How many identifiable aromas in a wine – the science

This is the second post in a series that looks at the number of aromas we can detect in a wine. My first post explained that many tasters claim to be able to identify several aromas in the same wine, while scientific research has shown that we are incapable of identifying more than four. Here I will explain more precisely how the research was carried out, and what it found.

The research was carried out by David G Laing and co-workers in the 1980s and 90s. As far as I know it has not been replicated in other laboratories, but as will become clear the experiments were effectively repeated in the same laboratory, and as far as I know the results are not controversial. They are, for example, described in Avery Gilbert’s book What the Nose Knows without being questioned.

In Laing’s first published work on this subject[1], mixtures of odourants were delivered to the noses of the subjects in vapour form through a duct 150cm long and 55cm in diameter, and the subjects were asked to identify the odours present. Each of the 7 odourants was a single chemical compound with a distinctive smell, and introduced to the subjects under its everyday name: vinegar, almond, spearmint, fruity, cloves, orange or camphor. Odourant concentrations were chosen to be moderately strong perceptually, and roughly equally strong for all odours individually. The odourants and were also known to be identifiable in binary mixtures in the chosen concentrations. The mixtures were created in vapour form for delivery to the subjects’ noses. Vapour, rather than liquid, mixing was chosen to reduce the possibility that the odourants would react chemically. It seems to me that all reasonable steps were taken to give subjects the best possible chance of identifying the odours.

The subjects were first allowed to familiarise themselves with the individual odours for several minutes. Then they were given mixtures that varied in terms of the odourants used and the number present, and asked to identify the odours in the mixture. The results are summarized in the figure below[1], which is the basis for the assertion that no more than 4 odours can be identified.laing_1989A few possible reasons for the low number of identifiable odours spring to mind: maybe the subjects were not skilled enough, or maybe the odours chosen were particularly difficult to identify. The investigation of those two possibilities was the subject of two further studies [2, 3], which were based on the same experimental setup.

To determine the effect of training and experience[2], two different sets of subjects were used: experts, and trained non-experts. The non-experts were trained over the course of 5 days, and on day 5  they were tested to ensure they could reliably identify all 7 odours when presented individually. The other group were expert perfumers and flavourists; they were “highly familiar with the test odourants, had daily experience with odour discrimination, and had a prerequisite before entering their respective professions of an excellent ability to discriminate and identify odours”. The experts and trained non-experts performed slightly better than the subjects in the initial study, with the experts being the most competent, but nevertheless the number of correct judgements still dropped to negligible levels when more than 4 odourants were presented.

The next study[3] looked at the importance of the type of odours used in the mixtures. A panel of 10 perfumers and flavourists selected two sets of 8 single compound odourants: good and poor blenders. The poor blenders were judged to be perceptually very different, and thus easier to identify in mixtures than good blenders. The common names of the good blenders were rose, musky, cinnamon, coconut, fruity, orange, burnt caramel and almond, while the poor blenders were bad breath, mushroom, cut grass, Dencorub, garlic, antiseptic, aeroplane glue and mandarin. The results were as suspected in the sense that the poor blenders were easier to identify. However, the differences were not large, and for 5 or more poor-blender odourants the number of correct identifications was still very low indeed.

The fourth study[4] brought the experiments one step closer to the reality of wine. Here, none of the odourants were single chemical compounds, but complex mixes of chemicals usually identified as a single odour: smoky, strawberry, lavender, kerosene, rose, honey, cheese and chocolate. Again, the results were similar to those of earlier studies, suggesting that we identify the smell of familiar objects as a single gestalt odour, even if multiple chemical compounds are involved in creating it.

In the last article of Laing’s I will discuss here[5], subjects were trained to identify the test odours, and then required to detect a single highly familiar odorant in stimuli consisting of one, four, eight, twelve, and sixteen odorants by using a selective-attention procedure. Identification fell to chance level when sixteen odorants were present. Unfortunately I only have access to the abstract of this article, but I presume that the important distinction between this and earlier studies is that the subjects were attending only to one odour, and that the odour was highly familiar. It seems that it was those factors that enabled some people to identify an individual odour in blends of twelve, which is a big improvement on the limit of 4 found in earlier studies.

For now, I shall let you draw your own conclusion on the applicability of these results to wine tasting notes.  I will return to that subject eventually, but in my next post I should like to take a closer look at how wine tasters arrive at long lists of aromas that seemingly break Laing’s four odour limit. In the meantime, if you found this blog post interesting you might also like to take a look at this one on the subject of olfactory white.

[1] Laing, D. G., and Francis, G. W. (1989). The capacity of humans to identify odors in mixtures. Physiology & Behavior, 46(5), 809–814.

[2] Livermore, A., and Laing, D. G. (1996). Influence of training and experience on the perception of multicomponent odor mixtures. Journal of Experimental Psychology Human Perception and Performance, 22(2), 267–277.

[3] Livermore, A. and Laing, D. G. (1998). The influence of odor type on the discrimination and identification of odorants in multicomponent odor mixtures. Physiology and Behavior 65 (2): 311– 320.

[4] Livermore, A. and Laing, D. G. (1998). The influence of chemical complexity on the perception of multicomponent odor mixtures. Perception and Psychophysics, 60 (4): 650– 661.

[5] Jinks, A., and Laing, D. G. (1999). A limit in the processing of components in odour mixtures. Perception, 28(3), 395–404.

How many identifiable aromas in a wine – the dilemma

Tasting notes with flowery language and long lists of descriptors divide opinion: Many wine geeks seem to expect them, and writers oblige, but on the other hand the wine-drinker-in the-street, when not ignoring them completely, will probably dismiss them as nonsense. Personally, I look at them quizzically, and ask myself if they are really communicating anything of value. There are a number of contentious issues in tasting note style and content, but in this and the next few blog posts I want to tackle just one: the number of aromas mentioned.

By aroma I mean something that is detected by the nose. It can be detected either ortho-nasally, by sniffing; or retro-nasally, through a passage between the back of the mouth and the nose. Because retro-nasal detection occurs when food or drink is in the mouth, most people get a strong but false impression that it is the tongue doing the sensing. Examples of aromas are orange, apple, vanilla, chocolate and coffee, as opposed to other non-aroma sensations like sweet, salt, acid and bitter, which are detected by the tongue.

The problem with the number of aromas in some tasting notes is that a series of experiments performed in the 1980s and 90s showed that people are incapable of identifying more than four in a mixture. So how can tasting notes meaningfully refer to more than four? For example, a tasting note taken from International Wine Cellar, lists ten aromas by my counting: fresh fruit aromatics of mandarin orange, black raspberry and grilled watermelon spring from the glass. On the palate, pretty nuances of rose petal, gardenia and oolong tea mingle with herbal notes of sandalwood, star anise, fresh thyme and fennel seed. So what is happening here? Was there a problem with the experiments that were performed? Or, after the first four most prominent aromas mentioned in the tasting note, are we merely reading the results of an overactive imagination?

I shall be weighing the evidence for these alternatives over the next few blog posts, starting with an examination of the science. I’m trying to keep an open mind, but am currently leaning a little in the direction of the scientific research.

Glass shape, and how wine tastes

Around a month ago there was a flurry of interest in the wine world because new research had supposedly proved that wine glass shape is important for how wine tastes.  See for example the Open Culture and National Geographic articles. Being naturally sceptical, I dug out the abstract for the paper describing the research, and then the paper itself.  In brief, the paper proves no such thing, and doesn’t claim to either.  However, if you are intrigued and want to know what the paper actually relates to, read on…


It describes a novel technique for measuring the presence of ethanol vapour, and the authors used the technique to measure ethanol at the mouths of various glasses containing wine. Note that a) they measured ethanol vapour concentrations and b) the measurements were made on vertically standing glasses, presumably ones that had been standing for some time to allow the vapour patterns to stabilise.  Sadly for wine lovers, they did not measure the concentrations of the interesting aromatic compounds that give wines their smell and flavour, and they did not measure anything from a glass that had being swirled a little and inclined towards the mouth.

So what possible interest could this be to wine drinkers?  Very little I would suggest, notwithstanding some remarks made in the National Geographic article about alcohol suppressing flavours, the questionable evidence for which seems to relate to alcohol in solution anyway, not the vapour form. However, there was also an intriguing comment by the original authors referring to the ring-shaped alcohol pattern in the mouth of the Cabernet Sauvignon glass: This phenomenon allows us to smell the aroma of the wine in the center of the glass at a lower alcohol concentration. Accordingly, the shape of the wine glass has a very sophisticated and functional design for tasting and enjoying the aroma of wine.  A strange comment I thought, which came out of the blue and with little explanation or justification.  It could be construed as a nod to Riedel who provided “technical assistance and advice”, but I wouldn’t dream of being so cynical.

Neurogastronomy – book review

neurogastronomyThe full title of the book is Neurogastronomy: How the Brain Creates Flavor and Why It Matters, it is by Gordon M Shepherd, and the Amazon price is currently around £17.

The first thing I would point out is that this book is written by an expert in the field, and that sets the tone of the book.  There is no breathless prose interspersed with misunderstandings, which you can get when a journalist presents a subject,  but the down-side is that some of the language and concepts may be beyond the intelligent layperson, who is presumably the intended reader.  They were certainly beyond me.  That is not to say I got nothing out of the book.  Once I had learned to not get to hung up on the tricky bits, I found it interesting and rewarding.

Shepherd’s main theme is that a lot of what we call flavour comes from the sense of smell, and that we humans are actually a lot better at smelling things than many give us credit for.  Other animals may be better at detecting low concentrations of air-borne smells, but the human anatomy is better geared up for detecting smells retro-nasally, i.e. through the passage between the back of our nose and the mouth.  It is the retro-nasal smells that help create the flavour of our food and drink.  The other big advantage humans have when it comes to our sense of smell is brain size, which allows us to better use the information we get from the nose.

The book largely deals with the “how the brain create flavour” bit of its subtitle, and does that well.  I found it especially intriguing that smell and taste receptors are connected to the brain cortex via completely different routes, finish up in parts of the cortex that are greatly separated, and yet the brain still manages to integrate these senses to create a unified impression of flavour.  From this book, it is clear to me that we know so much about how this works, and how the process is affected by genetic differences, that it is impossible to continue to argue that flavour is a property of the food (or wine) put into our mouth.  And yet Charles Spence, in his detailed review of the same book, thinks it is still up for discussion.  Do read that review, though – I have great respect for his writing.

I was particularly looking forward to the “why it matters” bit.  But I was disappointed.  I was told how important flavour is, and how craving for food involves some (but not all) bits of the brain that have to do with drug addiction.  But I did not see any support for the claim that neurogastronomy should inform policy making.  Certainly a good case was made for the importance of flavour in determining how we eat, that that could be demonstrated without reference to neurogastronomy.

Wine was referred to a few times in the book, but for me the most relevant observation was that smell objects are represented in the brain in a very similar way to faces.  In fact Shepherd is more precise – he likens them pointillist images of faces, where each type of odour receptor represents a dot, but seen at a distance the dots combine to create smell equivalents of colour and shade.  He goes on to observe that familiar smells, like faces, are easy to recognise but very difficult to describe.

Finally, there was a suggestion supported by limited experiments that the more you are exposed to a smell in the long term, the more sensitive to it you become.  So if you want to improve your sensitivity to the different aromas in wine, the answer seems to be to increase your exposure to them.  Even if that fails to improve your sensitivity, it must help recognition mustn’t it?  It works for faces at least.

Postmodern Winemaking – book review


This is a review of Postmodern Winemaking by Clark Smith.  As I write, according to Amazon in the UK the book has not been released and has a price of £24.95, while via you can get it from partners for various prices from $68.04 to $368.08!  I am not sure if it now is properly released or not, but I got my copy from The Book Depository for just under £19.

I did not get on well with this book at all.  I understand it is largely based on a collection of articles written for various publications, and my goodness it shows.  There is seemingly endless repetition, and many pointers between chapters constitute a vain attempt to make everything seem coherent. If Clark had taken the time to explain everything properly once, the ideas would be a whole lot clearer and it would be a much shorter book.

I am not the sort of person that is intimidated by science – I studied it at university – but I could not make much sense of most of Clark’s explanations, and simply repeating the same things many times helps not a jot.  Annoyingly,  so many times he prefaced an explanation with the proviso that not everything has been confirmed by science, without saying where speculation takes over from more solid ground.

He also seems to miss the main point about science.  It is not there to dot the Is and cross the Ts of his great ideas, and those of other great visionaries like Rudolf Steiner, giving them a stamp of white-coated approval.  The scientific method is actually little other than common sense for many people.  On the other hand, anecdotal evidence and speculation has proved so many times to be false.

The style is that of a preacher, or a seller of snake-oil, and make no mistake he is selling – both himself as consultant, and his wines.  The book is full of poor analogies endlessly repeated.  The one that wound me up most was the comparison of micro-oxygenation with homeopathy.  Sure, a little oxygen at the right time in winemaking may prevent oxidation at a later stage.  But that is to miss the point about homeopathy, where there is probably nothing of the active ingredient in the remedy.  With MOx you do actually add some oxygen.

Despite my complaints, I did learn something about modern (I still refuse to use the word postmodern in this context) winemaking techniques – just not as much as I had hoped.  I also very much felt myself cheering along when he was encouraging winemakers to be more open about how they make wine, and stop feeding journalists with what they and their marketing people think punters want to hear.  If they really think these techniques improve wines, they should have the courage of their convictions.  The same applies to older practices like chaptalisation.

Do his ideas work?  I have not a clue.  The book certainly expressed Clark Smith’s points of view, but the guy is clearly controversial and I am not convinced from the evidence presented.  However, I am prepared to keep an open mind.

For more views, and more details on the content of the  book, follow these links:

The Academic Wino

Wine Wisdom

Wine Searcher

NY Journal of Books

Notes from the Winemaker

Fooling the experts?

An article published last week in the Observer, Wine-tasting: it’s junk science, has proved controversial.  As it covers a subject that interests me greatly – how we perceive, describe and rate wines – I wanted to post about it here immediately, but I was not sure how to start.

Perhaps the best way is to point out that the article itself refers to the work of others, and it represents a fair summary of that work.  If you don’t like the results, read the original studies, and criticise them from a position of knowledge, but do not dismiss them out of hand.  As far as I can tell, with the exception of the widely reported Wisemann study, they are sound pieces of work.

The second thing I would say is that the article’s headline misses the point completely.  Winetasting is not junk science.  It is not any sort of science.  It’s…  well, it’s tasting wine: smelling it, putting it into your mouth, and attending to what you perceive.  Punters, individuals and businesses, do it all the time and base their buying decisions on it.

Tasting itself is not problematic.  The content of the article is about how reliable experts are at describing and rating what they taste.  To be reliable, each individual expert needs to be consistent, and also different experts needs to be able to form a consensus with other people, ideally other experts.  To me it is clear that the studies show there is little reliability.

But that raises another issue: who are these people (who I am calling experts) that are unreliable?  They are different in the various studies.  Judges at shows are typically taken from the wine trade, and can be a mixed bunch.  In the Goldstein study, those who had any form of wines education were deemed to be expert.  And university studies often use oenology students as subjects – these presumably have attended courses on tasting.  Few of the subjects would be Masters of Wine, Master Sommeliers, or even enthusiasts who take part in blind tasting competitions. Were they to be made the subject to research, who knows what the results would be?  Not too dissimilar from the existing studies I suspect.

I do not wish to associate myself with the tone of many of the article comments that glory in the stupidity of the experts and wine snobs alike, but I can see that they have a point.  A lot of the language used to describe wine is rather ridiculous.   Some is designed to elevate the status of the writer rather than to communicate, and other descriptions are simply invented to sell the wine.  Couple that with demonstrable expert reliability problems, and I can absolutely understand the substance of their complaints.

I think the premium end of the wine trade has a big problem in communicating to the general public, in the UK at least.  The answer is not for experts to get defensive about their abilities, and hurl criticism back to punters saying that they are stupid for continuing to buy cheap wine from their supermarkets and that they need to take courses to appreciate wine.  We really do need to move on from trading insults.  In my opinion, as evidenced by his recent book, Eric Asimov gets the tone just about right in his unassuming modesty and willingness to engage with the public.

Update: Just in case you are interested, here are another couple of responses to the article, from Fiona Beckett, Tim Atkin and Victoria Moore.

Order effects, and linguistic fluency

I thought that subject line would get your attention 🙂

In you have an hour or so to spare, take a look at this lecture by Antonia Mantonakis entitled “Does a wine’s name influence consumer taste perception?”  It also covers other influences on taste perception that have nothing to do with the wine itself.

So, to my list of factors that explain why wine tastes the way it does, it seems we can add the following two:

  1. Order effects
    I mentioned in my earlier list that the previous wine tasted affects how the current one is perceived, but Antonia found more general order effects.  In short sequences of  up to 3 wines, consumers show a preference for the first one.    But for longer sequences, up to 5 wines, the last one is preferred.   This research is briefly referred to in the video, but I could not find a publicly accessible research article to link to.
  2. Linguistic fluency
    Two winery names were made up, one of which was easier to pronounce than the other, but in other respects they were the same. In contrast to how linguistic fluency (ease of reading and pronunciation) affects perception of more basic consumer goods, it was found that a wine associated with the less fluent name tasted better.   More details in the video and this article.  I am sure I have heard it said many times that wines with simple names have an advantage in the market, but maybe that idea came about by the invalid extension of results from other product categories.

I’d like to emphasise that these results refer to reported perceptions.  There is admittedly the issue of whether people say what they really think about a wine, or say what they think they should be saying.  It might even vary from experiment to experiment, but MR scan evidence and a clever experimental design suggest that people at least sometimes say what they really think they perceive.

The final thing I would like to comment on is perhaps the most surprising, at least for those who fancy themselves as wine experts. The subjects in the experiments mentioned in the two points listed above were divided into two categories: those who knew more about wine, and those who knew less. Guess which group was more influenced by the order and linguistic fluency. It was the more knowledgable one!

Wine scoring

Debating the merits of scoring is a well-worn topic on wine blogs and forums, but this nicely argued contribution on John M Kelly’s blog “notes from the winemaker” offers an original perspective. Do read it for yourself, but basically John describes the lengths it would be necessary to go to in order to make an objective assessment of a wine.  Of course, no critic works like this, and their scores are essentially subjective.

After reading it, something else occurred to me.  If wines were scored with the rigour described in John’s blog post, the scores would still most likely be meaningless to the consumer, possibly more so than the scores of today’s critics.  Why?  Because all the factors that are so important in drinking and enjoying wine are removed in order to get a reliable assessment, and no one actually drinks wine in laboratory conditions.  An even more fundamental objection lies in the definition of what makes one wine better than another.  It is one thing to make that definition explicit as suggested by John, but it would be impossible to get one that everybody would agree with.

To the extent that there is any agreement at all about what makes a good wine, the most common definition you hear these days is “one that has a sense of place”.  What procedure would you use to measure that?

Temperature variation in wine cellars

The above diagram is taken from p303 of David MacKay’s book Sustainable Energy – without the hot air.  It shows how temperature in the ground varies with depth and time of year if the surface temperature varies as a sine function with a minimum of 3°C and maximum of 20ºC.  You can see the surface variation by reading off the temperatures from the horizontal slice through the diagram at depth 0.  Further into the ground, at depth 2 for example, you can see that the temperature is colder, varies in the range 10-13ºC, and the minimum temperature lags behind the surface temperature by about 5 months.  More rapid temperature variations, within a day and from day to day, are ignored, but these would be very small at almost any depth.  The correspondence between depths 0, 1, 2, 3 and depths in meters depends on the ground material; examples from MacKay are given in the table below.

Granite Damp sandy soils
or concrete
Dry or peaty soils
Depth 0 0.0m 0.0m 0.0m
Depth 1 3.0m 2.6m 1.3m
Depth 2 6.0m 5.2m 2.6m
Depth 3 9.0m 7.8m 3.9m

Of course, this would be a good predictor of temperature variations in your wine only if you had a few bottle buried outside, and perhaps in some commercial cellars.  Domestic cellars are usually directly below houses, and thus have surface temperatures that are both higher and more constant than those assumed in the diagram, and there are not metres of earth or rock between the cellar and the house.  But even then, the diagram does perhaps give some idea of the cooling effect from cellar walls.  If you are keener than me you could try doing calculations more relevant to wine cellars – MacKay gives you some equations you could use at a starting point.  Or you could just put a thermometer in your cellar.

Another wine application of these calculations would be to predict the temperature of vine roots at various depths.  I have no idea how important root temperature is to the vine, but if it is you now know where to get the equations.

Finally, a big thank you to David MacKay for allowing his material to be used under a Creative Commons licence.  See the website for details, but amongst other things it allows you to download the book free of charge.  I admit I have by no means read it all, but it looks well written and very interesting.