Monthly Archives: December 2010

Nothing new until 2011

I’m installing a new lab this week and go on vacation next week, so I won’t really be in a position to post to the blog for a little while. Even after I get back, we’re remodeling our lab office and putting in new furniture then I train a new hire, so it may continue to be sparse but I’ll try hard to get something out.

Thanks for being patient.

Happy Holidays and Merry Christmas!


Does this make sense?

So I was watching Brewmasters on The Discovery Channel the other night (about Sam Calagione and the Dogfish Head Brewery) and the episode was “Grain to Glass”. The “B-plot” of the episode dealt with a batch of their 120min IPA in a stuck fermentation back in June where the batch started at about 32 Plato and never got below 9 Plato. They were trying to figure out what the problem was, so they went back and pulled some bottled 120min IPA from storage and tasted them. I don’t know how many they tasted, but there was one from 2008 and one from 2006, at least. They decided the one from 2006 had the characteristics they were aiming for, and then implied that they used the notes from that brew to influence the recipe for the brews going forward.

The problem is, beer is not a static and shelf-stable product. Unless the beer is kept cryogenically frozen (generally -80C or less), it will degrade. Even the “bigger” beers which use many dark malts and have high alcohol will be altered during storage, for better or for worse. While some beers may be altered less than others, it seems a bit foolish to base recipe modifications on a sample of beer which is no longer representative of what that beer tasted like when it first hit the market.

Of course I could be missing something. Television editors are known for spinning the story in whatever way they want, and their lack of familiarity with the subject matter would make it easier for them to accidentally mislead.

On a side note, I also noted that Dogfish Head “tested” their sensory panelists with the FlavorActiv standard for “Musty” (trichloroanisole – “cork taint” for you wine enthusiasts). They must have intentionally picked that particular one for filming day, since Musty is literally one of the two easiest FlavorActiv standards to identify at the usual 3X threshold level, and it would have looked better for the camera if all their panelists were seen picking the right one. Now if they did this with FA’s “Kettle Hop”, “Grainy”, or “H2S” standards, I’d be impressed.

And while I applaud the presence of the craft brewing industry on television, I can’t help but think that this show is just a giant ad for Dogfish Head…

Update: I’m still here

I realize that posting has trailed off a bit over the last week or two, but never fear: I’ve not given up!

I’m in the middle of a transition period at work where I’m helping to install a new lab and train new people to take over some of my duties. After this I’ll be focusing on sensory, and will have more time to spend on this blog.

I swear!

Say “Cheese”! Isovaleric acid in beer.

Cracking cheese, Gromit!

Have you ever smelled cheese in your beer? How about dirty sweatsocks? It’s more common than you may think. If you’re a homebrewer and you don’t use your hop supply as fast as you should, or if you store them improperly, you may be familiar with this aroma. This is isovaleric acid, and it’s a short-chain fatty acid commonly found in cheese, the valerian herb, foot odor, and sometimes beer. Now that’s an interesting selection of sources!

The commonly accepted threshold for isovaleric acid is about 1ppm, but like most other aromatic compounds, this can vary greatly depending on your genetics. This brief article gives some information about the genetic component of isovaleric acid receptors, exploring some of the sources of variability in how subjects perceive this compound. One of the more interesting things mentioned is that its detection threshold can apparently differ between individuals by up to 10,000 times. Personally, I think my nose has what I call an “acquired anosmia” to this compound. To be anosmic to a particular compound means you can not detect it at any concentration. While my case isn’t that dramatic, I think my sensitivity has dropped due to being frequently exposed to the purified compound when I spike it into my samples (despite using a fume hood and taking protective measures, it’s still possible to get it on you). If you get this stuff on your hands, you’ll stink for the rest of the day, if not longer. For this reason, I often have a hard time being able to tell if my spiked samples are at an appropriate level for the panel. Many times, I have to trust my math more than my nose.

So, how does isovaleric acid get into beer? Most of the time, it’s formed when hops get old, particularly when the alpha acids degrade. I’ve discussed hop acids already in the bitterness article, so if you need a quick overview, head over there and it might clarify some things. This image (from the above-linked article) shows the basic structure of the alpha acids (on the left) and the iso-alpha acids (right) that they isomerize into during boiling in the brewing kettle (at which time they become the source of bitterness in beer). Basically, there are 3 main types of alpha acid (and the 3 corresponding iso-alpha acids) and while they have the same basic structure as each other, there are differences at the “R-group” (top right of the molecule in the images). The differences are minor, but these minor differences can be interesting and influential nonetheless. One of these 3 alpha acids (humulone) has an R-group which is called an isovaleryl group. When this alpha acid oxidizes (due to age and/or improper storage), this R-group can be removed from the molecule and becomes flavor-active, leading to the cheesy/sweatsock flavor I’m on about.

Another way isovaleric acid can get into beer is through a Brettanomyces infection. It’s not the most common source in beer, but infection by this yeast genus can produce cheesy aromas, as well as a host of other undesirable flavor-active compounds like acetic acid (vinegar), 4-ethylphenol (bandages), and 4-ethylguaiacol (smoky). Some breweries intentionally “pitch” Brett into their fermentors as they try to achieve a certain flavor profile or match a particular Belgian style, but more often than not a Brett infection is a bad thing. Brett is also used in winemaking to achieve certain flavors, but it can also be a spoilage organism here depending on the intent of the oenologist.

So limiting undesirable isovaleric acid levels in your beer comes down to using fresh and high-quality raw materials (store hops in a cool, dark environment and, if possible, oxygen-free), and maintaining sanitary brewing conditions and using plentiful and healthy yeast to limit the potential for beer spoilage.

Jackpot! The Beer Fishbone Diagram

This PDF is a bonanza of information, enumerating the multitude of factors involved in all sorts of beer phenomena. It’s called a Fishbone Diagram, and the reason is obvious once you see it. I can’t even begin to explain everything that’s in here, I mean it would takes hours (days?) to pick it apart.

It’s pretty easy to interpret, although it is a bit of an information overload. Each page explains the various factors that influence a particular quality issue in beer. For example, below is a screenshot for the one of the pages [!] about how packaging and brewing issues interact to promote or limit beer oxidation. Other issues covered are controlling beer pH, fusel alcohols, H2S levels, foam quality, beer stability, yeast flocculation/vitality/viability, etc etc etc.

Brewing/Packaging Parameters and Beer Oxidation

You can find it here:
[see below]

Please excuse the rotated table of contents; I rotated the PDF so that the first page was the only one (of 42) that you needed to crane your neck to read. Better yet, print it out and enjoy it with a pint or two of your favorite beer. I’m going to go get a blonde ale out of the fridge right now.


Edit, 1/6/11:  Looks like these fishbone diagrams were developed by Greg Casey, recently (currently?) of Coors Brewing.  I hope it’s OK that they’re posted here…

Edit, 1/2/13: I’ve recently been informed that the file on the host site disappeared, so I’ve rehosted it at another site. If it disappears again, shoot me an email and I’ll try to get it back up.

Edit, 1/23/13:  At the moment, the free file-hosting websites I’ve been using don’t seem to have much of a shelf-life.   Either that or Greg Casey has a Google Alert on “beer fishbone diagram” and every time he sees the file posted he submits a takedown request to the hosting site.

Anyway,  I’m going to do this on an on-demand basis.   If you’d like a copy of the Beer Fishbone Diagrams, email me (found on “About” page) and I’ll get you a copy within a couple days.