Filomena L. Duarte1, Luís Coimbra2, Margarida Baleiras-Couto1
1Instituto Nacional de Investigação Agrária e Veterinária, INIAV – Dois Portos, Quinta da Almoínha, 2565-191 Dois Portos, Portugal 2Multifiltra – Filtração e Equipamentos Industriais, Lda., 2735-003 Cacém, Portugal
The presence of Brettanomyces bruxellensis is of great concern for wine producers due to off-flavour production, particularly 4-ethylphenol and 4-ethyl guaiacol, as well as tetrahydropyridines, acetic acid, ethyl acetate and isovaleric acid.
One of the available tools for eliminating contamination with these yeasts is filtration. Suarez et al. (2007) stated that effective removal of Brettanomyces cells is achieved using membranes with a pore size smaller than 0.45 μm.
In the present work, different filtration media, which differ in terms of composition and micron rating, were compared for the efficacy of B. bruxellensis removal from wine.
The FDA Guidelines on aseptic processing, which are intended to provide a margin of safety well beyond what would be expected in wine production, were followed. In agreement, over 107 cel/cm2 filter surface are needed. Brettanomyces cells (ISA 1791) pre-adapted to wine (alcohol 6 % v/v) were transferred to a 12 % (v/v) red wine 24 h before the assay.
Filtration procedures are illustrated in the following photos:
The filtering discs (Amazon Filters) were of different media: borosilicate glass microfiber (X, V), polypropylene (PP 0.6 and PP 1.0 m) and polyethersulphone (PES) (0.45, 0.65, 1.0 m) and of different production lots, whenever possible.
Filter removal capacity was evaluated by plate counting (1 and 50 mL) of filtrated wine in YPD with bacteria and filamentous fungi inhibitors. Some samples were also incubated in solid and liquid Dekkera/Brettanomyces differential medium (DBDM) to reinforce the results.
Yeast counts were performed to the wine before (Vi) and after (VB) Brettanomyces addition. No colonies were detected in Vi. VB yeast count was 3.4×106 cfu/mL well above the required 1.6×106 cel/mL.
The V grade borosilicate glass microfiber filters showed low retention (lower than 104) of B. bruxellensis, while X grade presented high retention efficacy, as no cells were detected in the filtrated wine analysed.
Polypropylene filters showed poor efficacy as colonies were too numerous to count. However, visual comparison of counting plates revealed lower number of cfu in PP 0.6 filtered wine.
Using polyethersulphone filters PES 1.0, PES 0.65 and PES 0.45 (two lots and respective duplicates) no B. bruxellensis cells were detected in the filtrated wine analysed. DBDM incubations confirmed the absence of growth.
PES filters showed high B. bruxellensis removal efficacy in all micron rating tested. Similar efficacy was achieved for X grade borosilicate glass microfiber filter. On the opposite, low retention was obtained with polypropylene and V grade borosilicate glass microfiber filters.
Different filter composition with similar micron rating showed different retention of B. bruxellensis, highlighting the relevance of filter media on removal mechanisms. Accordingly, it is crucial that reports on Brettanomyces removal by filtration fully characterize filtration media, apart from pore size value.
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Amazon Filters will be exhibiting alongside one of their main distributors Suminisitros Multifiltra at the ENOMAQ exhibition, from the 15th till the 17th of February 2017. The International Show of Winery, Bottling Machinery and Equipment which will offer a platform to discover latest technologies, current market trends, and many other advances of the industry.
The filter media evaluation discussed above will be exhibited at the ENOMAQ show, representatives on the stand will be happy to discuss this information as well as answering any questions.
For more information on where to find us, see the exhibition website.
We would also like to add a special thank you to everyone involved in carrying out the evaluation and constructing this paper.
- Suárez, J.A. Suárez-Lepe, A. Morata, F. Calderón (2007) The production of ethylphenols in wine by yeasts of the genera Brettanomyces and Dekkera: A review. Food Chem. 102: 10–21