Plasters, Islay whisky, TCP, smoke, clove; very few beers should taste like this.
A phenolic aroma and flavour should be present in some beers, including wheat beers and some Belgian ales, where it gives a faintly smoky or clove-like aroma, but if you find it in a pale ale, lager or bitter then things aren’t quite right. And this is another off-flavour which some people are more susceptible to tasting than others.
The phenolic flavour most often comes from a reaction between chlorine and the phenolic acid naturally found in malt; this could be from the chlorine content in the water (especially if it’s untreated) or from a cleaning solution used in the brewery which contains chlorine.
This aroma and flavour can also come from the yeast (wheat beer yeast, for example, will produce it, and I’ve had a few wild beers which have smelt like smoky swimming pools). Peated malt will also have this flavour but it will often add a different character more along the lines of charred toast than TCP.
If a phenolic flavour is appropriate to the style then it’s fine. I’m sensitive to the flavour in beer and I don’t like it at all – I like wheat beers but not ones which are heavy on the clove. I also sometimes taste it as flinty or like concrete. Interestingly, however, I love massive smoky whiskies (and I really like stouts aged in smoky whisky barrels - if the flavour is from a barrel like this then it isn't an off-flavour). When it shouldn’t be there it dives out the glass at me and I find it undrinkable.
Is this a flavour which you can easily detect in beer? If so, do you like it or hate it?
I only realised recently that it was the clove-like flavour which I didn’t enjoy in wheat beers and some Belgian ales. I typically described it as ‘spicy’, which does no justice to what it is; it was just the word which meant to me that it tasted a bit funny.