Developing Botrytis cinerea as a non-GM enzyme producer for the removal of haze-forming proteins under normal winemaking conditions

Improvement of winemaking processes has long been a focus of research efforts to increase the efficiency and economy of the billion-dollar wine industry. A key process for improvement is alternative methods of heat stabilizing wine. Wine haze is caused by the aggregation of grape proteins following heating, usually during transport and storage, making the wine unappealing to consumers. Fining with bentonite clay is the most common method of heat stabilizing wine. However, bentonite fining can remove desirable compounds from wine and creates environmental waste. Additionally, 3 to 10 % of the total wine volume is sequestered in the bentonite lees, requiring rotary drum filtration to remove residual wine which greatly reduces the quality and value of the wine.

Microbial enzymes have been the recent focus of advancement in this area, with many showing promise as a feasible alternative to bentonite. Unfortunately, these enzymes generally require heat treatment to activate the enzyme and denature the haze-forming proteins, a process that is out of reach for many wineries. Recently, proteases from the fungus Botrytis cinerea have been studied for their effect on wine haze-forming proteins, under normal winemaking conditions, and a reduction in haze-forming proteins was observed. However, the protease was created using recombinant expression which is not accepted in winemaking.

This research focused on developing a protease preparation from B. cinerea without genetic modification. Wild B. cinerea isolates were screened for protease production in optimised liquid medium, then protease production was scaled up to 1 and 10 L bioreactor volumes. The large volumes of protease containing supernatant was then concentrated and the protease preparation tested in three white wines under normal winemaking conditions, showing a reduction of 0.5 g/L bentonite required for heat stability of a Sauvignon Blanc wine and no significant difference in a Chardonnay and Pinot Gris.