Protein haze in bottled white wines: How well do stability tests and bentonite fining trials predict haze formation during storage and transport?

Abstract

Based on work undertaken over 30 years ago, most Australian winemakers use a heat test (80oC for six hours) to check white wines for protein stability. Some winemakers consider that this test is too severe, resulting in wines being over-fined with bentonite. This paper presents the results of a study comparing the predictive ability of this test, assessed either by eye, by nephelometry or by optical density, with that of two alternative assays (80oC for 2 hours and the Bentotest), through the use of storage trials of 8 wines designed to mimic commercial conditions of transport and storage of wine. One of the 8 unfined wines failed to develop haze even under the more severe storage conditions of this study (35oC for a month or fluctuating between 20oC and 35oC for 8 days) and only 6 of the 8 unfined wines developed haze under ‘best practice’ storage conditions (13oC–17oC for 16 months). All the wines fined with bentonite at dosage rates determined by the three predictive tests used in the main part of this work remained bright in bottle after storage trials at 13oC–17oC for 16 months, 35oC for 1 month or fluctuating between 20oC and 35oC for 8 days. Therefore the least severe stability test, heating at 80oC for 2 hours, which generally indicated lower dosage rates in this study, accurately predicted short to medium term stability for these wines under these storage conditions.