PVPP
polyvinylpolypyrrolidone, Polyclar
A synthetic that removes browning, pinking and bitter phenols.
Typical dose
Bench-trial, roughly 0.1 to 0.75 g/L.
When to add it
On a white or rose that is browning, pinking or bitter.
Legal limit
No specific limit that this reference states. Additions are still governed by the treating-materials rules where you make wine, so check them.
Vegan
Yes. Nothing animal-derived, so a wine fined with it can still be labelled vegan.
In practice
Targets the small phenolics behind browning, pinking and a hard bitter finish, more selectively than carbon and without stripping as much else. It is an insoluble plastic powder that is filtered out entirely and leaves nothing behind, and it is vegan.
Linked faults are the ones this addition either treats or, used wrongly, causes. The fault page says which, and whether it can be undone.
Others in fining and clarification
Bentonite
Adsorbs unstable protein to prevent haze in whites and roses.
Isinglass
Fish-derived collagen that polishes whites to brilliance at a tiny dose.
Gelatin
Collagen that strips harsh tannin and astringency from reds.
Egg white
The traditional, gentle softener of barrel-aged red tannin.
Casein
Treats browning and light oxidation or taint in whites.
Kieselsol
A negatively charged fining, paired with gelatin for a compact lees.
Sparkolloid
A polysaccharide clarifier for stubborn hazes that resist other finings.
Activated carbon
A blunt last resort that strips colour and off-odours together.
Plant protein fining
A vegan substitute for gelatin and isinglass.
Diatomaceous earth
A filter aid, rather than a fining, for wines too cloudy to filter.