Though I’m no medical doctor (and certainly don’t play one on TV), from what research I was able to pull together, if I personally had a shellfish allergy I would feel comfortable using chitosan products to clarify my wine. I will let you make up your own mind (in conference with your physician, of course), but from what I understand, seafood allergies derive from proteins in crustaceans and shellfish, not from materials in their shells. Chitosan is a manufactured product that (in some cases) is derived from chitin in the shells, a natural polymer. During the manufacturing process, the shells only (no fleshy protein bits) are used, and any protein that could possibly be clinging is removed. Most winemaking supply houses (AEB, to name one) these days are producing chitosan from Aspergillus niger, a fungus, so there is no seafood involved.
Chitosan is a great flocculating agent in wines. It precipitates solids and is a very efficient clearing agent — basically you add it to your wine, it gloms on to solids, and then falls out of solution to the bottom of your container. If you rack cleanly enough (giving the solids plenty of time to settle) you should be able to leave the chitosan fining agent behind in your container, along with the tannins and wine proteins it pulled out. It also is an important antiseptic agent and can inhibit microbiological activity, helping to prevent volatile acidity (VA) formation as well as in stopping unwanted fermentations. Because of this, it’s not wise to use it right before you might want a wine to go through malolactic fermentation. It can be very useful in preventing Brettanomyces for wine stored in wood.
I think chitosan is an under-utilized winemaking ingredient that more home winemakers should become accustomed to using.
