Co-flocculation of Saccharomyces cerevisiae and Non-Saccharomyces Yeast Species to Increase Colour Intensity in Pinot noir Wines

Abstract

Vitis vinifera L. cv. Pinot noir is New Zealand’s most important red grape variety and second most planted variety after Sauvignon blanc. Pinot noir is a notoriously difficult grape to work with – in the vineyard it is susceptible to disease and climatic changes, and in the winery, it is a challenge to extract the compounds responsible for colour and then ensure colour stability during aging. The appearance of a wine, of which colour is a crucial component, can shape a consumer’s enjoyment and perception of flavour while drinking it. Research has shown that consumers prefer deeper colour in red wines and therefore the development of tools to achieve greater colour intensity in Pinot noir wines could be extremely useful for winemakers and the wine industry.

This research explores the impact of interspecies yeast flocculation and sequential inoculation on Pinot noir colour. Six commercial non-Saccharomyces yeast species, LAKTIA (Lachancea thermotolerans), CONCERTO (Lachancea thermotolerans), GAÏA (Metschnikowia fructicola), FROOTZEN (Pichia kluyveri), BIODIVA (Torulaspora delbrueckii) and PRELUDE (Torulaspora delbrueckii), and two commercial Saccharomyces cerevisiae strains, VL3 and RC212, were used in microfermentations of synthetic grape must, both individually and in every possible combination of non-Saccharomyces and S. cerevisiae. Sedimentation rate assays at the end of fermentation were performed to determine how well each individual yeast, and yeast combination, flocculated. The most flocculant individual yeast was BIODIVA and the most flocculant S. cerevisiae and non-Saccharomyces pairings were VL3 + BIODIVA and RC212 + BIODIVA, suggesting that mixed species flocs may have formed.

These yeast combinations, along with S. cerevisiae controls of VL3 and RC212 alone, were used in a 20 L-scale Pinot noir winemaking trial. Both UV/visible spectrophotometric measurement of colour intensity, and sensory evaluation of wine appearance performed by human participants, found that the mixed species fermentations resulted in wines with greater colour intensity compared to the controls. The final VL3 + BIODIVA wines were found to be deeper in colour than the VL3 control wines and while the final RC212 + BIODIVA wines were not found to be different from the RC212 control wines, the control juice used at the beginning of the experiment was significantly deeper in colour intensity than the juice used for the sequential inoculations.

Two methods of measuring anthocyanins in the wines, the Adams-Harbertson assay and high performance liquid chromatography (HPLC), confirmed that the mixed fermentation wines with higher colour intensity, had lower anthocyanin concentrations than the less intense control wines, despite anthocyanins being the principal source of colour in young red wines. This result is likely due to the phenomenon of copigmentation, which can result in wines displaying a deeper colour intensity than would be expected based on their anthocyanin content. The increases in colour intensity may be due to increased flocculation during primary fermentation, between the highly flocculant BIODIVA and the two strains of S. cerevisiae. A further trial found that the non-Saccharomyces yeast strains used in the sedimentation rate trial adsorbed significantly more pigments from Pinot noir skins than the S. cerevisiae strains, with BIODIVA adsorbing the most. Grape pigments are adsorbed onto yeast cell wall mannoproteins and previous research has suggested that BIODIVA and other strains of T. delbrueckii have a high concentration of mannoproteins compared to other yeast species. Given that flocculant yeasts have differences in cell wall mannoprotein composition compared to non-flocculant yeasts, the cell wall could be a crucial component behind the mechanism involved in the greater colour intensity of wines inoculated with BIODIVA. Further research is required to confirm this hypothesis and confirm that flocculation is the cause of colour intensity changes or if there is another aspect of BIODIVA metabolism or mixed species interactions resulting in enhanced colour intensity and copigmentation, such as increased production of acetaldehyde or pyruvic acid.

This work expands on recent studies exploring the benefits of sequential inoculation and yeast flocculation and the relationship between yeast behaviour and red wine colour. There are multiple avenues for future research to refine our understanding of mixed-species interactions, including co-flocculation, between yeast species and uncover the mechanisms responsible for the impact of sequential inoculations and flocculation on red wine colour, in particular for Pinot noir, but with further application for other red wine styles.