Thursday, 28 November 2013

Colour me .... minty

A recent article in the UK’s The Guardian newspaper (Friday, 25 October 2013; was a potent reminder of the power of expectations in determining food likes and dislikes. The paper sent a camera crew armed with samples of a new flavour of Pringles potato crisps to observe the reactions of the public in a “taste test”. The facial expressions shown in response to the new flavour are unambiguous, and almost all highly negative. Why? Well, it wasn’t that the flavor itself was vile – no earwax or stale fish – but merely an unexpected …. mint chocolate! One participant, close to disgust, even commented that this was his favourite flavour, but just not in a potato crisp.

This demonstration reflects very well how expectations are set up by past experiences, in particular, experiences with combinations of sensory properties. This includes not just tastes, odours and textures, but especially those qualities – visual cues such as shape and colour – that set up a template of what something is about to taste like. In the case of potato crisps, this might include flavours such as salty potato (ie., plain), “chicken”, vinegar or even more exotic combinations such as lime and pepper or chilli - savoury flavours all. But what induces the extreme reactions to what is, after all, a crispy, choc-mint treat? One possible explanation lies in considering that the predictability of a food’s flavour, based on external, visual cues (at least for visually-dominated species like us and the birds) is an important key to survival in the wild. In this sense, violations of expectations are a warning signal and like many warning signals involving food, they are underpinned by an unacceptable taste experience that is likely to inhibit eating.

This is a cognitive component to our taste experience. And it essentially means that any combination of colours, odours, textures, tastes can be acceptable if together they are consistent with one another. For this reason, for example, we can accept white wines that smell like cat’s pee or cut grass or caramel or petrol.

Clearly a food’s colour provides us with the key information we need to make a decision about whether to sample further by smelling or tasting. Green bananas, yellow lettuce, and grey meat tend to be diverted before they get close to the mouth. But the next payage on this alimentary motorway is our sense of smell which, at least when we are sniffing, can provide us with information about food at a distance, just as our vision does. This means not only that our senses of smell and vision are used to confirm the information provided by each other, but that particular qualities in each sense (odours; colours) become associated with one another. Hence, repeated pairings of specific qualities in each sense becomes over time a joint signal for the presence of something that can be eaten. Such learned congruency (belongingness) of different sensory signals has a parallel in the way in which specific tastes and odours combine as familiar food flavours and producing, as a results of this integration, odours that smell like tastes [1].

How colour combines with other food sensory signals perceptually or cognitively has been uncertain, although colour effects have received increased scrutiny recently (see for example, [2]). Does colour ‘merely’ act to set up expectations, or should we consider food/beverage colours as an integral aspect of the overall flavour? A just published review [3] by Debra Zellner (Montclair State University, USA) provides an overview, and explanatory model, of colour-odour interactions. Zellner draws together the various findings on odor discrimination and intensity, as well as odour pleasantness, and argues for perceptual – as opposed to response bias – effects of colour on odour in each case. In essence, she is saying that colour can influence odour in much the same way as odours can enhance taste intensity, and for the same associative learning reasons.

Zellner leaves open the possibility of innate (unlearned) responses to odour-colour combinations, but this seems unlikely. Perceptual learning is a flexible process precisely because environmental conditions may dictate the combinations that could signal something edible. Hence, appropriate colour/odour combinations for foods would be expected to vary cross-culturally, and this has been shown in a recent study involving varying drink flavour and colours [4]. One could imagine, however, that colour intensity and odour strength might be intrinsically linked, but this may be an example only of our more general ability to equate intensities across different sensory modalities.

One reason that there has been little consensus on how colour might influence odour perception is because of apparent inconsistencies in these interactions. Thus, while there is evidence that colour can enhance sniffed odour intensity, there are also findings that the intensity of ‘tasted’ odours – flavours – are suppressed by the presence of colour. On the face of it, this seems a bizarre finding. How could an unperceived quality (the colour in the mouth) produce any effect at all on the flavour? To account for this, Zellner invokes the idea of a contrast between the sniffed and the tasted odour. So, if the odour/colour combination is first experienced by sniffing/seeing, then an enhanced odour intensity is produced. However, once the odour source is in the mouth, then there is no further input from the colour, and the intensity is a function of the odour only. The suppression is thus relative, a comparison of the odour enhanced by colour and the same odour with the enhancement suddenly removed once the odour source is in the mouth.

In the light of the Pringles demonstration, it is not surprising that when colour and odour do not match, then the odour/flavour tends to be judged less favourably. An expected combination is also a familiar one that carries with it an implicit recognition that previous experiences are associated with a positive outcome. As with odour/taste combinations, repeated exposure not only produces an integrated perception of a flavour but also has hedonic consequences. Even if an odour/taste combination is not initially liked, the effects of exposure, and the positive effects of the nutrients in the food, produces a liked flavour over repeated pairings. 

Intriguingly, colour/odour pairings might also generate an influence in the opposite direction – that is, odours might conceivably enhance colours. While if shown to be the case, this would no doubt have some food applications, those applications that immediately spring to mind relate to effects that could be produced environmentally or artistically. Perhaps, too, this could provide a perfect opportunity for aromatherapists and colour therapists to combine their ‘talents’, hopefully saving their poor consumers some money.


1. Prescott, J., Multimodal chemosensory interactions and perception of flavor, in Frontiers in the Neural Bases of Multisensory Processes. 2012, CRC Press. p. 691-704.
2. Dematte, M.L., D. Sanabria, and C. Spence, Cross-modal associations between odors and colors. Chem. Senses, 2006. 31: p. 531-538.
3. Zellner, D.A., Color–Odor Interactions: A Review and Model. Chemosensory Perception, 2013. 6(4): p. 155-169.
4. Shankar, M.U., C.A. Levitan, and C. Spence, Grape expectations: the role of cognitive influences in color-flavor interactions. Conscious Cogn, 2010. 19(1): p. 380-90.

Friday, 11 October 2013

Feeling all emotional

Leaving aside issues of nutrition, we usually judge a food by how much we like its flavour. But what is ‘like’? Ask a social psychologist and, after prolonged qualifications, they will probably tell you that ‘like’ is an attitude or a positive disposition towards something. So, if you wish to compare two foods in terms of liking or acceptability or preference, then degrees of positive disposition are what we are after. This doesn't sound very much like pure pleasure of the type that food can produce and yet ratings of liking are what are used by food companies to discover how consumers respond to foods and even to make decisions about whether or not a particular product should be launched into the marketplace.

Ratings of liking are thus a proxy for an emotion – pleasure – and for a behavior, food choice. This would be fine if we could be sure that ‘liking’ was a good proxy for either, but there is little evidence that this is the case. Here’s the problem. There is a substantial body of research and practical experience showing that liking ratings fail to predict later food choices. Very many reasons can be found to explain this, including the fact that rated samples are not representative of meals, that liking varies as a function of many variables – time of day, mood, and so on, and that choice is influenced by other variables apart from liking.

A relatively recent approach to this problem has been to ask if we are measuring the right thing. Are positive dispositions the sort of thing that are likely to reveal the next big product? I have posted previously about comfort and wanting. We recognize that a search for comfort is a particular feeling that will direct us towards specific types of foods, at least some of the time. Wanting, too, is a strong motivator that might underlie actual choices, irrespective of degree of liking. Of course, there are a multitude of emotions that we could measure, some of them perhaps quite important to us. Clinical psychologists and psychiatrists have been using standardized measures of emotion for some time, but the emphasis is unsurprisingly on negative emotions that are unlikely to be elicited by eating in most of us. 

Compiling lists of independent emotional terms that might be more related to foods can of course be done and there are examples in the recent literature (see for example [1]). There is certainly evidence that rated emotions do discriminate between products, and perhaps in some cases better than liking ratings [2]. But the issues to be addressed are many. Thus, how do we know that a food-elicited emotion is not mediated by the pleasure given by the food (as reflected by ‘liking’) rather than being a direct result of the food experience? This would be consistent with a great deal of research showing that pleasant stimuli of all kinds produce positive moods, which in turn might be described using words such as ‘cheerful’, ‘energetic’ or ‘friendly’ – all terms that have been used in emotion questionnaires.

Which brings us to another important issue: just how many emotions are there and how do we decide which ones to measure? On the basis of detailed cross-cultural comparisons, Ekman [3] for example has argued for the universality of a small number of emotions – happiness, anger, disgust, fear, sadness and surprise – and their associated facial expressions. If this is true, then it may be that your ‘cheerful’ is the same as my ‘friendly’, and that we actually both mean ‘happy’. In other words, perhaps these terms are all highly correlated with something called ‘positivity’. Searching for such key descriptors is not unlike the search for non-redundant terms in describing the sensory properties of products. But it is a more complex task to determine if a consumer’s rating of an emotion as irrelevant to their food experience represents actual lack of feeling or a poor fit between the word and what is actually felt. And that’s even without considering such seemingly bizarre concepts as “guilty pleasure”.

An emotion, though, is not just an internal feeling that needs a label. William James raised the question over a century ago of whether the other aspects of emotions – physiological responses and facial expressions – might not actually be primary, in that they precede the subjective feeling. To paraphrase his argument, do we run from a bear because we are afraid or are we afraid because we run from the bear? If the latter (and see [4] for evidence of this), then either facial expressions or the physiological correlates of emotions might be more direct measures of responses to foods.

While measuring facial expressions could be considered a more objective means of getting directly at emotions because they can be objectively verified, it is not true that expressions are spontaneous. We all manage our expressions, masking or modulating them depending on the context (or culture) we are in – a skill that is evident even in 3 year olds. Moreover, just how finely are smiles/frowns gradated? More than a 9 point liking scale? In a recent study [5], automated readings of positive (happy), neutral and negative (angry, disgusted) emotions in response to juice samples tracked ratings on a 9-point hedonic scale quite closely. In fact, the facial readings were able to differentiate between the samples, but not to a degree better than the scale.

Measures of physiology in response to foods are at a similar state of progress. Food scientists are now in many ways tackling some of the same issues that William James did at the end of the 19th century. Psychologists have recognized for the past century that quite different emotions share common physiological traits – e.g., both fear and anger are associated with increased heart rate. Following James, later theories of emotion emphasized the role that cognitions – interpretations – had in determining which emotional quality was associated with particular physiological changes for a given context. This was compellingly shown in Schacter and Singer’s classic 1962 experiment on the role of expectations in emotions [6]. They showed that physiological arousal produced by an injection of epinephrine (adrenalin) could be interpreted as consistent with either anger or excitement, depending entirely on the context to which the subject was subsequently exposed. While there are good data showing that foods do elicit changes in physiology [7], once again the ability of these changes to predict food choice is unknown. In any case, the context in which the food is experienced is likely to be crucial.

My feeling is that there are a few years left in old liking scale yet. If we don’t receive sensory pleasure from a food, it is more than likely doomed to be a single purchase item; but the converse is not true. Liking therefore might best be seen as a measure that is necessary, but not sufficient, to predict food choices. The search is really for complementary measures that add some predictive power. The fact that emotion research has yet to add this tells us only that some key questions are in need of answers and that it is premature to expect successful applications without more basic research.


1. Cardello, A.V., et al., Measuring emotional responses to foods and food names using questionnaires. Food Qual Pref, 2012. 24: p. 243-250.
2. Ng, M., C. Chaya, and J. Hort, Beyond liking: Comparing the measurement of emotional response using EsSense Profile and consumer defined check-all-that-apply methodologies. Food Qual Pref, 2013. 28: p. 193-205.
3. Ekman, P. and W.V. Friesen, Constants across cultures in the face and emotions. J. Pers.Soc. Psychol., 1971. 17(2): p. 124-129.
4. Strack, F., L.L. Martin, and S. Stepper, Inhibiting and Facilitating Conditions of the Human Smile: A Nonobtrusive Test of the Facial Feedback Hypothesis. J Pers Soc Psychol, 1988. 54(5): p. 768-777.
5. Danner, L., et al., Make a face! Implicit and explicit measurement of facial expressions elicited by orange juices using face reading technology. Food Qual Pref, 2013 (in press).
6. Schachter, S. and J. Singer, Cognitive, Social, and Physiological Determinants of Emotional State. Psych Rev, 1962. 69: p. 379-399.
7. de Wijk, R.A., et al., Autonomic nervous system responses on and facial expressions to the sight, smell, and taste of liked and disliked foods. Food Qual Pref, 2012. 26: p. 196-203.

Friday, 23 August 2013

Implicit implications

How do you know what you know? Much of what we do and the decisions that we make are based on knowledge or attitudes that are accessed without conscious effort. Hence, driving a car would be impossible if we continuously needed to think about each step of the process. Experienced doctors are able to make snap decisions by ‘reading’ a patient and their health without going through an explicit mental checklist. It is all part of the process of the automation of perception and reaction that is characteristics of expertise.

Expertise comes in a variety of forms. In one sense, we are all experts regarding the products we use or consume. Food psychologist EP Koster has often made the point that we instantly know when a food company has tampered with our favourite marmalade, even if we are not sure exactly what has changed. Experimentally, too, this was shown in a study in which very small amounts of tastants (sweet, sour, bitter) were added to foods (cream cheese, orange juice, yoghurt) that had been sampled earlier in the day. Asked to compare the new versions with those they had consumed earlier, the participants were especially sensitive to any negative change produced by minimal increases in bitterness, even though it is unlikely that would have been able to articulate what exactly the change was [1]. In other words, they were retrieving implicit rather than explicit information.

In some cases, information is encoded implicitly in the first place, and our behavior and preferences can be shaped by experiences with stimuli that never entered conscious awareness. Thus, the ingenious study of the German recipients of formula milk to which vanilla had been added showed that these experiences were influential in determining a food choice (ketchup with or without a tiny amount of added vanilla) even 30 years later [2].

Consumer research of any kind is aimed at retrieving knowledge that is assumed to be at the consumer’s fingertips. But what if it isn’t? Social psychologists sometimes study phenomena in which an ‘honest’ answer can not be assumed. Thus, if asked questions about our own attitudes to other races, there is enormous internal pressure to conform to cultural norms, even if we know that the information won’t get further than the researcher’s computer. We do not like to admit even to ourselves that we have attitudes that would meet universal disapproval if voiced.

Consumer researchers sometimes have the same concerns, although this is more motivated by the fact that ratings of liking for, say, a new product is a poor predictor of how well that product will actually do in the marketplace. The rather illogical response is sometimes to blame the consumer: they are obviously stubbornly not revealing their true attitudes towards the product. One consequence is the search for “objective” measures of liking such as brain scanning - as though there was a blind alley between “the brain” and the mouth down which honest opinions get sent.

One approach to the problem of retrieving attitudes taken by social psychologists has been the development of the Implicit Association Test (IAT). This is based on the assumption, not that people’s responses are inherently dishonest, but that there may be attitudes that are not explicitly or consciously available or that are difficult to put into words. The technique works by exploiting the fact that responses to things that belong together (words; objects) are faster than when there is a disconnect between them. So, if I flashed up pairs of words on a screen and asked you to instantly press a key, your response to “mother + father” would be quicker than to “mother + sheep”. Now, as the social psychologists do, imagine if I flashed up the name of another race (you decide which!) plus either of the words ‘dumb’ or ‘smart’. Any difference in reaction times between these two words paired with the race would reveal attitudes without ever having to ask a question about racial beliefs.

As one example, I previously (Le topic du jour: Gout qui importe; December, 2012) reported the distinction between French and American consumers in their attitudes towards food tastiness and health, the results of an IAT study that compared responses to the terms “tasty” with “healthy” and “unhealthy”.

The pairings in the IAT do not need to be words but can also be visual images such as labels, people, places or events. For instance, the IAT was recently applied to examining the fit between marketing slogans and their associated products. Pairings of the words “gentle” and “powerful” with images of the bottles of different brands of mouthwash showed that consumers had internalized the marketing messages of each company. Responses to the mouthwash that marketed itself as gentle were fastest when the bottle image was paired with this label than when paired with “powerful”; conversely, the word “powerful” produced the faster reactions times when paired with the bottle of the other brand, again consistent with its marketing [3].

There are indications that measuring implicit responses is being increasingly recognized in sensory consumer science. At the recent Pangborn Symposium in Rio de Janeiro (see: several presentations focused on measures of implicit reactions to products, including the measurement of emotions – currently one of the current hot topics in sensory/consumers research – using the IAT. Other reported implicit measures included the measurement of facial responses, although the extent to which these might be consciously controlled is an important methodological issue.

One potential next step is to include product tasting with the IAT and assess the extent to which the product’s sensory and functional properties is congruent with the product image and concept. The final plenary talk at the 2013 Pangborn discussed the issue of fit between a product’s conceptual profile (essentially the set of associations and emotions that it evokes) and its sensory properties, noting that the degree of alignment of the two equates to whether or not a product ‘fit-to-brand’. The conclusion was that significant mismatch between a product’s conceptual profile and what it actually delivers to the consumer presents a serious risk that the product will fail [4].  


4. Thomson, D. The application of conceptual profiling in brand, product and packaging development. 10th Pangborn Sensory Science Symposium, Rio de Janeiro, Brasil, 11-15th August, 2013.

Friday, 26 July 2013

Absolutely love it! … relatively speaking

You can never go back. I had an opportunity recently to take a sip of a wine that I used to happily drink some … ok, many ….years ago. A sip was more than enough! The shame of it was that the amount of pleasure I can get from an excellent wine now is probably no greater than the pleasure that Chateau Chunder (ok, not that bad) gave me all those years ago. 

Pleasure is relative … not only to our current state of mind, but to recent experiences as well. In an excellent discussion of this phenomenon, Parducci [1] analysed the impact of recent experience on how happy we feel. How happy would you be to find $10 on the street? Let me ask you another question before you answer: are you just stepping out of your Ferrari or on your way to the unemployment office? Alternatively, imagine you find $20 on the street every day for a month ….. how do you feel if one day there’s only $10? In both cases, the context (your financial state or your recent experiences) provides the background that determines the degree of pleasure that you are likely to experience.

Our sensory experiences are not exempt from context effects either. Another balmy 19 C (66 F) day. Now, depending on where you live, you might agree with me or alternatively consider that it’s me who’s balmy. The fact is, I have given you a piece of information and an interpretation, but what is missing is to know where I am at present, and hence the season*. These extra details allow you to place both the information and my interpretation in context. Most of us at some time have eaten a dish that is just too hot (spicy). Part of this may be due to the physiological impact of recent chilli eating, or lack thereof. But mostly, it will be a mental comparison of the heat of the spicy dishes that you have had recently with what you are eating now [2].

Each of these examples show how any given sensory or emotional experiences occurs against a background of other similar recent experiences. From the perspective of wanting to measure sensory or hedonic experiences, context effects are not merely an interesting quirk – they are the main game. All human measurement is relative. Even a simple question of deciding whether or not you like a beverage is really a case of liking it “compared to what”. In evaluating consumer preferences for foods or beverages, the common scenario is that multiple samples – different brands or different versions of a product – are compared at each tasting session. In the less common situation, though, that a single product was rated for liking, we would expect that the point of comparison was the consumer’s prior, and especially recent, experiences with that class of product [3]. 

When multiple products are compared within the same evaluation session, the products are compared relative to one another. One consequence of the influence of context in ratings is that a given product can be given a low or a high liking rating entirely as a function of what other products are in the evaluation [4]. To take an obvious (and unrealistic) example, imagine that you are asked to rate your liking for different flavours of jelly-beans: orange, lime, blueberry, banana, and … tomato. The latter is obviously an odd sample (despite being a fruit) and is likely to be rated lower. Next, however, I ask you to rate your liking for the following jelly-bean flavours: spinach, brussel sprouts, potato, cabbage, and …. tomato. Here, I imagine that the tomato flavour would be a winner. 

It is crucial to understand the implications of context effects if consumer data are not to be misused. Many food companies have in the past, and to a lesser extent still today, relied on fixed acceptability ratings as criteria for action. For example, on the standard 9-point hedonic scale, a mean rating of 7 (representing “like moderately”) in consumer testing may be required to launch a product. Since any given number on a rating scale can only really be understood in relation to the ratings given other products, there is no validity to adopting such a value. Ironically, dogmatic reliance on such cutoff values is a key reason why there is resistance in industry to adopting new approaches to measurement. 

A key theoretical question about context effects is whether they reflect actual subjective experience or occur due to the way we use rating scales. One of the main explanations for context effects is Adaptation Level Theory which suggests that we adapt to the changing environment, establishing a reference level against which intensity/pleasure is judged [5]. This approach has many parallels to sensory adaptation (e.g, adapting to be able to see in a dark room) and leaves open the possibility that context alters experience. The Range-Frequency Theory on the other hand is a theory of how we use rating scales [6]. This theory suggests that when faced with the task of rating the intensity or pleasantness of a stimulus range (e.g., products varying along some dimension), we mentally divide the scale into equal intervals, and distribute the ratings over these intervals. Thus, context effects are due to the range of stimulus values and the frequency of each value.   

There are certainly data to support range-frequency theory but clearly I do not need a rating scale to judge whether or not I am happy – to greater or lesser degrees - at finding $20 on the street. That’s an unusual, and positive event. Once this has happened 20 times though, it becomes the norm against which daily events are judged. Tomorrow’s $20 may not even evoke a smile, and $10 in its place may even leave me a little annoyed.

Food consumers, too, experience the same phenomenon. And this may give rise to an interesting paradox in which favourite foods – as reflected in recent, repeat consumption – do not evoke particularly strong positive emotions. A relatively new field in consumer research is the measurement of a wider range of emotions beyond liking. Understanding the impact of context effects in such measures is clearly an important step before their widespread application. Moreover, while sensory acceptability is crucial, there are other reasons why we consume. These include feeling of comfort or security. Perhaps these motivations are exempt from the effects of context, but as yet we don’t know.

[ * The missing bit is ‘Sydney in winter’ and, though making you envious is far from my mind, I need to point out that, yes, it’s often 19 C]


1. Parducci, A., Happiness, Pleasure and Judgment, 1995, New Jersey: Lawrence Erlbaum.
2. Stevenson, R.J. and J. Prescott, The Effects of Prior Experience with Capsaicin on Ratings of Its Burn. Chem. Senses, 1994. 19(6): p. 651-656.
3. Walter, F. and R.A. Boakes, Long-term range effects in hedonic ratings. Food Qual. Pref., 2009. 20: p. 440-449.
4. Schifferstein, H.N.J., Contextual shifts in hedonic judgments. J. Sens. Stud., 1995. 10: p. 381-392.
5. Helson, H., Adaptation-level as frame of reference for prediction of psychophysical data. Am J Psychol, 1947. 60(1): p. 1-29.
6. Parducci, A., Contextual effects: A range-frequency analysis, in Handbook of Perception Vol. II. Psychophysical Judgment and Measurement, E.C. Carterette and M.P. Friedman, Editors. 1974, Academic Press: New York. p. 127-141.

Sunday, 16 June 2013

Full of MSG

Like everyone, I suppose, I find myself receiving email updates from websites I once consulted and would otherwise have forgotten. One of these is which, as far as I can gather, started life dealing with questions of Asian identity. But for some time it has also been debating the question: just how dangerous is that common combination of sodium and glutamic acid – monosodium glutamate (MSG)? On the one hand, are those whose posts - correctly - point out that the (good) published studies fail to find adverse effects of MSG consumption over and above effects produced by a placebo. In response, the contrary viewpoints tend to have a much more personal tone, based on experiences that they attribute to this alleged toxin.  A recent post illustrates this:

“MSG is highly dangerous. For me, I didn't used to get reactions, but after decades of eating this stuff, now get raging migraines, heart fibrillation, insomnia, blurry vision, all from accidentally eating MSG in foods. …. As you age, you … start having to deal with some neuro damage from the stuff. I've seen family members, constant eaters of Chinese restaurant food, now have all sorts of neuro-degenerative issues …”

The origins of such beliefs make for an interesting study of how worries about modern foods combine with a fear of environmental toxins to create anxiety that requires a convenient place to be attached – in this case, MSG acts as the “hook”. 

From a scientific point of view, the question of MSG toxicity/allergy is largely settled in the negative. However, considerable interest remains in the question of why glutamate acts so reliably as a flavor enhancer. It is straightforward to demonstrate, for example, that savoury foods containing added MSG are evaluated as having greater flavor intensity as well as being more liked [1]. In this regard, MSG acts much like fat and sugar and this analogy has been used to in studies in which MSG has been used to promote liking for novel flavours.

Repeatedly pairing MSG with a novel flavor in solution results in that flavor becoming more liked [2], which is the same effect produced by either fat or sugar. The proposed mechanism for these latter preference boosters is based on the use of the energy provided by fats and sugars by the body, converting the otherwise ‘meaningless’ flavor into a (liked) signal that energy is being delivered. This is variously referred to as ‘post-ingestive’ or ‘flavour-nutrient’ conditioning. Either way, the idea is that a link is learned between the flavor and a positive consequence of ingesting something that is valued by the body. This argument is well supported by demonstrations that these conditioned learning effects only occur when the energy/flavor pairings happen in a state of relative hunger – that is, when the energy is most valued.

So, is glutamate an energy source, like sugar and fat? Possibly, although there is also evidence that the glutamate that we take in our diet is used for a variety of important metabolic processes [4] that could underlie the conditioned liking. Another persistent hypothesis is that the presence of glutamate is a signal to our bodies for the presence of protein. This makes intuitive sense, since glutamic acid is a key amino acid present in proteins. But while there has yet to be convincing evidence for one hypothesis over another, any or all of these effects could support flavor preferences.

Regular readers will recall the distinction made between liking and wanting (October, 2012: Learning to want). More recent research has shown that not only does the presence of MSG promote novel flavours into preferred ones, it acts also on motivation to eat, that is, wanting. Flavours conditioned with MSG increase appetite and promote increased consumption of the flavoured foods, at least in the short term [3]. A recent publication by Una Masic and Martin Yeomans from the University of Sussex has explored further the effects that added glutamate may have on how we eat [5]. They first raise the possibility that since glutamate makes food more palatable, we might expect increased intake of glutamate enhanced foods over the longer term. 

It is well known that palatable foods produce an initial appetizer effect – that is, appetite and intake increases following our first bite. Masic and Yeomans hypothesized that adding glutamate to foods also has an effect on short-term satiety and the longer-term satiation:
“MSG may lead to reduced satiation (as a consequence of its effects on palatability) but enhanced satiety, by acting as a cue for protein ingestion”.

In investigating this question, the researchers prepared three soups: a control that was low in energy, a more energy dense version and another that was higher in protein, each with or without added MSG. Initially, hunger decreased but only when there was no added MSG, and only in the context of added protein. To put this another way, adding MSG to a protein enhanced soup maintained hunger. Assessing hunger ratings for a longer period of two hours after the soup was consumed showed, as predicted, a significant suppression of hunger at least for the first hour after consumption. This time it was when MSG had been added, but again this was only evident in the protein enhanced version. 

These data suggest a very important role for glutamate in regulating food intake, at least for protein-based foods. In doing this, the data also enhance the link to protein signaling, proposed as an explanation for glutamate palatability. Satiety and satiation are known to be influenced both by the nutrients present in foods and by a food’s palatability. This study steps up the complexity a notch by showing how an ingredient that affects palatability can modulate both processes when it interacts with the nutrients in the food. We know already that taste (in the broad sense of the term) is the best predictor of what we eat. This study suggests too that a taste (in the narrow, more technical sense) can also be a strong influence of how much we eat and when we are likely to feel hunger again.

As a final thought, it is worth considering how those who brand MSG a toxin could possibly account for glutamate’s complex influence on appetite, hunger and palatability. Increasing food preferences and intake is usually considered incompatible with neuro-(or any other kind of)toxicity.

1. Fuke, S. and T. Shimizu, Sensory and preference aspects of umami. Trends Food Sci. Technol., 1993. 4: p. 246-251.
2. Prescott, J., Effects of added glutamate on liking for novel food flavors. Appetite, 2004. 42(2): p. 143-150.
3. Yeomans, M.R., et al., Acquired flavor acceptance and intake facilitated by monosodium glutamate in humans. Physiol. Behav., 2008. 93: p. 958-966.
4. Reeds, P.J., et al., Intestinal glutamate metabolism. J. Nutrit., 2000. 130: p. 978S-982S.
5. Masic, U. and M. Yeomans, Does monosodium glutamate interact with macronutrient composition to influence subsequent appetite? Physiol Behav, 2013. 116-117: p. 23-29.

Wednesday, 8 May 2013

Supertaste me!

Even if you are not one of them, it is a very appealing notion that some people have extra special sensory abilities. In discussing smell and taste, we tend to think that wine judges, expert food tasters, and perfumery ‘noses’ must have sensitivity far beyond our own in order to detect the incredible subtleties present in these products. This is certainly the case, at least to some extent. No one becomes a perfumer without a excellent sense of smell. But often the role of training, practice (as with any expertise), and motivation are not given enough credit in the creation of such super tasters and smellers.

By contrast, though, the existence of more general super-tasters has generated much interest recently to a great extent because they live among us, seemingly without effort on their part. Up to 25% of the population (although it does vary across cultures) can be shown to be highly sensitive to a range of food qualities, including basic tastes, texture and perhaps even overall flavour. 

That taste sensitivity had a genetic basis first received wide acceptance with the discovery in 1930 that a substantial proportion of the population were taste-blind to the bitter compound phenylthiocarbamide (PTC)[1]. Later research using a related compound, 6-n-propylthiouracil (PROP), identified not only bitter non-tasters and tasters, but also a subgroup of the tasters who were exquisitely responsive to its (for them) traumatic bitterness [2]. 

Two things made these discoveries of interest to taste and food scientists. The first of these was research showing that PROP tasters, and especially super-tasters, found other tastes – whether in solution or in foods or beverages - also much more intense. Their experiences with chilli were hotter, their cream was creamier, their coffee more bitter, their cheese sharper, and their textures grittier, thicker and more viscous. They were more sensitive to differences or changes within foods [3]. An imminent finding of x-ray vision couldn’t be ruled out. Inevitably these differences in perception translated to differences in food preferences. And this piqued the interest of nutritionists because if you avoid green leafy vegetables such as spinach because of its bitterness, you then potentially increase your risk of cancers. But it became complex, because you probably drank less alcohol, thus reducing your risks.

The second issue of interest, particularly to taste scientists, was the identification of the TAS2R38 receptor, the gene that expressed it, T2R38, and structural variations within the gene that corresponded to the phenotype of variations in sensitivity to PROP and PTC. This is exciting because for the first time, the effect of substituting one amino acid for another in a taste receptor could be shown to have consequences in terms of health, via perception to preferences and then food choices. 

The excitement over these potential links has generated a vast number of studies into PROP sensitivity and its perceptual and preference consequences. Many theses were completed. In part, the volume of research was due to the fact that PROP responses have been seductively easy to generate, typically using either an impregnated filter paper or a 10 ml solution, and a rating scale (although which rating scale has turned out to be crucial – see  [4]). However, the kryptonite in the ointment is in plain sight. TAS2R38 is a receptor for PROP/PTC, but not for other bitter compounds, sweetness, sourness, texture or the burn of the capsaicin in chillies.  To account for these relationships, something other mechanism is required. Fortunately, it was earlier shown that PROP intensity is highly correlated with the density of fungiform papillae on the tongue (FP; the bumps of the front surface of the tongue), and the taste buds that they contain. More FP means more intense tastes and, via the anatomical links that the trigeminal nerve has with taste buds, more intense burn and other mouthfeel sensations. At least, this is how it is assumed to work.

While this makes perfect sense – PROP intensity reflects other tastes/sensations via a common underlying cause, FP density – it does start to make the formerly simple measurement of PROP intensity relationships much more complex. Added to this complex mix, too, was the description of the genetics of other bitter taste receptors, including those that underlay the bitterness of coffee and grapefruit juice. And, of course, there is the as yet unknown genetics of variations in FP density.

At the recent 2013 Association for Chemoreception Sciences meeting in Huntington Beach, USA, John Hayes and colleagues [5] attempted to disentangle some of these relationships to provide a clearer picture of what PROP genetics does, and importantly does not, account for. By measuring the bitterness of quinine, the sweetness of sucrose, and the burn of capsaicin in addition to PROP bitterness and PROP genetics, Hayes was able to independently relate PROP phenotype and genotype to these taste and burn sensations.

As expected if a different underlying mechanism mediates the relationship between PROP and taste and oral sensations in general, the intensity of quinine, sucrose and capsaicin did vary with PROP intensity but did not vary with the genetic variations in receptor structure. In contrast, PROP bitterness directly reflected the genotype. Interestingly, though, how strong you rated capsaicin burn was a better predictor of quinine and sucrose intensity than was PROP bitterness. This is easy to understand when considering that the range of responses to PROP includes 20-25% who taste little or no bitterness – PROP non-tasters – as well as those who are medium- and super-tasters. In contrast, no one appears to be such a strict non-taster of quinine, sucrose, and capsaicin.

To return to the theme, where do we stand with the notion of super-tasting? PROP supertasters exist because they carry two alleles for tasting. But this is overlaid on the completely independent issue of whether or not an individual also has a high density of FP, and if they do, PROP will be even more intense. But this fact is of little interest as a way of predicting responses to foods, which never contain PROP. However, irrespective of your PROP taste genetics, you will still have more or fewer FP on your tongue. So, some people won’t taste PROP at all but will find quinine, or sucrose or capsaicin as very strong – in effect, you can be a PROP non-taster and a supertaster for all other oral sensations. 

As for predicting food preference and intake and their consequences, it looks like PROP at best will only ever be an imperfect index. That, in and of itself, is not cause for concern. While it does make the job more complex, there is clearly a way forward to finding an even better index of food perceptions and preferences.

A sensory system turns out to be complex. Who knew?


1. Fox, A.L., Six in ten "tasteblind" to bitter chemical. Science News Letter, 1931. 9: p. 249.
2. Bartoshuk, L.M., et al., PROP supertasters and the perception of sweetness and bitterness. Chem. Senses, 1992. 17: p. 594.
3. Prescott, J., et al., Responses of PROP taster groups to variations in sensory qualities within foods and beverages. Physiology & Behavior, 2004. 82(2-3): p. 459-469.
4. Bartoshuk, L.M., et al., Labelled scales (e.g. category, Likert, VAS) and invalid cross-group comparisons: what we have learned from genetic variation in taste. Food Quality and Preference, 2002. 14: p. 1125-138.
5. Hayes, J.E., et al., The primary qualities evoked by quinine, sucrose and capsaicin associate with propylthiouracil bitterness, but not TAS2R38 genotype, Paper presented at the Association for Chemoreception Sciences meeting, April, 2013: Huntington Beach, USA.

Monday, 25 March 2013

Flavour terroirism

It is difficult enough attempting to define the key influences underlying any flavour (see, for example, TasteMatters, July 2012: Driving a better tomato), but wine seems to be in a category all its own. Wine is chemically complex, but so are many foods and beverages we consume each day. What really sets wine apart (although some products such as cheese do come close) is its immersion in an artisanal mystique. The craft of winemaking resists scientific analysis, and this is particularly true of Old-World wines. After all, if winemaking was ‘just’ science, then any wine course graduate could plant vines in a paddock somewhere and 3 years later – hey presto! – Chateau Cheval Blanc ’47!

What really sets wine making apart is, of course, the land. In attempting to understand what makes a good cornflake, debates about the role of the soil in which the corn was grown are relatively uncommon. But the idea of terroir is now so entrenched in our appreciation of wine that its influence is taken for granted. The characteristic qualities of the land – the amount of clay or minerals in the soil or the local micro-climate – are seen as crucial to understanding not just the ripening and health of the grapes used in the wine, but the flavour of the wine itself. In essence, the wine flavor becomes an expression of the soil. This is sometimes taken to extremes, with the flinty character of a white wine being derived from the flinty soil, for example.

Beyond the romance of the idea of terroir, there are some practical reasons for linking the land to the flavour of the wines it produces. Thus, accepting this link means accepting too that wines from one region will in most cases taste quite different from those of another region, even if all other factors – grape variety, wine maker, storage type and so on – are kept constant. This is important, both for marketing purposes and for establishing that certain flavour characteristics are typical of a region and hence deserving of protected status. In turn, the idea of terroir underpins the rationale for using organic, or even the slightly whacky biodynamic, practices. It means too that the final say in what a wine tastes like cannot be left to consumer demands or market forces since the winemaker operates under constraints of the soil, and the soil determines what the wine ought to taste like.

Some of the attempts to study terroir have provided little support that this is an especially large contributor to flavour. In a descriptive sensory analysis of German Riesling wines from a number of wine estates, Fischer et al. [1] noted the huge variation in sensory properties among wines from the same vineyard, suggesting that terroir was a relatively minor influence on flavour, compared to the major influence caused by vintage and wine estate. They cite another study published in German by Wahl & Patzwald (1997) in which the researchers went to the effort of transplanting seven different soil types to the same vineyard to study the impact of soil type on wine composition and sensory quality of Silvaner wines. They reported no significant impact on wine ̄flavour of the soil type, beyond different grape yields.

In fact, a scientific analysis of the impact of terroir has proven difficult. Not only do soil types and climate vary with geography, but of course so do other factors including such things as the location of the vines relative to drainage and sunshine. Even when two locations have a winemaker in common, the entrenched belief by the winemaker in the influence of terroir may be an explicit or implicit source of handling the grapes or the wine in different ways.

Recently, Cadot et al. [2] surveyed wine producers from the Anjou region of the Loire in France to determine their concept of wine (flavour) typicality and how they thought that it related to terroir. Not surprisingly, for these producers, the main characteristic that explained both typicality of the wine and its flavour was the terroir. Soil and climate characteristics were important for 93% of the wine producers (compared to 65% for wine-making practices and 5% for harvest quality). The winemakers’ judgments of what constituted a typical wine of this region (and hence what was the main influence of terroir) were sensory attributes such as colour intensity, red fruits, and soft tannins.

In contrast, a descriptive sensory evaluation of the region’s wine produced a profile of the ‘perceptual typicality’ of the wines. Here, visual descriptors, spiciness and astringency, but not red fruits or soft tannins, were important. Moreover, when it came to those factors that distinguished the more prestigious style (Anjou-Villages Brissac) from a more quaffing variety (Anjou Rouge), only those technical factors under direct control of the winemaker - maturation time, vatting time, harvest date, and proportion of the Cabernet Franc grape – were influential.

Similar conclusions were drawn from a study undertaken some years ago by one of my students at the University of Otago, Sara Springhall [3]. Sara asked 27 experts/semi-expert wine tasters (all either teaching enology, undertaking enology courses, or members of wine clubs) to taste 13 Chardonnay wines sourced from three distinct regions in New Zealand - Hawkes Bay, Marlborough and Central Otago. According to, these regions are characterized respectively as having (a) high sunshine hours and variety of soil types; (b) Lots of sun, cool nights, low autumn rains and free draining alluvial soils; and (c) hot, dry summers, snowy winters, and soil structures that are very different to those of New Zealand's other regions, with heavy mineral deposits in silt loams.

The tasters were asked to sort and group the wines based on similarity of flavour and then provide descriptors for the most prominent sensory characteristics. The sorting data were analyzed by using the number of times that wines were grouped together as a measure of their “distance” from one another. This allowed the data to be represented as a multidimensional map, which showed both substantial overlap between regions (Central Otago and Marlborough) as well as clear separation (Central Otago and Hawkes Bay). The axes of the map (essentially, North-South vs. East-West) were shown to be related strongly to the common descriptors for the wines. The major axis, the one along which the wines differed most, was found to be associated positively with the woody and caramel attributes of the wines, and negatively with the wines’ sourness. Variations in wine citrus flavours were associated with the secondary axis.

These axes were also strongly associated with the chemical characteristics of the wines. In particular, alcohol and sugar content varied positively with the main axis of the map, while pH correlated negatively and volatile acidity positively with the minor axis.

What all these data mean is that both sensory attributes and chemical characteristics underpinned the ways in which the wines were sorted. However, since the wines grouped according to geographical regions were not strongly aligned to either the sensory or chemical dimensions on which these wine experts sorted the wines, the data suggest that the most important influences on the flavor of these wines occurred during winemaking. Woody and caramel qualities, for example, generally originate as a result of contact with oak during fermentation and maturation, while variations in citrus flavours, alcohol and sugar content are linked closely to when the grapes are harvested.

A failure to reveal the impact of terroir does not mean that there aren’t better or worse soils or microclimates in which to grow grapes that make good wines. But it does mean that we ought – for the moment – to be sceptical about wine producers’ claims that wine flavours are to any great extent a product of the soil. Alternatively, you can accept the claims, because of the romance of the idea …. but to be consistent, it’s probably a good idea to start asking your bartender about the soil in which the hops were grown next time you order a beer.

1.         Fischer, U., D. Roth, and M. Christmann, The impact of geographic origin, vintage and wine estate on sensory properties of Vitis vinifera cv. Riesling wines. Food Qual Pref, 1999. 10: p. 281-288.
2.         Cadot, Y., et al., Characterisation of typicality for wines related to terroir by conceptual and by perceptual representations. An application to red wines from the Loire Valley. Food Qual Pref, 2012. 24: p. 48-58.
3.         Springhall, S., et al. Multidimensional sorting applied to understanding flavour variations in Chardonnay wines in 5th Australasian Association of Chemosensory Science Annual Scientific Meeting. 2002. Heron Island.