Green’s Dictionary of Slang

(later Irish) anything mouldy or sour, esp. a taste (in food or drink) that is other than one expects.

1864, 1867, 1870		Hotten Sl. Dict. 252: tack a taste foreign to what was intended; a barrel may get a tack upon it, either permanently mouldy, sour, or otherwise.
1873		Sl. Dict.
1939		‘Flann O’Brien’ At Swim-Two-Birds 223: I’ve had an odd pint of that tack in my time.
1953		B. Behan ‘The Confirmation Suit’ After the Wake (1981) 40: They tasted it [...] Some said it was paste [...] and there were other people who maintained it was glue. They all agreed on one thing, that it was dangerous tack to leave lying around.
1962		B. Behan Brendan Behan’s Island (1984) 150: It was dangerous tack to leave lying around, where there might be young children.
1997		Share Slanguage.