This week, I overheard some fellow professionals at a wine tasting describing a 1998 Pinot Gris from Alsace as smelling of petrol. His neighbour quickly agreed with him. I was tasting the same wine at the same time but found nothing that even vaguely resembled petrol flavours. Which of us was wrong?

Assessing wine is so subjective that it's usually impossible to tell someone that they are mistaken, especially when talking about flavour. So long as it's within the bounds of reason, it would be futile to scrap with someone over the precise fruit aromas in a Sauvignon Blanc or the spice character in an oaky Bordeaux.

Petrol is quite a distinct flavour, however, and is often connected to a particular compound called norisoprenoid hydrocarbon 1,1,6-trimethyl-1,2-dihydronaphthalene*, which I'm sure was on the tip of your tongue. It was evidently on the tongues of my fellow tasters anyway, arf arf. Better known as TDN, this is the compound known to be present in many aged Rieslings, giving them a distinctive petrol flavour.

I feel reasonably comfortable identifying TDN - it's a scent that stands out, and isn't easily mistaken for other flavours, unlike fruits or spices, for instance. I felt quite sure that there was no petrol flavour in this 1998 Pinot Gris. So I turned around and barked at them that they were utterly mistaken, and that as a Master of Wine my opinion on the matter was final.

Obviously, I didn't do that. In fact, this example is of little consequence, but it got me thinking. Because wine tasting is subjective, there are very few instances where you can be truly wrong. Unfortunately, this allows all sorts of dubious opinions, excuses and statements to go unchallenged, making an already arcane activity even more obfuscated. (I've written about this before, in my Off Licence News column.)

This is on my mind at the moment because I'm just starting to mentor three new MW students. Helping them get better at identifying wines in the examination is a big part of the process, and blind tasting exams are one of those rare instances where you can be definitively, chronically wrong.

Figuring out why and how you misinterpreted a wine is a really important discipline, and is one of the most valuable experiences of becoming an MW. It can also be quite painful and hugely embarrassing. That's one of the main reasons that people never attempt to correct each other when tasting outside an academic scenario. Occasionally this leads to bizarre conversations where two tasters discuss a wine in agreement with other while using totally contradictory statements.

Speaking up in such instances would appear incredibly rude, but not doing so allows all sorts of nonsense to proliferate. Some people might say there's nothing wrong with that. But they're so wrong.

*according to the 4th edition of The Oxford Companion To Wine.