Bentonite
sodium or calcium montmorillonite clay
Adsorbs unstable protein to prevent haze in whites and roses.
Typical dose
Bench-trial, usually 0.25 to 1 g/L for whites and more for very unstable juice. Confirm with a heat test.
When to add it
On juice or finished white; heat-test every white before bottling.
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
The only fining agent that reliably prevents protein haze after bottling, which is why a home white that clouds in a warm room almost always skipped it. It is a swelling clay carrying a negative charge that pulls out positively charged proteins. The right dose comes from a bench trial and a heat test, because too much strips aroma and body with the protein.
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
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.
PVPP
A synthetic that removes browning, pinking and bitter phenols.
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.