Many years ago I used to sometimes go out for a drink with my father and my Uncle Bill, who is long since deceased. We would get three pints with dense, creamy heads, but he only had to take a couple of sips from his glass to make the head completely disappear, leaving him with the proverbial beer that was as flat as a fluke, whereas the other two heads remained intact. It must have been some characteristic in his saliva – maybe unusually acid – which reacted adversely with the beer.
Over the years I have come across a number of other individuals who have the same effect on their beer, including one with the perhaps appropriate name of Malcolm Swallow.
I have to say this makes a pint of beer look extremely unappetising, but it doesn’t seem to deter those who suffer from it. I wonder whether this is a phenomenon others have ever encountered.