The higher alcohols 2-phenylethanol, tryptophol, and tyrosol are a group of yeast-derived compounds that have been shown to affect the aroma and flavour of fermented beverages. Five variants of the industrial wine strain AWRI796, previously isolated due to their elevated production of the ‘rose-like aroma’ compound 2-phenylethanol, were characterised during pilot-scale fermentation of a Chardonnay juice. We show that these variants not only increase the concentration of 2-phenylethanol but also modulate the formation of the higher alcohols tryptophol, tyrosol, and methionol, as well as other volatile sulfur compounds derived from methionine, highlighting the connections between yeast nitrogen and sulfur metabolism during fermentation. We also investigate the development of these compounds during wine storage, focusing on the sulfonation of tryptophol. Finally, the sensory properties of wines produced using these strains were quantified at two time points, unravelling differences produced by biologically modulating higher alcohols and the dynamic changes in wine flavour over aging.
Background and Aims: Winemakers utilise various remediation strategies for decreasing 'reductive' characters in wine. Remediation strategies, such as the addition of diammonium phosphate (DAP) during fermentation, copper fining, the addition of fresh lees or lees products to wine, and aeration of the must during and after fermentation, are commonly employed in an effort to prevent the formation or to remove undesirable volatile sulfur compounds. In this study, the relative effectiveness of five strategies for remediation of 'reductive' aroma was compared in a Shiraz wine. Methods and Results: At the onset of the development of 'reductive' aromas during Shiraz fermentation, each ferment was treated with a unique remediation strategy: DAP addition; macro-oxygenation; copper fining; a combination of macrooxygenation and copper fining; or the addition of fresh lees from a donor wine. While a relatively small difference in volatile sulfur compounds was found between treatments, copper fining, lees and DAP addition produced wines with elevated 'reductive' characters at certain time-points post-bottling; while macro-oxygenation or macro-oxygenation with copper produced wines with a low sensory score for 'reduction'-related attributes. Conclusions: Macro-oxygenation during fermentation was the most effective remediation strategy. Lees addition, and to a lesser extent, copper fining and DAP addition, diminished fruit attributes and produced wines with noticeable 'reductive' characters. Significance of the Study: Macro-oxygenation during fermentation produced wines with the lowest 'reduction'-related attributes while enhancing 'fruity' attributes. This work also highlighted the compositional effects of each type of remediation treatment.
Background and Aims The use of non‐Saccharomyces yeast strains as starter cultures for wine production has become increasingly popular, particularly due to their positive effect on wine composition, colour, aroma and flavour. Here, we characterise the volatile aroma composition and the sensory profile of Shiraz and Cabernet Sauvignon wines produced with novel active dry yeast preparations of Metschnikowia pulcherrima compared to that of reference strains. Methods and Results Winemaking treatments included an uninoculated fermentation, two reference Saccharomyces cerevisiae fermentations, and sequential fermentations inoculated with either M. pulcherrima AWRI1149 or M. pulcherrima AWRI3050 and S. cerevisiae. Amplicon‐based internal transcribed spacer phylotyping was used to determine microbial population dynamics during fermentation. Wines were analysed for volatile composition and subjected to sensory analysis. The M. pulcherrima strains survived and dominated in both grape cultivars, and produced distinctive wine volatile profiles depending on the inoculation treatment. These differences in volatiles resulted in significant differences for several sensory attributes. Conclusions Wines made with active dry yeast preparations of M. pulcherrima AWRI1149 and M. pulcherrima AWRI3050 were characterised by increased intensity of desirable sensory attributes and by low scores for negative descriptors. Significance of the Study This work provides winemakers with additional yeast preparations that can shape sensory profile and wine style.
Changes to Australian regulations now allow the limited addition of water to high-sugar musts pre-fermentation. In light of these changes, this study explored how water addition affects Shiraz wine composition and sensory properties. Wines were made from grapes at ≈13.5, 14.5 and 15.5° Baume. Water was added to musts from the ripest fruit by direct addition, or by using a juice substitution (run-off and replace) approach. To compare the effect of juice run-off independently, saigneé treatments were included. Wines made from the fruit that was harvested earlier generally had a lower “opacity” and higher “red fruit” aroma as the defining sensory attributes. Undiluted wines made from riper fruit had higher phenolics, and were characterised by “dark fruit” and “dried fruit” attributes, and “spice”, a “brown colour” and “opacity”. These attributes were accentuated in wines from the same fruit which received saigneé treatments and reduced in all of the water addition treatments. In particular, higher levels of water addition without juice substitution increased the “cooked vegetable” and “drain” attributes in the wines. This indicates possible negative effects of larger water additions, such that a low to moderate adjustment in Shiraz winemaking is suggested.
In most yeast-driven biotechnological applications, biomass is separated from the aqueous phase after fermentation or production has finished. During winemaking, yeasts are removed after fermentation by racking, filtration, or centrifugation, which add costs to the overall process and may reduce product yield. Theoretically, clarification and filtration can be aided through use of yeast strains that form flocs due to cell-cell binding, a process known as flocculation. However, because early flocculation can cause stuck/sluggish fermentations, this phenotype is not common amongst commercially available wine yeasts. In this study we sought to identify wine strains that exhibit late-fermentation flocculant behaviour using two complementary approaches; a high-throughput sedimentation rate assay of individual strains and a competitive sedimentation assay using a barcoded yeast collection. Amongst 103 wine strains, several exhibited strong sedimentation at the end of the wine fermentation process under various environmental conditions. Two of these strains, AWRI1688 and AWRI1759, were further characterised during red winemaking trials. Shiraz wines produced with both strains displayed improved filtration-related properties. AWRI1759 produced wines with greater filterability, whereas AWRI1688 enabled the recovery of larger wine volumes after racking. Thus, this study demonstrates the effective use of sedimentation screening assays to identify wine yeasts with practical winemaking applications.
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