Chitosan (positive charge): As the name implies, it is composed of chitin, which is the structural element of the exoskeletons of crustaceans, such as crabs, shrimp and other shell fish. Chitosan is especially popular in clearing white wines, since it does not require the aid of tannins to clear, as do some fining agents like gelatine. When used with negatively-charged Kieselsol it is an effective remover of most suspended proteins and solids.
Chitosan and Kieselsol are often sold as a set, in sealed liquid envelopes as fining A (negatively charged Kieselsol) which is added to the wine first, and then fining B (positively charged chitosan) added about a day afterwards. Chitosan has a reputation for being fairly gentle on the character of finished wine.
Kieselsol (negative charge): Also known as silicon dioxide. Kieselsol works well with gelatine as a clearing agent, since it acts as a tannin substitute and works well to remove bitterness from white wines. When used with gelatine, the gelatine is added to the wine first, and then 24 to 48 hours later, a very small amount of Kieselsol is added, and should be racked off within 2 weeks. Kieselsol also works with chitosan (see the section on chitosan earlier).
Gelatine (positive charge): Gelatine is an animal protein. Like Bentonite, gelatine can be applied as a clearing agent pre- and post-fermentation. Gelatine is recommended for red wines since its positive charge helps reduce excessive tannins (tannin carries a negative charge). It can also be used on white wine to remove the bitter taste of excessive tannins. But in white wine excess gelatine can create a protein instability and develop a haze of its own. To prevent over stripping of white wine, gelatine can be used with Kieselsol. Kieselsols negative charge works as a tannin substitute to neutralize excess gelatine in the wine. The two agents with different charges working together also have the potential to both reduce astringency, and collect a greater number of charged solids.
Gelatine is available in powder, but some manufacturers offer it in liquid form. However, being an animal protein, it has a limited shelf life and the size of the liquid batch you purchase should be considered if you cant use it all in one application.
If gelatine is used to reduce astringency in wine, it is easier to regulate the required dosage if you use the powdered form of this fining agent.