Did the Sauvignon Blanc in your glass, which was so refreshing in the past, make you pucker like a Victoria’s Secret model? Did the over-oaked Cabernet that reminded you of licking a fence post taste just fine after a sip or two? Why did the wine that was so good at the winery taste so ordinary once you brought it home?
Flavors in wine can seem like flickering hallucinations—now you taste it, now you don’t. But sometimes it is not the wine that is changing. It’s our palates that are fooling us because of two related phenomena: adaptation and perceptual contrast.
Adaptation happens when sensitivity to a stimulus is decreased with additional tasting. The more you taste of something the less intense the flavor will seem. That’s why a wine that is out of balance at first might be fine after a few sips (or alternatively why a wine that is initially exciting might seem dull after awhile.) Adaptation sets in immediately. Even the tastiest dish will seem boring and flavorless after a few bites unless you have something on your plate to disrupt the adaptation. The same is true of wine.
Perceptual contrast occurs when a perceptual stimulus is influenced by a contrast with other stimuli. So if you have been tasting subtle, restrained wines, a high-alcohol fruit bomb will seem impressively intense and flavorful, although when tasted alone it may be ordinary. But if you’ve been tasting big, full-bodied wines, a subtle, lighter wine will seem disappointingly meager.
This is why the host of a wine tasting will insist on serving dry or light-bodied wines first before full bodied or sweet wines. But this convention by itself will not eliminate all adaptation or perceptual contrast effects. All components of a wine—balance, structure, acidity, alcohol, and flavor profile are subject to the distortions of adaptation and perceptual contrast, and no single sequence will give equal weight to each characteristic.
A recent experiment at UC Davis shows how this effect works with alcohol. 34 trained subjects tasted several series of Cabernets, some arranged from low to high alcohol, others from high to low alcohol, and others presented randomly.
Those who started with lower alcohols could detect the relative viscosity, more intense aromas and an “extraordinary perception of sweetness” in the higher-alcohol wines. Those who started with higher alcohols had a tougher time assessing alcohol levels, found lower-alcohol wines less smooth and tasted more herbaceous flavors, a trait often criticized in modern Cabernet.
For ordinary consumers, failure to minimize these misperceptions means a disappointing purchase; for professional wine tasters it can mean inconsistent, incoherent judgments. And although being aware of these effects can help moderate them, they are too powerful to be eliminated through awareness alone.
The only antidote is crackers (or other flavorless snacks) and water consumed whenever a wine with different characteristics from predecessors is tasted. (Time also matters if you wait long enough for your palate to cleanse itself.) Most wine tasting venues supply crackers and water, but they are too often ignored. Even among professionals at wine competitions where a judge may blind taste 100 wines, there is insufficient attention paid to palate cleansing, which threatens the objectivity of the results, especially when wines are haphazardly thrown together without much thought given to sequence.
Our senses evolved as a way of protecting the body from harm. They adapt to the ordinary in our environment in order to pay more attention to new, painful, or poisonous stimuli.
Those pesky survival strategies can make life difficult.
Exploring the Philosophy of Food and Wine 
I completely agree about the importance of contrast for wine tasting, and that it is scandalous that this point is all but ignored in the tasting world. I’m a little more skeptical than you are here about claiming that it’s desirable to surpress such effects. But even if you wanted to do that, there’s a further question about why we should use crackers/water, which surely do have flavors of their own, and whose employment would seem to replace one kind of adaptation by another. Charles Spence was arguing at one point that if you are really trying to return to a psychophysically neutral starting point, you should make tasters adapt to artificial saliva. (Artificial so it can be made consistent between tasters.) Sounds pretty unpleasant if you ask me….
Jonathan,
Assuming we’re talking about water crackers or perhaps saltines, whatever adaptation there is to the crackers would be largely irrelevant when assessing features of the wine such as body, alcohol level, acidity, and flavor profile. That is, it is not adaptation simpliciter but adaptation to particular features of wine that is problematic. If I’m not mistaken, water returns the mouth to its natural PH level, which would be helpful in assessing acidity.
I too will pass on the artificial saliva. That seems pointless. We review wines for human beings who presumably have “natural” saliva, albeit with individuating characteristics. I doubt that the “view from nowhere” is the gold standard for wine reviews.
Agreed, one of the dimensions for which it would be nice to have adaptation return you to a consistent baseline is pH (more accurately: perceived acidity); and agreed that water can get pretty close on that dimension. But I think it’s too quick to assume that water/crackers will get you to a neutral point on all dimensions that affect our tasting experience (or that the your list of ostensibly relevant dimensions is exhaustive as far as our tasting experience). Part of what’s cool and interesting about the adaptation question for tasting — and about tasting itself — is that no one has a very good understanding of just what dimensions are relevant to the experience. Nor their mutual interactions, their temporal profiles, their differential susceptibility to contrast effects by different stimuli, etc.
Here’s a related issue. One of the reasons many cite for encouraging adaptation is to provide a level playing field for all the wines tasted. As far as that particular motivation goes, however, you don’t need the adaptation to be neutral in any way. It would make for a perfectly level field if every wine were tasted after adaptation to lemon juice, even if this would presumably mask some components and enhance other components of our tasting experiences. Of course, psychophysicists standardly aim for something considered much more neutral as their adaptation mask (e.g., visual adaptation to darkness, auditory adaptation to silence). But this just invites the question: in what good sense are those targets neutral? And is that important for the psychophysics per se?