Which heat test can realistically estimate white wine haze risk?

Abstract

Different heat tests are used to predict the dose of bentonite necessary to prevent wine haze after bottling. The most used tests are 60-120 min. at 80°C. Nevertheless, there is a lack of information about the relationship between these tests and the turbidities observed in the bottles after the storage/transport of the wines in realistic conditions, when temperatures reach 35-42°C during 3-12 days.

In this study, 6 heat tests were applied on 14 Sauvignon wines (France) : 5-30-60 min. at 80°C and  30-60-120 min. at 50°C. The results were compared with the turbidity reached by the wines under real Summer conditions, i.e temperatures corresponding to heat waves (35 to 46°C, from 1 to 14 days) and representing 6 tests too. The 66 Pearson correlation coefficients (PCC) were calculated for all of these 12 heat tests when compared two by two.

The turbidities of the wines subjected to Summer temperature conditions (1 day at 35°C, 4 days at 35°C, 4 days at 35°C + 1 day at 43°C) were highly correlated with the turbidities developed by the Sauvignon wines after heating 30 or 60 min.  at 50°C. The PCC were between 0.980 and 0.989. The higher PCC were observed between Summer realistic conditions and a heat test during 120 min. at 50°C with PCC values between 0.993 and 0.997. The PCC between Summer heatings and a heat test during 60 min. at 80°C were interesting (0.911-0.924) but not so high.

Beyond these relationships, it is essential for a winemaker to consider the turbidity reached by the wine after a heat test. The problem is that turbidities observed for a wine after different heat tests can reach 2, 8 and 34 NTU when the wine was heated a 4 days at 35°C+ 1 day at 43°C, 2hrs at 50°C and 1hr at 80°C respectively. In these conditions, it is very problematic to decide what is the correct dose of bentonite to ensure a complete colloidal stability with time of the wine.

Proteins implicated in the white wine haze are essentially thaumatin-like proteins (TLPs) and chitinases whose temperatures of denaturation are around 55°C and 62°C respectively. It explains why the heat tests at 80°C, even if correlated with realistic tests give excessively high values when compared with what can happen to a wine during a hot Summer. This leads the winemaker to use excessive bentonite doses given stripped wines whilst lower doses could be sufficient to ensure the absence of haze in the bottle.