I had a very nice tasting grape wine which I used isinglass Finings on which has not cleared the wine and left it with a horrible taste. Does anybody know why this would occur?
It may have got contaminated at some point after your sample that tasted good. Either from drawing samples or addition of the fining.
Finings can change flavor. By reducing particles that contribute to the flavor, like tannins.
Isinglass is typically a second or final clarifier as it doesn't do well for heavy haze.
This is actually a good article much aplies to fining beer too. https://winemakermag.com/26-a-clearer-understanding-of-fining-agents