Winemakers add bentonite to prevent protein haze in white wines. Although this treatment reaches its goal, it also leads to volume losses and sometimes a decrease in wine quality. The question is: are there alternatives available?

Protein haze – some background information

The removal of proteins is a key step during the production of white and rosé wines to avoid the possible appearance of a harmless, but unsightly haze. Haze formation is an aesthetic problem that consumers usually regard as a fault (e g microbial spoilage) leading to potential economic losses. Proteins that are responsible for haze formation in wine have been identified as pathogenesis-related proteins of grape origin. The most abundant class of haze-forming proteins are chitinases and thaumatin-like proteins and are continuously produced in the grape berry and even more so in response to pathogen attack. Because of their physical structure and properties, these proteins are very resilient and are not or poorly degraded during the course of fermentation. Over time and upon exposure to warm/hot temperatures during storage for instance, these proteins denature and aggregate into light dispersing particles resulting in what is referred to as ‘haze’.

The mechanisms of haze formation has received much attention from researchers over the last decade. It is complex by nature and depends on several factors, one of the most important being the presence of sulphate. The removal of these proteins is usually achieved via bentonite fining, but several issues including volume loss, aroma stripping and sustainability have been identified with the use of this clay. Several strategies have therefore been investigated over the past few years. One of the most attractive alternatives would consist in degrading these haze-forming proteins with enzymes. This is particularly appealing since enzymatic degradation of proteins (protease activity) would not lead to any of the issues mentioned for bentonite and could have the additional benefit of releasing yeast assimilable nitrogen.

Where does one find enzymes capable of degrading haze-forming proteins? …

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