Ferments: 3 intriguing experiments

Improving red wines by adding white wine lees

Researchers in Bordeaux have added freeze-dried lees from white wines to red wines to stimulate the growth of lactic acid bacteria (LAB) and to promote malolactic fermentation (MLF). They also evaluated the risk of spoilage linked to the addition of wine lees by analysing their impact on the growth of Brettanomyces bruxellensis, and they analysed their impact on aromatic compounds.
The study, published here and in the International Journal of Food Microbiology, shows the wine lees – a known source of nutrients that can be used for stimulating the growth of microorganism by introducing nitrogenous compounds – enhanced Oenococcus oeni growth and MLF performance in both a wine-like medium (WLM) and ‘natural wine’, finishing MLF after 12-15 days. In addition, they enabled the completion of MLF in the wines with a low bacterial population, in which MLF was not completed when wine lees were not added.
The report also suggests freeze-drying could be a suitable tool for preserving and storing wine lees. Frozen lees are easier to dose compared to fresh liquid wine lees. In this study, the added concentrations of wine lees were 0.25g/L and 0.5g/L, which correspond to 25g/hL and 50g/hL respectively – concentrations like those of other oenological preparations used as activators for alcoholic fermentation or MLF. “The use and concentrations of wine lees proposed in this study can therefore be easily adapted to an industrial application,” the report states.
The effect of wine lees on the WLM was also tested at lower inoculation ratios: 102 and 104 cells/mL. The results showed that it is possible to reduce the quantity of starter culture needed to inoculate a wine before MLF, mainly when using the highest tested wine lees concentration (0.5 g/L).
Regarding the effect on wine aromas, the study found that by the end of MLF (in wine samples with or without wine lees treatment) the concentrations of several esters had increased significantly. Some ester concentrations increased after MLF due to LAB metabolism. Furthermore, some others also significantly increased in concentration compared to those in the wine without added wine lees; for example, ethyl 2-methylpropanoate, ethyl 2-methylbutanoate and ethyl 3-methylbutanoateare in Merlot and 2-methylpropyl acetate in Petit Verdot. “These results suggest that white wine lees addition could have a positive impact on these short- and branched-chain alkyl fatty acid esters, because they are known to contribute highly to increasing the perception of fruity aromas,” say the researchers.

Impact of lees on Brettanomyces bruxellensis growth

B. bruxellensis growth in wine can reduce wine quality due to the resulting production of volatile phenols. Thus, it was important to address the effect of wine lees on B. bruxellensis growth. Two different pasteurised wines with and without added lees were inoculated with approximately 102-103 CFU/mL of three B. bruxellensis strains. “The results show that they did not promote the growth of B. bruxellensis in wine,” according to the report.
The conclusion is: “The study found there is no potential microbial spoilage risk linked to their use and the aromatic quality of the wine is not compromised.”

Using non-Saccharomyces yeast for in-bottle ferments

In Italy’s Emilia region, researchers have been adding two non-Saccharomyces to a commercial strain of Saccharomyces cerevisiae yeasts for the secondary in-bottle fermentation of Lambrusco wines.
This is interesting because non-Saccharomyces strains can decrease the rate of fermentation, increase mouthfeel by releasing mannoproteins, and improve the wine’s aromatic profile thanks to overexpressed enzymatic activities.
The new study, published in Oeno One Vol. 58 No. 3 (2024), used the Hanseniaspora guilliermondii and Torulaspora delbrueckii strains for the experiments on two classic-method Lambruscos, made from Lambrusco sorbara and Lambrusco marani.
T. delbrueckii have been involved in fermentation with S. cerevisiae in winemaking since the 1990s, when its positive contribution to the aromatic profile of wine and its ability to maintain biological activity at low temperatures were highlighted. Recent studies have confirmed its preference for low fermentation temperatures and noted ethanol resistance up to 18%.
The use of Hanseniaspora spp in winemaking is less widespread, but its enzymatic pathway is broad and of great interest in terms of impact on the volatile profile of wines. An ethanol resistance of up to 12.5% suggests it could also work in sparkling wine production.
The results of the new study show:

• The survival rate of these two non-Saccharomyces strains was comparable with that of S. cerevisiae (at least 12 days).
• Mixed fermentations show an initial delay, compared to fermentations performed by pure S. cerevisiae.
• The simultaneous presence of two yeast species reduced the maximum fermentation rate, without any relevant alteration in the main oenological parameters (acidity, acetic acid, pressure, and alcohol) of resultant wines.
• Bottle fermentation by ordinary S. cerevisiae enhances the contribution of acetates in the wine profile, while the presence of non-Saccharomyces yeast resulted in wines characterised by floral and spicy aromas, typical of higher alcohols and fatty acids.

The researchers concluded: “Bottle fermentation influences the aromatic profile of Lambrusco wines, without depletion of molecules that could be related to the distinctive traits of each grape variety. The wine obtained with a pure culture of S. cerevisiae appeared to be a transition point, in terms of organoleptic profile, between the base wine and the bottle-fermented Lambrusco obtained by mixed yeast cultures. Further studies will be necessary to establish whether these variations in the aromatic profile are due to an effective contribution of non-Saccharomyces yeasts or the altered behaviour of Saccharomyces, due to a competition between different species.”

Yeast derivatives: a double-edged sword

Using yeast derivatives (YDs) to enhance the quality of white wine could increase the likelihood of defective aromas, according to another recently published study from Italy.
YDs – commercial products obtained from yeast colonies grown in bioreactors then inactivated and dried – are employed in winemaking to supply nitrogen (N), stimulate yeast growth, prevent stuck fermentations, and remove unwanted compounds.
But one serious wine aroma defect – atypical ageing (ATA), a sensory defect that occurs in young white wines and is described as a loss of varietal aroma and the advent of unpleasant notes reminiscent of naphthalene, dirty cloth and acacia – is known to come from the oxidation of indole-3-acetic acid (IAA) to 2-aminoacetophenone (AAP). As IAA is one of the main plant hormones and YDs are often manufactured using material of plant origin, it can be assumed that AAP precursors are contained in those commercial formulations. If this is the case, the use of YDs could potentially increase the risk of tainted wines.
To explore this hypothesis, 28 commercially available YDs were screened for the presence of AAP-related compounds, as well as their amino acidic content. Since several ATA precursors were detected, fermentation experiments were carried out in which different amounts of YD were added to different grape musts. Interestingly, depending on the nature of the commercial formulation, AAP development was observed to be either enhanced or reduced. The researchers hypothesise that, as well as the AAP and ATA precursors contained in the commercial formulation, the presence of other compounds, such as cell walls, might exert an adsorption effect, thus affecting the AAP content in the finished wine.
Furthermore, as diammonium phosphate (DAP) is also used to provide grape must with N, the effect of supplementing must with DAP was investigated. The addition of increasing amounts of DAP (up to 400mg/L) did not significantly affect the accumulation of AAP.
The study, published in OENO One Vol. 58 No. 2 (2024), concludes by saying: “A better understanding of the relationship between the raw material used in YD production and the ATA-precursors contained in the commercial products could aid in manufacturing products less likely to develop sensorial defects. Moreover, given their important role in the onset of ATA, the physio-chemical attributes of YDs should also be thoroughly studied.”