Of course we all have stories of thinking a wine is higher (>15%), looking at the label, and being vindicated by seeing 16.2% on the label. And of course we rarely admit or remember the times when we have the same feeling about a wine and look at the label and see 13.8%. Additionally, labels from CA typically lie and often that 14.5% Alc. may be 15.8%, and you are none the wiser. I wish I had catalogued the many tastings where I heard someone say, that is definitely hot and has high alcohol when indeed the wine was within the normal range. But alas I have not, so I turned to the literature to find evidence for our ability to distinguish alcohol as alcohol in wines.
Ill present my conclusion: there is very little if any evidence that we can distinguish alcohol as alcohol even between wines with up to 4% difference in alcohol by volume. But of course it is not as if alcohol is not critical to or has zero impact on OTHER attributes such as bitterness or sweet perception. I have been developing this thought internally for some time but reading an article for my post on sulfur and flavor also provided an impetus to look into ethanol perception. That study by Filipelo et. al. demonstrated that it took raising the alcohol to 16% from 12% in a red wine before a significant difference could be detected between wines. That does not make 16% some magic number, rather it suggests that you need more alcohol than most people would think (if we are honest with each other) it takes to create a difference. I have seen this corroborated by a rudimentary difference test done in my sensory class at UC Davis. Incidentally, the same study also provided evidence that alcohol makes the same amount of sugar in two solutions seems sweeter in the solution with alcohol (they did it in water versus in alcohol).