Category Archives: Practices

The long road to Descriptive Profiling, part II

This is the second part to a three (?) part set of articles covering how to train a sensory panel to perform descriptive profiling.  It covers Intensity training and descriptive profiling lexicon (ballot) development.

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The long road to Descriptive Flavor Profiling

What do we have here?  Another Beer Sensory Science article?   Yeah, maybe a few.   I just recently gave a talk about something related to this, so I thought it might make a good subject for a blog article.  It’s a lengthy topic, so I may be breaking it up into multiple entries.   The trick will be posting them all within the same calendar year…

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The final word on beer serving temperature.

Sounds a bit arrogant, eh? Well, follow along and we’ll see if you disagree.

It seems like every week I run across some sort of discussion about what temperature to drink your beer at. These conversations usually involve some people (who are often fairly well educated in the various topics of beer) enlightening the beer n00bs of the best way to serve, pour, and drink various beers. This “best way” is most often dependent on the style of beer in question, with lagers being served colder than ales and other ideas like that. Well, I’m here to tell you that is a bunch of bollocks.

Now, don’t get me wrong: everyone who drinks or eats anything should know that volatile flavor compounds are more readily released and detected when the sample is warmer. The same with agitation: when you stir, swirl, swish, or chew your sample (be it solid or liquid) you’re allowing more volatiles to be released. Also, controlling serving temperature has great importance when conducting sensory experiments, not only for ensuring that all samples are treated in the same way, but also to maximize (or whatever the goal is) the chance of picking up certain flavors. These are all fundamental ideas in flavor science.

But beyond these considerations, my point is that once you are armed with that knowledge you should be free to enjoy your food or beverage in whatever way you like most. There are a number of instances where a beer will taste better when it is colder than it does after it warms, regardless of the style. I’ve experienced this many times, particularly when drinking beers from small microbreweries who may not have the control of quality parameters that larger breweries have. Some beers will be wonderful and defect free when drank below 40F, but after the beer warms in your glass some of the ugly defects that you didn’t notice earlier start to come out. Diacetyl is usually the culprit here, but it can be other flavors as well. Plenty of times I’ve opened a can of Heineken and poured it into a frosty glass and enjoyed the first half, but by the time I near the end of the glass oxidation flavors are starting to make themselves apparent and the beer becomes far less tasty. In these cases you almost NEED to drink the beer cold, regardless of whether it is an ale or a lager, just to enjoy it. Another reason I enjoy my beer colder is that it’s more drinkable and refreshing, and yes, I often like my ales drinkable and refreshing. Sometimes when flavors hide behind the coldness it can make the beer easier to drink. For example, beers that have higher alcohol and a lot of solvent-like flavors can be tamed when drank colder, while they can sometimes get more aggressive and unpleasant as they warm.

What might bother me the most about this serving temperature topic is when a pub will assume that this is the best temperature at which to serve their beer. Sure, it may be better for delineating the subtleties of the beer flavor, but what are those extra 10 degrees doing to the stability of the beer? It’s allowing the beer to oxidize and age that much faster, so while you may be trying to appreciate the beer now you are also making a poorer quality beer for the next pint.

What it boils down to is this: don’t tell me how to enjoy my beer. I know how and when to use serving temperature to achieve different goals, but when I am drinking beer because I just want to drink a beer, I will serve it at the temperature that I want it at, not what you think it should be. And I encourage you all to have the same mind set: if you like your IPA at 35F, that is your call and I won’t ever have a problem with it. I just hope you’re not under the impression that all the flavor you taste is all the flavor there is in that beer.

How to swirl wine.

It’s not really about beer, but it is about sensory analysis of food products so it will fit in here. And I just can’t pass up the opportunity to share it with you.

I stumbled upon this gem of an article written by a “very knowledgeable” winery tour guide from the Napa valley area. In it, he discusses how the aroma of wine depends on which way you swirl the glass, clockwise or counter-clockwise. The reasons he posits for this are… interesting. You’ll just have to read it for yourself.


Please also note the link at the top leading to an equally entertaining follow-up article where he further attempts to explain his wine prowess and reasoning.

Facepalm, headscratch, mouth agape, etc.

A pretty corny post.

One of the most ubuiquitous flavors in beer, present to some degree in pretty much every beer, is dimethyl sulfide, or DMS. It’s a normal part of beer flavor but, as usual, its acceptability is dependent on the intentions and desires of the brewer. It can be a large portion of the flavor profile of certain beers, while in other beers it is expected to be at much lower levels. For example, Rolling Rock is considered to be a prominent example of a beer which is high in DMS (although in the past it may have been swamped by skunky/lightstruck flavors as I believe Rolling Rock has not always been brewed with light-stable hop extracts).

DMS has the aroma of canned vegetables, particularly corn or creamed corn. It’s a small and simple molecule; as the name conveniently implies, it has two methyl-groups flanking a sulfur atom:

Typical flavor threshold for DMS in beer is about 35ppb, and beers from around the world can contain anywhere from 10-200ppb. Typically lagers tend to have a bit more DMS than ales do, but what dictates the DMS levels in your beer more than the yeast is the production parameters in your brewery, particularly the kettle boil and wort-chilling.

DMS is considered to originate from malt, although it is actually formed in the brew kettle. All malt contains a variant of the amino acid methionine called S-methyl methionine (SMM), and it is an intermediate in a number of biosynthetic pathways which plants use to make other compounds. SMM is pulled into the wort during mashing and lautering and as the wort is heated the SMM degrades and is converted into DMS. While the wort is boiled, however, the volatility of DMS allows it to be removed from the wort and out the ventilation stack to never return. If there is no way for steam condensate to escape from your kettle (like if your homebrew pot is covered during the boil) then that condensate will drip back into the wort returning that DMS back into your beer. In such a case, the SMM is still creating DMS because the wort is hot, but the DMS can’t go anywhere so it just continues to build up into higher and higher levels. For this reason, the whirlpool and/or wort-chilling stage after the boil is a critical time in DMS control: if the wort sits too hot for too long, DMS will continue to develop since there is no boil to drive off the compound. I recall some power outages here at the brewery which knocked out the brewhouse for a bit. The brew that was in the whirlpool at the time wound up staying in there for much longer than it should have, which lead to a beer with astronomical DMS levels. At first glance, you may think that controlling DMS might be as easy as making your boils longer to convert all the SMM to DMS and drive it out the stack, but there is enough SMM in most malts that this is not a practical solution: the boil times required to convert it all and volatilize it could be hours long and would be quite detrimental to other wort parameters and the quality of the beer. Some kettles are more efficient at stripping DMS than others, as well. A simple direct fire or steam-jacketed kettle would be less efficient at removing DMS than a kettle with a calandria, which would be less efficient than a Merlin kettle. In fact, I recall brewery which, after installing a Merlin-style kettle, wound up being so efficient at stripping volatiles from the wort that they had to “de-tune” the kettle to make it less efficient since it was throwing off the flavor profile of their beers.

Even after the wort is chilled to the point where SMM is no longer being converted into DMS, the whole corny story isn’t over yet. During fermentation, the carbon dioxide that is produced by the yeast has a scrubbing effect on the DMS, carrying some of it out of the beer. This happens more efficiently at higher temperatures since the fermentations are more vigorous, and for this reason ale fermentations are better at this than lagers. This is why many lagers tend to have somewhat higher levels of DMS than ales do.

Here is a pretty handy chart I found on the internets showing some data about the DMS levels in wort/beer over the course of production. You can see how the levels drop significantly during boiling, but how they can potentially rise again before the wort is chilled. Then they fall again during fermentation as the yeast help blow off some more of the remaining DMS.

Finally, another potential source of DMS can actually come from bacterial infection. Some species of Enterobacter can produce DMS, along with diacetyl. This is quite uncommon in normal production scenarios, but it could conceivably happen more frequently in homebrewing situations. However, the vast majority of DMS in beer comes from the malt and the boil, so if you have an issue with corny beer, check the brewhouse parameters first.

But the story of corny beer doesn’t stop there, no! A challenger appears!

As I collected various flavor compounds that I understood were in beer, I came across a reference to another malt-based compound which was described as “biscuity/malty”. I thought this might have something to do with the biscuity aroma which is a dominant malt flavor in beers which use Victory or “biscuit malt”. Well, I was wrong. As I opened the package of 2-acetylpyridine which Sigma-Aldrich had shipped to me, I realized “This isn’t biscuity at all. This smells like freshly cooked corn tortillas!” It was like opening up that container of steaming tortillas at a Mexican restaurant, or a bag of high quality corn chips. So that’s what my panel calls 2-acetylpyridine now, “corn chips” rather than “biscuity”. Wikipedia says that 2-ap has an odor threshold of about 60 parts-per-trillion, but other literature values I’ve seen indicate that in beer it is closer to 40 ppb (and my experience with it shows this to be pretty close).

2-acetylpyridine, as seen below, is found in malt (and corn chips) and is created by the Maillard browning reactions. These reactions take place when certain types of sugars are heated in the presence of amino acids. It’s a highly complex series of reactions that take place which lead to a whole slew of compounds, including flavor compounds and color compounds. It’s not caramelization, but it can be confused with it if you are unfamiliar with the differences. The browning of the bread as it toasts, the malting of barley, the browning of beef as it cooks – these are examples of Maillard browning reactions.

I’m not going to go much into 2-ap, but just brought it up to show that not all corn-type flavors in beer come from DMS. In fact, I’m starting to think that some of the flavors in our beer that I have previously associated with low levels of DMS might actually wind up being 2-ap and that’s pretty interesting.

Hope to post again soon! But probably not.

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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Bias: How easily we’re fooled.

In sensory science, we deal directly with extracting information from tricky and fickle systems:  humans which, as we know, are animals with brains just advanced enough to get them into trouble.  Particularly, we focus on what the subjects are experiencing from a sensorial standpoint and that, on its own, is a system which is easily confounded. This article is about the things that fool us:  the phenomena that occur around us which influence us and how we perceive reality.  It’s rather startling just how easily we can be tricked and even manipulated, and there are long and growing lists which detail our understanding of the “failures” which can be triggered in our sensory systems.  Of course these are general tendencies and not concrete rules that every human unknowingly follows.  But bias is a clear and present threat to the validity of all sensory data, and care and vigilance must be exercised by panel administrators in order to mitigate its effects.

First, we’ll discuss some of the more general ways that humans can be fooled, some of which you’ve probably seen before, then we’ll move into how it directly affects a sensory panel and even the average beer taster.

Probably one of the most famous examples of these failures of the human brain’s perception abilities is the selective attention test by Daniel Simons and Christopher Chabris from 1999. Basically the video shows you a small group of people passing basketballs back and forth and asks you to count how many times the balls are passed. If you haven’t seen it, follow that link and watch it. It’s only a minute or so long, I’ll wait here. — Great, did you see the gorilla? At one point in the video someone in a gorilla suit walks across the screen, right through the basketball game. The point of the exercise is, if you’re so attentive to the basketballs you can miss something which is right in front of you, even if it is quite absurd and out of place. It’s probably so famous that it’s hard to fall for it anymore, but it is a well documented experience.

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