One of the pitfalls in tasting is the way that our sensory systems are quite malleable. Take vision, for example. If you are out in the sunlight and then walk into a slightly darkened room, it takes a while before you can see anything. Your visual system adapts to the ambient conditions. We take this for granted.
Now if you have been wearing coloured sunglasses, your visual system will have adapted to their tint, and when you take them off, everything will have a strange colour cast that takes a few minutes to lose. This is one piece of evident that argues for the subjectivity of colour perception.
A similar sort of adaptation takes place with the sense of smell. It’s called desensitization.
We can enter a room or a home and find it incredibly smelly, but then after a while we get used to that smell. This is an important ability: the strong smell would otherwise override more subtle smells. It’s not a complete adaptation, because some smells are powerful enough that they are merely dampened down. But it can explain why some people can have terrible body odour problems but not seem to notice it themselves – if they did, you’d assume they might do something about it.
Aside from desensitization, there is also a phenomenon called cross adaptation. This is when the process of adaptation to smell X causes some adaptation to smell Y. Now desensitization is problematic for wine tasting, but cross adaptation may be even more dangerous.
If there is a recurring smell during the tasting process, then you will become desensitized to that smell. It might be a wine component, or it might be an environmental smell, such as coffee or paint fumes or cooking smells. If the smell is a wine aroma, this will change your perception of the wine without being aware of it. A lengthy flight of the same kind of wine could be risky in this regard.
Cross-adaptation is even more of an issue because a smell unrelated to the wines you are tasting might change the perception of a particular wine component and thus the perception of the wine. The big problem with this is the sheer unpredictability of the process.
Surprisingly often I have sat with people and drunk a bottle over an evening, and then found ourselves commenting on how much the wine changed in the glass or decanter. The assumption here is that it is the wine that has changed; this may not be the case – it could be us.
Can anything be done? If we are judging wines it is sensible to work in short flights. The tasting order among judges needs to be mixed up (ideally randomised, but having one judge work backwards could help and is simpler to administer). Switching from a flight of wines of one type to a different type makes sense, and keeping this alternation going through the day would be wise. Any noticeable aromas in the room should be eliminated. And judges should have regular breaks.