The aim of the study was to evaluate the use of S. japonicas for winemaking.
· S. japonicus was compared with Saccharomyces cerevisiae Lalvin EC 1118 in free form, in immobilised form, in co-inoculation with EC 1118 (free and immobilised) and in sequential inoculation, where EC 1118 was inoculated 48 hours after immobilised S. japonicas.
· Fermentations were conducted at 22°C in 500 mL Erlenmeyer flasks containing 350 mL Trebbiano juice.
· Viable yeast count, wine protein stability and volatile compounds were measured.
· The fermentation speed of EC 1118 was negatively affected only in the sequential fermentations where it was inoculated 48 hours after S. japonicas inoculation.
· S. japonicas flocculated after the second day of alcoholic fermentation when it was used in the non-immobilised form.
· S. japonicas consumed a lower amount of ammonia and amino acids than EC 1118 as a result of arrested cell growth due to stressful fermentation conditions.
· In the co-inoculated fermentations with the immobilised S. japonicas, lower final alcohol concentrations were observed. Encapsulation of S. japonicas seems to protect it from ethanol toxicity, making it more metabolically active during co-fermentation.
· S. japonicas can form volatile acidity and formed the highest concentrations (0.76 g/L) when it was used in a non-immobilised form in a pure culture fermentation. In the immobilised pure culture fermentation it formed 0.34 g/L volatile acidity.
· S. japonicas did not ferment to dryness in the pure culture fermentations and formed on average 10.79% and 11.22% alcohol for non-immobilised and immobilised fermentations respectively.
· Partial degradation of malic acid by S. japonicas was observed and the biggest effect was found in sequential inoculation, indicating S. cerevisiae (EC 1118) growth suppressed malic acid breakdown.
· In pure culture fermentations S. japonicas produced twice the amount of glycerol than EC 1118, but this effect was not seen in co- and sequential inoculation.
· S. japonicas formed increased higher alcohols and acetate esters compared to EC 1118, especially ethyl-acetate, which have a solvent-like character when present in concentrations above 150 mg/L. However, in the co-inoculated and sequential fermentations the ethyl-acetate concentrations were below the negative sensory threshold for the compound.
· No H2S was detected for the S. japonicas strains when plated out on Biggy Agar and no volatile sulphur compounds were detected by an informal sensory evaluation of the wines.
· S. japonicas was observed to release a high quantity of polysaccharides into the grape juice medium and the concentration of polysaccharides were inversely related to the turbidity measurements after the Bentotest and the Proteotest.
Significance of the study
The study was conducted on small scale, but initial results indicate that S. japonicas has interesting characteristics of potential oenological importance. This study also focussed on chemical analyses only and future larger scale studies that include wine sensory analysis can shed more light on the potential use of S. japonicus starter cultures. Of all the results obtained the lower alcohol concentrations observed when using immobilised S. japonicas in co-inoculation with S. cerevisiae seems the most promising.
Paola Domizio, Livio Lencioni, Luca Calamai, Lorenzo Portaro, Linda Bisson. Evaluation of the Yeast Schizosaccharomyces japonicus for Use in Wine Production. Am J Enol Vitic. April 2018: ajev.2018.18004; published ahead of print April 23, 2018 ; DOI: 10.5344/ajev.2018.18004