Bentonite fining in cold wines: prediction tests, reduced efficiency and possibilities to avoid additional fining treatments

Abstract

Bentonite fining is widely used to prevent protein haze in white wines. Most wineries use laboratory-scale fining trials to define the appropriate amount of bentonite to be used in the cellar. Those pre-tests need to mimic as much as possible the industrial scale fining procedure to determine the exact amount of bentonite necessary for protein stability. Nevertheless it is frequent that, after fining with the recommended amount of bentonite, wines appear still unstable and need an additional fining treatment. It remains a major challenge to understand why the same wine, fined with the same dosage of the same bentonite, achieves stability in the lab, but not in the cellar. Presently unclear is the role, wine temperature plays in this issue. The impact of wine temperature, pH and mixing, on the fining efficiency of different bentonites has been studied in a Gewürztraminer wine. Three different types of bentonites were used in this trial; a sodium-bentonite, a sodium-calcium-bentonite and a sodium-calcium-bentonite which additionally contains tannins. This paper shows the effects of low wine temperatures on the efficiency of three different commercial bentonites. Further, the effect of an additional whirling up of the settled bentonite is studied to understand if this could be a measure to increase the effectiveness of the fining treatment. Wine temperature has an impact on the performance of the bentonite fining. Low temperatures make it more difficult to achieve protein stability for all the different bentonites in investigation. Not one single wine achieved protein stability when it was fined at 4°C with any of the three bentonites in investigation. At low wine temperature always an additional fining treatment or anew shaking of the wines was necessary to achieve protein stability. Especially the sodium-bentonite Bentogran showed an important loss in efficiency when wines were cold. NaCalit and Super Black Jell were less affected from low wine temperatures and achieved tolerable turbidity levels when bentonite was stirred up again after one week of contact. Mixing up the settled bentonite once again when settled is an efficient way to improve the effectiveness of the bentonite fining. This simple and easy to carry out measure can be an interesting strategy for the praxis to avoid additional fining treatments. Further, to reduce the discrepancy among the laboratory and cellar conditions, two possibilities exist: (a) fining trials could be conducted at the same temperature as the wine in the cellar has, (b) bentonite fining in the cellar should not occur at too low wine temperatures. These are relevant findings for winemakers who do their bentonite fining in cold wines and deal with varieties with a high wine pH.