Tag Archives: aroma

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.


Yes yes, I know. You’re right: it’s been far too long since I’ve posted. Well, I’m going to try to make it up to you with a nice article about one of the most influential and ubiquitous flavor components of beer: esters. I bet you’ve been waiting a long time for this article.

So, what are esters? If you ask a chemist they’ll tell you that esters are a class of molecules which contain a specific type of functional group called an ester group, if you can imagine that. These ester groups are made up of an oxygen molecule double-bonded to a carbon which is immediately adjacent to another oxygen which is bonded in-line with the carbon chain of the organic molecule. Perhaps a picture would illustrate the concept well.

A generic ester.

Looking at that picture we see a portion of a larger molecule, where the R-groups represent what could essentially be any kind of organic chain. The ester group consists of the carbon and the two oxygens that are bound to it. Esters, due to the variation that can occur at those R-groups, are found in many shapes and sizes, but they all share the common feature of the ester group. The smaller weight esters are quite volatile and are frequently used in the production of food products and fragrances; they are largely responsible for much of the flavors and aromas associated with many types of fruits. Larger weight esters are also found everywhere, from DNA and plastics to triglycerides and explosives (nitroglycerin).

More after the break. Continue reading

Genetic diversity in olfaction is larger than previously thought

I ran across a short article over at Scientific American, and while it didn’t contain too much information that isn’t already known, it did describe some new research that says that the genetic diversity in how we perceive aromas may be larger than we previously thought (which seemed large already).

Here it is, and it shows just how difficult the job is for someone studying the human senses. How do you know that a particular panelist is responding to an odor the same way another is? Well, you don’t really.

Some practical examples of this have been seen in the threshold tests I’ve performed with the panel regarding diacetyl. Some panelist’s thresholds are down below 30ppb, while others are well over 100ppb, and there are even 1 or 2 who may be totally anosmic to it (meaning they have no ability to detect it at any concentration). Training a panel to be good diacetyl tasters can be tricky since finding a concentration of diacetyl for a flavor standard that is appropriate for the whole panel is pretty much impossible.

Another example comes from the flavor standard “indole”, which has been known to elicit a floral jasmine-like aroma for a certain portion of the population, while the rest of the population smells fecal material. That part is interesting enough, but what’s even more so is that, for me, I can smell it both ways. Like an optical illusion, I can “flip” my brain’s interpretation of this aroma back and forth at will. It’s really an interesting experience to be smelling a nice flowery flavor standard one second, then in the next second your nose is full of poop.

PS: Indole arises in fermentations which have become contaminated by coliform bacteria (those usually associated with sewage and waste-water), and tends to be most common when adjunct sugars are used which are themselves contaminated.

Olfaction: Does the key still fit the lock?

Welcome back, Beer Readers! I’ll kick off 2011 with a brief [read: "half-assed"] discussion about the current level of understanding about how smell works.

Frankly, the sensation of smell is poorly understood. Specifically, the uncertainty is focused on how the receptors are stimulated by the odorant; the actual mechanisms behind how the resulting signal is carried to the brain is fairly well established (we’ll discuss gustducin and G-protein-coupled receptors more in the future).

For many years, olfaction has been described as a receptor-based system with aromatic molecules stimulating specific receptors in the olfactory bulb. This system has been called the “lock and key” model, since each receptor responds to only one “key” molecule. In this model, the differences in size and shape of a molecule is what allows the receptors to differentiate between odorants. There are some shortcomings in this model, however. Some molecules which are very similar in size and shape can have startlingly different aromas. Also, if one receptor matches one odorant, then how is it that can we identify many thousands of individual aromas when the human genome only has 350 genes which code for olfactory receptors? [By comparison, mice have 900 olfactory receptor genes which code for about 1200 individual receptors; or about 1200 different aromas, in the lock and key model.]

New research (and by “new” I mean within the last 15 years) descibes a much more complex picture of what is going on, and some follow-up research demonstrates that this new model has some real potential. What the new model posits is that, when the odorant molecule binds to the receptor, inelastic electron tunneling takes place where an electron is transferred from the from the donor molecule to the receptor, in a non-redox process (it can do this due to its ability to act like both a wave and a particle). This “activates” the receptor and allows it to “read” the vibrational energy within the odorant molecule. These vibrations can apparently vary rather significantly due to very slight changes in the structure of the molecule, which agrees with the observations that similar molecules can show different characteristic aromas. This could theoretically imply that a single receptor could might be able to associate with a number of different molecules, each one being seen as unique due to the differing amounts of vibrational energy they carry. But this quantum physics stuff starts to get a bit over my head (I’m more of a chemist), so I’ll just let this other WordPress blog post from 12/2006 describe this research.

I just love it when we find out that things are far more interesting, complex, and nuanced than we previously thought. It just re-affirms that we can’t become complacent about our level of understanding of the world, since you never know when the apple cart will be upturned and years of scientific understanding need to be re-assessed.

Happy New Year, hope your holidays went well, and see you next time! Prost!

Taste vs. Flavor: A retronasal excursion

So, when we talk about what a food or drink “tastes like”, it’s pretty common to get confused about the terminology.  You may hear someone say that something tastes “fruity” or “rancid” or whatever.  What they are actually discussing is how the food smells.  As we discussed already, “taste” applies only to the basic tastes. Everything else, apart from the various tactile sensations, is aroma. Combine the taste, the aroma, and the mouthfeel and you’re now talking about the overall flavor of the substance.

Here’s an exercise for you to try to drive home this point:

Eat or drink something while your nose is plugged.  What I like to use is a piece of gum or a mint candy or something. It might be tricky to swallow like this, but it’s possible.  So while your nose is plugged, what are you sensing?  Sweetness, sourness, saltiness, bitterness, temperature, texture, etc.  It’s all just taste and mouthfeel, right?  No aroma.    Now, unplug your nose and breath out through it.  NOW we’re in flavor country, eh? This aroma that you smell while food or drink is in your mouth is called “retronasal aroma” (backwards nose). It is distinct from “orthonasal aroma” (straight nose) which is sensed when you put your face over the food and smell normally through the front of the nose.

So apparently, the majority of food and beverage flavor is perceived by your nose.  What’s happening is, as the substance is in your mouth, it’s warming up.  This warming action allows the volatile aroma compounds to leave the food and enter the air in your mouth and sinus.  Also, the surface area of the food is increasing as you chew it and spread it around your mouth, which also allows more volatilization of flavors.  Other things might be happening as well, like bursting carbonation bubbles carrying even more flavors out of the beverage.  All these things are causing aromas to become “airborne” which allows them to be carried into your sinus (via the back of the mouth/throat). This retronasal method leads to distinct differences in the aroma of your food compared to the orthonasal method, since with the orthonasal method the warming and the agitation of the sample are considerably less. It’s not uncommon for the flavor profile of a food or beverage smelled retronasally to be quite unique from the same product smelled orthonasally, as certain compounds may not be volatile enough in the glass to be detected; they may need to be warmed and agitated to be detected at above-threshold levels. This demonstrates the importance of smelling AND tasting the product before you try to describe it.

Here is a diagram showing a cross-section of the human head, where you can see how the back of the throat is connected to the back of the sinus cavity.  This is where the retronasal aromas access the olfactory bulb at the top of the sinus (essentially the bottom of the brain) which houses the various receptors responsible for detecting aromas.

Cross section of mouth and sinus, showing how retronasal aromas access olfactory bulb.

So now that we understand how taste, aroma, and flavor are all related, we can use the correct terminology when we discuss our sensations and assess our beers with proper diligence.