The major source of proteins in wine is the grape. Of the above, bentonite fining is a common practice in wineries today. The mechanism of fining includes coagulation and mechanical entrapment. Coagulation works because colloidal particles bind with oppositely charged fining agents. They cluster together and increase in density, and eventually precipitate out of solution.
Mechanical entrapment is a co-mechanism of coagulation.
While a cluster settles, the complex becomes a net that traps other impurities along the way. However, the protein fragments responsible for haze formation are not those primarily removed by either bentonite fining or ultrafiltration. A model made of gelatin and tannic acid suggests that the fixed numbers of binding sites on proteins will bind to a fixed number of polyphenols by hydrogen and hydrophobic bonding. The amount of protein alone does not predict haze formation. Data indicate that the total protein analysis does not correspond to protein instability.