a brewery where I experienced diacetyl issues in their beers in the past. We (my wife, the bartender and myself) all had sample pours. I distinctly picked up the diacetyl, my wife said "there is 'something" there, and the bartender shrugged his shoulders and said he didn't pick up any diacetyl.

Cheers!

P.S. I have had a number of the so called 'NE' style IPAs from Trillium, Tree House, Bissel Brothers, The Alchemist, Hill Farmstead, Tired Hands,... and I have personally never picked up any butyric acid in any of those beers or any other beer for that matter. Maybe I am 'blind' to butyric acid? Or maybe this off-flavor occurs rarely?

 

Yeah, I might just be sensitive. I'll entertain the idea that maybe I imagined the butyric acid in the Focal Banger. The Abner though... whew...no doubt it had a vomit aroma and confirmed by my wife, but she didn't detect it as strongly as I.

I've had plenty of IPAs, NE-style or otherwise, where I don't detect butyric acid, so yeah it's not as common as other off-flavors. From the bit of Google research I've done the bacterium that causes it is a fairly common rider on malts and it's a tough little bugger that can survive in many conditions, even boiling! But, whether enough of the bacteria is about to create detectable butyric acid can be seemingly random. I read an anecdote from a brewer who reported losing a batch of a dry-hopped IPA to really high butyric acid and they say they narrowed it down to a bad batch of hops they used for dry-hopping. The next beer came out fine with new hops. Maybe it's the dry-hops that make these NE IPAs slightly more susceptible to butyric acid off-flavors? I don't know... the how and why is above my pay-grade... I just know it when I smell it.

 

@cavedave another round of applause to you for starting this very helpful thread.

The overall topic and general information about infection and its signs would definetly be a useful topic for the Beer 101 section of this site. Since the number of breweries and barrel aging programs seems to have been increasing in recent years it's becoming almost as important to know about as skulking. Skulking may be more common but infection may be more controversial and harder for the customer to understand and/or avoid.

Any chance @Todd that such an essay could go on the to-do list? (Might even be one that could be at least partly "crowd-sourced" with a few of the BA members who know something about infections, etc. contributing, exchanging drafts, etc. and with final write/edit being under site control.)

 

Delayed edit. "Skunking" not "skulking" (as my mobile device seems to think).

 

Especially when I'm new on the block and it is so easy to think any flavor I don't like is an infection.

 

By taste.

 

It is certainly important for new people to understand what aromas, flavors, and characteristics are supposed to be in one's beer. If not, you'll have a whole generation of beer drinkers thinking that their kettle soured Gose is supposed to smell like feet and rancid butter.

 

There is no way, but the percentages are VASTLY in favor of your beer getting infected via dirty tap lines than an unclean keg.

 

Aaaa . . . . not really. I'd put "producing phenolic aromas and flavors" as the first, with "oxygen scavenging" a happy side effect, but not even in the top three.

 

I've only come across one infected beer so far and it was a Duck Rabbit Imperial Stout - it tasted like tart cherry. I think we've all had skunked German beers do they qualify as Infected?

Pasteurization is obviously a simple answer to a huge problem. I used to work for a medical company located outside of Denver and we had a gamma sterilizer used on blood lines to kill anything and everything unwanted. We also had a contract with a local company to sterilize of all things boxes of chicken. Would something like this work on beer. Hell it would already be bottled and cased, it just runs thru the unit.

 

Infection and skunking are two different things, with very different causes.

 

If this table is to be believed, then butyric acid (in water) has a much lower odor threshold than taste (240 ppb vs. 6200 - 6800 ppd for taste). Older literature shows much different results, so you have to be careful interpreting what you might find. The detection limits for many things has dramatically improved, so those threshold numbers get refined as the ability to measure improves. Things that could only be detected in ppm can now be measured at ppb levels or even lower. I do gather that butyric is a more uncommon off flavor in beer, but not rare to the point of not happening - pretty sure we've all run across it a time or two in packaged beers.

Further down the list is diacteyl (in water)...much lower odor and taste threshold, again assuming the table is reporting accurately. What bothers me with this reference is there's no date, but they at least cite a lot of references. So I wonder if this is actual "work" or just a compilation of data we could all find with sufficient Googling. You'd think there would be a similar compilation for "beer faults" with the odor and taste thresholds listed, but I have yet to find one. There probably is one, just harder to find.

It would be handy to have a tabulation of beer off flavors, how they happen, what they might present as to our senses. Even one as simple as Palmer's summary pages would be a good reference and maybe just a link would suffice (assuming that would be legal, of course). Off flavor descriptions seem relatively easy to find via search. The little skimming I did of a few references shows to me that the information is just as fraught with hyperbole as most things on the interwebs...the challenge of finding the credible source, in other words. I think a lot of people have probably tasted beers with flaws and not know they were flaws (certainly explains how a few of my local breweries stay open). With the number of casual beer drinkers today, I think many don't know they have tasted something "off". I know I have tasted something odd and wondered whether it is "supposed to be" or not, especially when I was less experienced. When I find something "odd" in a beer flavor I'll asks somebody or do some digging to figure it out but I imagine most people don't. I've also had the benefit of sensory training at work - and it is pretty damned disgusting especially when we get to the "off flavors" kit...takes a while to recover from that session! But at the least the training gives me a sense for what should and shouldn't be in the broadest sense.

 

Do you have actual numbers on this? I do not think it to be correct. Also, water and alcohol molecules are MUCH smaller than bacteria and yeast, which should not be able to get through the staves, croze, or the sealed bung of a wooden barrel.

No, not in any functional way.

35 year old barrels are certainly not left dry for that long or else they wouldn't be able to be used, without significant restoration. Having liquid in them for that long preserves the integrity of the barrel. Once barrels become neutral, from a flavor standpoint, they can still be used as aging vessels, if wood and/or spirit character is not sought after in the beverage that is stored within them. Barrels that are cared for well can last many, many years without having to be replaced.

 

So far as I can tell with a quick spot check, the table is most likely as good as it's going to get. The Leffingwell research results get multiple citations in reasonable journals and so seems accepted by other researchers.

The important caveat will be the one you point out by saying "(in water)" since the interactions with other flavor detection things going on in a more complex tasting environment. (As near as I can tell by water, they are talking as flavor free as you can get it, e.g., something like distilled water.

 

So light struck beer is exactly what then? Light alters things so it has a cabbage smell, so what is that? Serious question, skunked isn't an infection?

 

Note: I probably should have mentioned more detail. Infections are caused by micro-organisms. (None of those in beer are harmful to humans.) Skunking is caused by UV light interacting with a chemical in beer that is there because of use of hops.

 

Check out this Video



Then take a look at the Beer 101 discussion of skunking.

If you want a bit of the chemistry, the guy who wrote the blog post linked below goes into that sort of stuff.

https://beersensoryscience.wordpress.com/2011/03/17/lightstruck/

 

I agree about the water. All I can say is when I went through training, everything was initially in water so we could develop a mental "scale" and common language. For example, sweetness was simply sucrose in water so you could develop an idea of "intensity" with no other contributing factors. It gets much more difficult when trying to pick out the sweetness intensity when it is surrounded by sour, bitter, astringent, etc. So tasting "pure" tastes in water gives you a tape measure, so to speak, but it does differ when it is "for real". But I also know if I alter the product by removing acidity, it is not just the sour attribute that changes in terms of perception and it doesn't just taste more sweet. Changing one attribute changes the entire sensory profile.

Then we went on to "spiked" samples of our products - some are much easier to unravel than others and usually what we're looking for is big swings - like somehow a batch is massively over-acidified or has too much of a flavor package. The off flavors - usually looking for something much less "obvious" and it was difficult. It's fairly easy to say something is too sweet, too sour, or has too much XYZ flavor. The off flavors we have are pretty subtle and can be easily overlooked.

It was "no joke" training - very intense, and at times quite unpleasant! I remember people walking out after tasting straight mayonnaise - nothing to do with what we make, but it was part of the training tools and good vehicle for delivering some "surprises" and learning to pick things out of a mixture.