The impact of non-Saccharomyces inclusion during alcoholic fermentation on rosé wine colour density and stability

Abstract

Rosé wine popularity is mostly due to its pink colour which results from grape pigments. Varying from a pale salmon to a deeper pink colour, its stability and intensity are not as good as the those of red wines, it’s therefore crucial to improve them. Yeasts, responsible for alcoholic fermentation, have been shown to influence wine colour, in particular when nonSaccharomyces (NS) yeasts are inoculated alongside Saccharomyces cerevisiae. This study investigates the impact of NS yeasts inclusion on the colour density and stability of rosé wine.

A two phase experiment was conducted using rosé wine made in the lab. The first phase screened forty-three NS yeast strains under two fermentation conditions: in co-inoculation with S. cerevisiae and in sequential inoculation where S. cerevisiae was added 48h after the NS yeasts. The ability to finish fermentation varied among strains with lower success rates for yeasts from the Pichia genus. Five yeasts significantly influenced the wine coulour intensity and stability and were selected for a second experiment. This second phase required scaling-up the fermentations which were carried out under three conditions: co-inoculation, sequential and mono-inoculation of the NS yeasts. A post-fermentation accelerated ageing step was also added for the wine. To analyse the colour intensity and stability of the wines the modified Somers assay was used.

The findings revealed that NS yeasts have a great potential to improve colour stability, also after ageing, but this is highly strain-dependent. The impact on colour intensity was not as important as expeected. These results suggest that NS yeasts could be a crucial tool to modulate rosé colour stability in the future. Further research is required to elucidate molecular mechanisms behind the influence of these yeasts on colour and optimise it for comercial purposes.

Popular Abstract

Fifty Shades of Rosé or how yeast shapes wine colour

Why do people love drinking rosé? Its beautiful pink colour combined with its delicious freshness is attractive, fun and it does not feel like you need to be a wine expert to enjoy it. It is just an easy wine that is pink! This colour comes from natural grape pigments. In fact, these are the key elements which make a paler or deeper rosé colour, it even impacts the stability. During wine fermentation, the use of yeasts can impact these pigments and thus the colour. Specifically, uncommon yeasts (NS yeast) can be combined with the most used one (S. cerevisiae) to reach different colour outcomes. This research explored the potential of these yeasts to affect the colour intensity and stability of rosé.

To investigate this, we made wine using three different fermentation approaches: 1) the NS yeasts were fermented in the grape juice with S. cerevisiae at the same time, 2) S. cerevisiae was added 48h after the NS yeasts, 3) the NS yeasts were fermented alone in the grape juice. Once the wine was finished, we used a technique called the modified Somers assay to break down the wine colour in different components. This method showed us how much red or yellow/brown pigments were present as well as how stable the colour was.

For the screening part, we tested 43 NS yeasts in conditions 1 and 2. The fermentation success varied between the different yeast combinations. Particularly, yeasts from the Pichia family struggled to complete fermentation. This screening revealed that NS yeast combined with S. cerevisiae clearly altered wine colour. We selected 5 promising NS strains for the second part of the experiment.

For this second part of the study, we scaled-up to more winemaking-like conditions and simulated ageing conditions by putting the samples in a hot room. The 5 yeasts were tested in conditions 1,2 and 3. The main takeaway from this part was that the impact on wine colour was highly dependent on the NS yeasts and the fermentation method. Some NS yeasts increased the colour intensity and boosted red pigments while others led to more browning. Notably, it seemed that most combinations increased colour stability even when aged.

These findings suggest that using NS yeast could be a strategy to modify rosé colour and help preserve its signature pink colour over time. While we need to run more experiments to understand the actual interplay between the different yeasts and wine colour, these first findings open cool possibilities for winemakers to explore different pink shades of rosé and create more long-lasting colours.

Master’s Degree project in Molecular Biology MOBM02, 30 credits

Supervisor: Rebecca Deed
School of Chemical Sciences, the University of Auckland, New Zealand
Department of Biology, Lund University

• author: Falcotet, Madeline
• supervisor: Rebecca Deed
• organization: Degree Projects in Molecular Biology
• course: MOBM02 20242
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9188142
• date added to LUP: 2025-05-07 15:19:47
• date last changed: 2025-05-07 15:19:47