Identification and quantification of resolubilised polyphenols from fining precipitation

The aim of this study was to better understand the colloidal phenomenon involved in the fining process and to determine how many polyphenols are impacted in this process. Different types and compositions of fining agent were used to fine the wine. Some of them were pure and based on animal proteins and plant proteins, while others comprised a mixture of different matter, like PVPP and plant proteins, or PVPP, plant proteins and bentonite. Before and after fining, five different analyses were performed on the wine to characterise the polyphenolic composition and content. In order to determine polyphenol loss more precisely during fining, a new method was developed to quantify and characterise polyphenol precipitate using fining agents. This new method allowed us to find some drastic differences between the fining agents in term of total polyphenol precipitation, as well as in the composition of the precipitated compounds. Indeed, a group of anthocyanins present in low levels in wine (i.e., p-coumaroylated anthocyanins) became the most represented in the fining precipitate. Similarly, differences were also observed between the fining agents in the composition of precipitated condensed tannins. Fining agents without PVPP did not precipitate monomeric or dimeric flavan-3-ol or crown tannins. Some differences were also observed between the fining agent composed of plant-derived protein and that comprising gelatin.