S. CEREVISIAE AND O. ŒNI BIOFILMS FOR CONTINUOUS ALCOHOLIC AND MALOLACTIC FERMENTATIONS IN WINEMAKING

Abstract

Biofilms are sessile microbial communities whose lifestyle confers specific properties. They can be de-fined as a structured community of bacterial cells enclosed in a self-produced polymeric matrix and adherent to a surface and considered as a method of immobilisation. Immobilised microorganisms offer many advantages for industrial processes in the production of alcoholic beverages and specially increasing cell densities for a better management of fermentation rates. Controlling the speed of alcoholic (AF) and malolactic (MLF) fermentations in wine can be an important challenge for the production of certain short rotation wines for entry-level market segments.

The objective of this work was to design a continuous winemaking process using yeasts and bacteria biofilms. In a first part we showed the possibility of inducing the adhesion and biofilm formation by O. œni and S. cerevisiae separately, in low nutriment medium, on different materials already used in the winery environment. Then the biofilm formation was implemented in a 250 ml continuous bioreactor system for both microorganisms. At the end of the biofilm formation step, quantities of attached biomass (CFU counts) were close for all materials and over 5 log (UFC/cm²) for S. cerevisiae, over 6.2 log (UFC/cm²) for O. œni.

For continuous fermentations the inoculated supports were used in a similar 250 ml bioreactor with 3 different modalities: alcoholic fermentation (AF) by S. w in grape must, or Malo-Latic Fermentation (MLF) by O. oeni in wine or, co-fermentation (simultaneous AF and MLF) with both species biofilms feeded with grape must. The progress of the continuous fermentations was analysed. Over periods of 3 to 4 weeks under a continuous regime with a 48h residence time, stable consumption rates of 4 g/l/h for glucose + fructose and 1,8 g/l/24h for L-malic acid were reached in co-fermentations.

This biofilm continuous reactor could be the first step towards perfectly controlled industrial winemaking processes.