The breeding of yeast strains for novel oenological outcomes

[摘要] The quality of wine is influenced by a variety of factors, most noticeably the quality ofthe grapes, winemaking practices and the yeast strains used for alcoholic fermentation.Although several yeast strains are present in the must at the beginning of fermentation,strains of S. cerevisiae quickly dominate and survive alcoholic fermentations. Thisdominance of S. cerevisiae prompted research that led to the development of amultitude of industrial yeast starter cultures. Starter cultures are usually capable of quickand complete fermentations, with minimal production of deleterious substances such asvolatile acidity, H2S, SO2 and ethyl carbamate. Yeast strains should be able to survivethe stressful environment created during alcoholic fermentation, whilst possibly offeringnovel oenological benefits such as pectinolytic activity, killer activity and malic aciddegradation. The increased production of volatile esters and higher alcohols may alsobe desirable, as this will allow the production of wines that are more aromatic.In this study, VIN13 was crossed with S. paradoxus strain RO88 and WE14 by using amicomanipulator. VIN13 was chosen for its fast and complete fermentation ability andmoderate aroma production potential. Other factors such as the presence of killeractivity and low production of volatile sulphur compounds also favoured the selection ofVIN13. S. paradoxus strain RO88 was selected for its ability to degrade malic acid andthe favourable impact on aroma production during fermentation. Hybrids between theseyeasts may have the potential to produce more aromatic wines, with the added bonus ofpectinolytic activity and a strong fermentation capacity. The first crossing yielded 5hybrids between VIN13 and S. paradoxus strain RO88. Two of these hybrids stood outin the sense that they were able to degrade more malic acid than VIN13 and they alsopossessed killer and pectinolytic activity. Cinsaut wine was made and the 2 hybridswere shown to have higher aroma compound capacity than the parental yeasts. Thiswas also confirmed during sensory evaluation. The second crossing between VIN13and WE14 yielded 10 hybrids with low H2S production potential and killer activity. WE14was selected for its ability to produce very aromatic wines and also the slowerfermentation capacity. Hybrids between these yeast may have the potential to producewines with an increased aromatic content and the fermentation rate might be slower,thereby improving the aroma profile of the wine. After microvinification, 5 hybrids wereselected on the basis of fermentation rate differing from that of the parental yeasts andfavourable oenological traits, such as fast and complete fermentation, high production ofglycerol and low production of volatile acidity. Pinotage wine was made and it wasshown that some of the hybrids produced more esters and higher alcohols than theparental yeasts. Sensory evaluation also showed the aroma production potential of thehybrids, as some of the hybrids were shown to score higher for banana, cherry andtobacco characteristics.

[发布机构] Stellenbosch University