What is the purpose of using bentonite clay in winemaking?

The purpose of using bentonite clay in winemaking is primarily for protein stabilization and clarification. Bentonite is a type of clay with a high surface area and a negative charge. Wine contains proteins that can cause haze or cloudiness to develop over time, particularly when exposed to heat. These proteins are typically unstable and can aggregate, leading to visible particles in the wine. Bentonite acts as a fining agent by attracting and binding to these positively charged proteins through electrostatic interactions. The bentonite clay, with the bound proteins, then settles out of the wine, either naturally or with the aid of filtration, resulting in a clarified and protein-stable wine. This prevents the formation of haze in the bottled wine, ensuring its clarity and visual appeal. In addition to protein removal, bentonite can also remove other undesirable compounds, such as certain phenols, which can contribute to bitterness or browning. The amount of bentonite used varies depending on the wine's protein content and stability, as excessive use can strip desirable flavors and aromas. Winemakers conduct bentonite fining trials to determine the optimal dosage for each wine.