Casein
potassium caseinate, milk protein
Treats browning and light oxidation or taint in whites.
Typical dose
Bench-trial, roughly 0.1 to 0.5 g/L.
When to add it
On a white showing early browning or a mild off-note.
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
No. Animal-derived, and usually an allergen to declare, so it rules out a vegan label and needs care on the ingredients list.
In practice
A milk protein that lifts brown colour, oxidised character and some light taints out of a white, working partly by adsorption as it precipitates. It must be dispersed fresh because it clumps, and it is a dairy allergen, so it is declared.
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.
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.