Chitosan
An antimicrobial fining that targets Brettanomyces and clears haze.
Typical dose
Fungal chitosan around 0.1 to 0.5 g/L; follow the product sheet.
When to add it
On a finished wine, to lower a spoilage population or polish clarity.
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
Depends on the source. One form is animal-derived and an allergen, another is not, so the product, not the name, decides.
In practice
Reduces Brettanomyces and other spoilage organisms while also clarifying. The fungal form, from Aspergillus, is acceptable to vegans; the shellfish-derived form is an allergen, so the source matters. It will not undo aromas Brett has already made; it lowers the population that would make more.
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 antimicrobial and reduction treatment