Influence of wood chips addition during alcoholic fermentation on wine phenolic composition

INTRODUCTION: Foam stability of sparkling wines is significantly favored by the presence of surface active agents such as proteins and polysaccharides [1]. For that reason, the renowned sparkling wines are aged after the second fermentation in contact with the lees for several months (even years). Thereby wines are enriched in these macromolecules due to yeast autolysis. Since this practice is slow and costly, winemakers are seeking for alternative procedures to increase their concentration in base wines. In that sense, the supplementation with inactive yeast during alcoholic fermentation has been proposed [2]. The aim of this study was to determine whether this new strategy is really useful for enriching base wines in macromolecules and for improving foam properties of the base wines.

Fungal bunch rots of grapes cause major losses to grape yield worldwide, yet the impact these moulds have on grape and wine quality is not well characterised. We sought to investigate the formation of unwanted volatile compounds of fungal origin in both synthetic grape juice culture media and in inoculated grape berries. Botrytis cinerea, Aspergillus niger, Aspergillus carbonarius, or Pencillium expansum were grown in synthetic grape juice medium and the culture homogenates analysed 4 and 7 days post inoculation. HS-SPME-GC-MS analysis of the culture homogenates 4 days post inoculation demonstrated that each of the fungi examined produced varying quantities of the mushroom or fungus-like aroma compounds, 1-Octen-3-ol, 1-Octen-3-one and 3-Octanone with A. carbonarius producing up to ten times the amounts of all three metabolites per mg of dry mycelium.

Nitrogen is an important nutrient of yeast and its low content in grape must is a major cause for sluggish fermentations. To prevent problems during fermentation, a supplementation of the must with ammonium salts or more complex nitrogen mixtures is practiced in the cellar. However this correction seems to improve only partially the quality of wine [1]. In fact, yeast is using nitrogen in many of its metabolic pathways and depending of the sort of the nitrogen source (ammonium or amino acids) it produces different flavor active compounds. A limitation in amino acids can lead to a change in the metabolic pathways of yeast and consequently alter wine quality.

The Ability of PVPP (Polyvinylpolypyrrolidone), PVP-DEGMA-TAIC (copolimerization of N-vinyl-2-pyrrolidinone with ethylene glycol dimethacrylate and triallyl isocyanurate) and PAEGDMA
(poly(acrylamide-co-ethylene glycol dimethacrylate)) polymers was tested as removal agents for Fumonisin B1 (FB1) and Fumonisin B2 (FB2) from model solutions and red wine. The polymers removal capacity was checked at three different resident times (2, 8 and 24 hours of contact time between the polymer and the sample), showing no differences in the percentage of FB1 and FB2 removal. Then, different polymer concentrations (1, 5 and 10 mg mL-1) were tested in model solution with and without phenolics (i.e. gallic acid and 4-methylcatechol).

The aromas found in young Bordeaux red wines made with Merlot and Cabernet Sauvignon suggest a complex mixture of aromas of fresh red fruits such as cherry or blackberry for Merlot, and strawberry or blackcurrant for Cabernet Sauvignon. The aromas of these wines are closely linked with the maturity of the grapes. The climate change that has occurred during the last decade in Bordeaux has induced changes in the ripening conditions of grape berries. It is now widely admitted that over-ripening of the berries during hot and dry summers results in the development of characteristic flavors reminiscent of cooked fruits (fig, prune). The presence of these overriding odors found in both musts and young wines affects the quality and subtlety of the wine flavor and may shorten its shelf life.