Category Archives: Quality

It’s alive!

I’ve just finished relocating to a new city so it seems like a good time to dust off the ol’ blog and create some content!  Let’s pretend that I haven’t left you all hanging for more than a year without any new beer sensory science content and get down to it with a short literature review:

Many brewers and beer aficionados already know that one of the first ways that beer degrades as it ages is by the loss of the hop aromas which are often considered to be marquee flavors in many products and styles.  As such, if one wants to know how to extend the shelf life of beer and maintain a fresh-tasting product for as long as possible some investigation into how these aromas are lost is warranted.

This paper explores the various ways that hop oils (a major source of hop aroma) are lost throughout the shelf life of beer and focuses mostly on the loss of the aromas into packaging materials like the rubbery plastic liners under the bottle caps or crowns.  It was published in the Journal of the American Society of Brewing Chemists in 1988 and written by Val Peacock and Max Deinzer – a former AB chemist and hop guru, and an experienced analytical chemist from the Oregon State University chemistry department, respectively.   Both of these men have been extensively involved in beer research for years, and hop research in particular, so they know their hop chemistry; I can’t think of many too many more researchers more capable of attacking this question.  Let’s see what they have to say about this.

First, the researchers present data from some analyses they performed on commercially-available products:  a “super premium American brand” (Beer 1), a “Central European Import” (Beer 2), and an “American product from a mini-brewery” (Beer 3).  Flavors were extracted from these beers via continuous liquid-liquid extraction with dicholormethane and prepared with 2-octanol as an internal chromatographic standard.  In addition to analyzing the beer itself, they removed the foamed-PVC crown liners and extracted them in hexane prior to being made up for gas chromatography/mass spectrometry analysis.  Relative concentrations of analytes were calculated by finding the ratio of the amount found in the beer vs. the crown liner.  Analytical results for roughly 36 flavor-active compounds (15 from hops) are presented, with concentration values for both the beer and the crown liner indicated.   Overall, they found that the more polar, or less oily, the compound, the less it migrated into crown liners.  Therefore, alcohols and the water-soluble esters (like isoamyl alcohol and isoamyl acetate) were not found in liners in any appreciable levels (0% and 2% found in crown liners, respectively), while the non-polar compounds, like the hop terpenes and sesquiterpenes myrcene and humulene as well as the long-chain fatty acid esters, were found only in the crown liners.  Other hop aromas, like terpene alcohols, linalool, and geraniol, were only found in the beer.

In order to understand the rate of uptake of some of these compounds into the crown liners the researchers created model systems of non-carbonated 3.5% and 3.0% (v/v) ethanol/water solutions and spiked known amounts of several hop-derived compounds, then re-crowned the bottles and stored them for 18 and 28 days, respectively.   In the 18-day 3.5% ABV model, 79-87% of the hop-derived hydrocarbons (myrcene, caryophyllene, and humulene) were lost to the crown liners.  As was seen in the commercial beer analysis very little, if any, of the water-soluble compounds were detected in the crown liners.  In the 3.0% ABV model system after 28 days of storage, the researchers found that only small amounts of the oxygenated hop compounds (alcohols, epoxides, and diepoxides) were captured by the crown liners.  Some of the results ran counter to what was seen in the previous analysis, and it was speculated that either some of the compounds degraded by oxidation after they were captured by the liners, or that the 3.0% uncarbonated model system was different enough from the other beers analyzed and that this unpredictably affected the results.

Finally, the researchers looked at the rate of decomposition of four hop aroma compounds which they had spiked into a “premium American beer” (implied later to not be a pilsner):  linalool, geraniol, humulenol II, and humulene diepoxide A.  Beers  were stored at room temperature for about 60 days to simulate warehouse and market storage.  11% of linalool was lost after 57 days, and the steep-then-level nature of the decomposition curve indicates that the degradation of linalool is not a first-order reaction and implies that there are other factors at play in the decomposition of linalool – either that there is an equilibrium that is reached or that linalool is reacting with beer components that also get depleted over time, such as oxygen.  Breakdown products of linalool were analyzed in the final (57-day) sample and the amounts found only account for 10% of the lost linalool, which is somewhat puzzling – perhaps there are other breakdown products which were not realized in this study.  Geraniol behaved similarly to linalool:  12% lost in 56 days, with the majority lost in the first couple weeks and few anticipated breakdown products detected.  Humulenol II degraded much more rapidly than linalool and geraniol, with 66% being lost after 61 days.  While the decay curve isn’t as “curvy” as the previous compounds, it still leveled off somewhat.  They also found some additional compounds in the final sample which they guessed were humulenol II breakdown products, as there was none of these detected in the fresher samples, nor in the linalool/geraniol samples.  GC-MS results implied that both oxidation and acid-hydrolysis were at play.  Lastly, humulene diepoxide A decayed the fastest of the four compounds, where 84% of it was lost at 56 days in a nearly-linear rate.  Numerous supposed degradation compounds were detected, but the reactions are so complex that identification was not feasible.

Overall, this paper provided an interesting look into a couple of the main reasons that hop aroma is lost in aging beer:   adsorption/absorption into crown liners (and likely aluminum can liner material as well!) and oxidation/acid hydrolysis reactions leading to their conversion to other compounds, both flavor-active and not.  When one considers both the importance of hop aroma to so many craft beers and the fragile nature of hop aroma, it seems like some attention should be paid to maintaining sufficient hop aroma over time.


Fate of Hop Oil Components in Beer. Val E. Peacock and Max L. Deinzer, Department of Agricultural Chemistry, Oregon State University, Corvallis 97331. J. Am. Soc. Brew. Chem. 46:0104, 1988.

Macrobrews: “Crap on Tap”?

Perusing the latest issue of BeerAdvocate, I found a letter in the Feedback section referencing an article that I could tell I just had to find: Andy Crouch’s “No Crap on Tap” article.

In this article, Andy lambastes the tendency for many craft/micro beer drinkers to describe beers from the Big Breweries as inferior, poor quality, “crap”. He bemoans the use of catchy rhyming cliches, like saying that your favorite pub has “No Crap on Tap” or, in other words, they don’t sell any Budweiser or its ilk.

It’s refreshing to hear more people voice the position that these macrobrews are far from “poor quality”. It’s something I’ve been saying for years.

In a nutshell: these beers are made to extraordinarily tight specifications, from the raw materials all the way the to finished package quality. They are made to meet amazing levels of consistency from different production facilities across huge geographical distances . The lack of flavor that they have compared to craft beers is not, in fact, a mark of inferiority but rather the mark of a beer that has nowhere to hide any flaws: the slightest slip-up in production means that faults in the flavor would stick out like a sore thumb.

What YOU should do about it: feel free to express your opinions about how lovely or how terrible that beer tastes. But realize that they are just that: opinions. Try not to conflate your opinions with your perception of quality.

Overall Difference Tests

Let’s change tack a little bit here and discuss a specific set of sensory tests: overall difference tests.

Deciding whether two samples of beer are different is not as easy as it may seem. Everyone perceives their senses slightly different than others, so what one person may find to be a noticeable difference may only be detected by few, if any, others. Various types of bias may also lead people to find differences that don’t exist. On top of this, the need for accuracy in your data means that you often need more than just a few people to be able to truly say whether there is a difference. So, as with all laboratory procedures, there are standardized methods and tests that are used when searching for differences in food and beverage systems. Even under the heading of “overall difference tests” there are a number of different tests that can be used, each with their own pros and cons.

Overall difference tests are used to find whether there is any detectable difference between two samples. Where exactly that difference originates is not necessarily part of the goal of the difference test, although you can usually pull out some hints to help guide your progress. This type of test differs from the more specific “attribute difference test” which seeks to determine whether a difference exists on the basis of one specific aspect of the sample, whether it is the color, the bitterness, the phenolic aroma, etc. I’ll discuss attribute difference tests later, but before we move on to the tests themselves, a word about error first.

In statistical tests such as these, there are essentially two types of error: α-error, and β-error. α-error is a numerical representation of the risk you are willing to accept for the possibility of finding a false-positive, or finding a difference when one doesn’t exist.  β-error is the same type of numerical representation, but it signifies the risk you accept for possibly finding a false negative, or missing a real difference that exists between the samples. In practical situations, you must balance which risk you want to minimize over the other, since minimizing both requires many more panelists and samples than most production environments can accommodate. For overall difference tests it is usually the alpha that is minimized, while the β-risk is allowed to be large to keep the number of assessors reasonable. The default value for α is usually 0.05 meaning you, as the administrator, are accepting the possibility that there is a 1/20 chance that the results will indicate a difference when one doesn’t actually exist. An α of 0.05 isn’t required by any means, but it usually offers a good balance between risk-management and panel size.

What follows is a breakdown of a few of the more commonly used types of tests that can be used to find an overall difference between test samples.

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The IBU Assay

The spectrophotometer is among a small set of tools and equipment that are essential for a quality control lab to be adequately productive and accurate in a brewery setting. The reason for this is the BU assay which, apart from the HPLC, offers the best and most direct way to analytically measure the bitterness of beer that is available to brewers today. Relative to HPLC, the BU assay lacks precision, accuracy and sensitivity. But what makes it appealing are a number of things, foremost being the price: a couple thousand dollars can net you a new UV/Vis spectrophotometer and some supplies, whereas an HPLC can be an order of magnitude more expensive. Convenience, simplicity, and to some extent reliability are also among the benefits of this method, since HPLC, indeed chromatography in general, can be fickle and prone to error if rigorous procedures are not followed. Here, we’ll explore various aspects of the BU assay, including its origins and the fundamentals behind it.

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Does Guinness travel well?

Well, beer in general doesn’t travel well, so I’m going to guess “no”.

I ran across an article about a study by the Institute of Food Technologists (link in the sidebar) which sought to find out if there was any truth to the idea that Guinness served in Ireland tastes better than that which is served elsewhere. Their preliminary results indicate that, yes, Guinness served in Ireland tends to score higher in flavor preference to those outside the country, even after accounting for various variables.

I’m not surprised. In fact, I bet this is the case for most any beer in the world: it’s very likely going to taste better the closer you are to the brewery. This is because there is less transportation and time required to get the beer to various parts of Ireland compared to the rest of the world, meaning less time for the flavor to deteriorate from oxidation and aging. Also, Guinness probably has more influence over local bars and how they maintain their tap lines. This is also related to proximity; there are probably more Guinness reps combing the pubs of Dublin than there are in Boston. They also mention the affect on popularity and the effect on freshness: Irish pubs will probably be going through more Guinness than pubs elsewhere, meaning there is fresher beer on tap since the turnover rate is higher. All of these factors should be no-brainers.

Other thoughts I had when I read this was about the methodology. I haven’t read the paper, but I’m going to assume that all 4 researchers tasted Guinness in a number of different countries, and overlapped their territory, because otherwise there would be no way to control for the “assessor” variable during the analysis. I also note that in the abstract, they say their researchers were “non-expert”. I would have hoped that they would have had some level of beer flavor training, however basic, before undertaking this project. Another thing I wondered about is how they controlled for the “ambiance” variable. While they did mention the possibility that ambiance could affect the assessment of the beers, in the abstract they say the statistical significance remained even after controlling for ambiance. Now, I’m not sure how you can control for ambiance without tasting all the beers in a single location; it doesn’t make sense to me.

I was also a bit irked at the tone from the following passage, which seems to assume that the Journal of Food Science, or beer research in general, might be considered a non-scientific discipline:

That the Journal of Food Science is a serious publication can be inferred from some of the other material in the March issue. One feature is headed: “Technological Optimization of Manufacture of Probiotic Whey Cheese Matrices”. A second reports: “Improved Sauerkraut Production with Probiotic Strain Lactobacillus plantarum L4 and Leuconostoc mesenteroides LMG 7954”.

It’s almost like they needed to convince themselves that Food Science is actually science…

PS: the pint of Guinness I had at the Panorama Sky Bar at the end of the Guinness tour was the most expensive “free” beer I’ve ever had: 17€. But they poured a little shamrock in the head of the beer, so that’s got to be worth something, right? Of course the 17€ was for the tour of the “brewery” (read: “museum”), but really the only worthwhile part of the tour was the view at the top and the pint in your hand.

Brewing Technology Blog

I was just going through some of the links that have been sending traffic to my blog, and I noticed one of them was from a Tweet that Bill Simpson (from CaraTechnologies) made awhile back, calling it a “great blog about beer tasting”; awesome! Although he may not recall it, I’ve met Bill Simpson before and he is quite knowledgeable about beer and brewing. I suppose you’d have to be if you were a consultant for any number of brewing-related issues. Anyway, he’s sent some traffic my way, so I’ll send some to him. His blog is The Brewing Technology Blog and has lots of great information. Now, I’m telling you this in confidence that you won’t run off to some other blog and forget about this one. Fortunately, he seems to update his blog slightly less often than I do, but he also covers a broader range of topics than I do, too.

At any rate, check it out. It may be more suited for commercial brewers than homebrewers or beer drinkers, but there is information there that can be used by anyone.

Looks like someone beat me to it: how to find fresh beer.

I wrote a post last week asking for requests for production information on beer labels, in an effort to accumulate a database that you can reference in your quest to buy fresh beer.

Well, one commenter has enlightened me to the fact that this has pretty much already been done.  What a load off my back!  This could have been a huge and on-going project, and I’m a bit relieved that I don’t have to assemble and maintain such a list.

I’ve had a look over it and it’s huge, and from the entries I’ve seen, pretty accurate too.  Of course, breweries change their labels and equipment all the time, so there may be some inaccuracies hiding in there somewhere, but it’s a great start.

Fresh Beer Only.

So, find your favorite breweries in this list, and make a note of where and how they put their information on the label (hopefully they put something on there; there’s a disturbingly high number of packages that have no information whatsoever on them). Then when you’re standing in front of the beer aisle at the store, don’t be afraid to shuffle the bottles around in order to find the freshest. You deserve it.