Filtering out Brett

By Karien O'Kennedy
The aim of the study was to compare the efficacy of filters with different compositions and pore sizes to remove Brettanomyces from wine. 

Project layout: 
A red wine, treated with hydrogen peroxide to remove SO2, was inoculated with Brettanomyces at a rate of 1.6 x 106/ml.
Seven different filters/pore sizes were compared for efficacy using 47 mm diam discs of each filter medium. The filters evaluated were polypropylene (PP, 0.6 and 1 µm), borosilicate glass microfiber (GF, X and V) and polyethersulfone membrane filters (PES, 0.45, 0.65 and 1.0 µm).
Filtered wine was collected and plated for microbial cell counts on plates containing bacterial and fungal inhibitors.

Results:
-The PP filters had very low retention for Brett cells. The 0.6 µm filter was marginally better than the 1.0 µm one.
-In the case of the GF filters only the GF X filter had a good retention efficacy for Brett. GF filters are depth filters recommended for use prior to membrane filtration.
-All PES filters had a very good retention of Brett cells with no culturable Brettanomyces cells detected in growth media after filtration. PES filters are membrane filters recommended for use after pre-filters in order to ensure microbial stability.

Significance of the study:
The study indicates that the composition of the filters in addition to micron size determine whether or not it will have a good retention ability for Brett. Micron size alone cannot be an indication. This is an important finding for winemakers in terms of filtration before bottling, as well as scientists doing research on 
Brettanomyces.

Reference:
Filomena L. Duarte, Luis Coimbra, Margarida Baleiras-Couto (2017). Filter media comparison for the removal of Brettanomyces bruxellensis from wine. Am J Enol Vitic. October 2017 68: 504-508; published ahead of print June 22, 2017 ; DOI: 10.5344/ajev.2017.17003

Image copyright: Shutterstock

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