Novel winemaking practices to accelerate autolysis and improve composition and foaming properties of sparkling wine

Aged wine or 'autolytic' character is a hallmark in premium sparkling wine usually resulting from traditional method (Methode Traditionelle) winemaking. Sparkling wine made by this method develops the distinct and desirable flavour and aroma profile and bubbles, attributed to proteolytic processes during prolonged ageing on lees after the secondary fermentation. Intrinsic to this aged wine character is natural enzymatic decomposition of yeast (autolysis) that facilitates the release of compounds into wine that influence wine aroma, flavour and effervescence. The production of high quality sparkling wine is expensive, both in terms of time and physical resources, and there is an opportunity to improve not only the quality of premium sparkling wine but also that of the lower cost sparkling wine options for the consumers, through a combination of traditional practices and innovation. In an effort to introduce 'autolytic' character into sparkling wine sooner, microwave, ultrasound or addition of b-glucanase enzymes were applied to yeast to accelerate the disruption of Saccharomyces cerevisiae cell walls. These treated yeasts were added to the tirage liquor during secondary fermentation, and wines analysed at 6 monthly intervals. Treatments applied produced features on yeast that were distinct from that of the untreated control yeast. Whilst control yeast displayed budding cells (growth features) with smooth, cavitated and flat external cell appearances; microwave treated yeast cells exhibited modifications like 'doughnut' shapes immediately after treatment (time 0). Similar 'doughnut'-shaped and 'pitted/porous' cell features were observed on progressively older lees from the control. Flow cytometry interpreted alongside the scanning electron microscopy images of yeast revealed bimodal populations of yeast cells with low and high propidium iodide intensities and distinctive 'doughnut'-shaped cell features observed in association with the microwave treatment only at tirage, that were not observed until 12 months wine ageing in older lees from the control. From a quality perspective, 18 months bottle age was optimum in sparkling wine production on the basis of the influence of yeast treatments added to the tirage solution to effect enhancement of protein concentration, amino acids, polysaccharides and lipids, and the impact of these compounds on sparkling wine foam volume and stability. The microwave and b-glucanase enzymes treatments were associated with a 10 % increase in total free amino acid concentration and a 10 % increase in proline content between 6 months and 18 months bottle age in Chardonnay/Pinot noir blend sparkling wines, confirming disruption effects observed in the visualisation studies. Microwave treatment was associated with elevated asparagine content at 18 months bottle age. The b-glucanase enzymes and ultrasound treatments were associated with significant accumulation of total lipids, that were driven by 2-fold increases in the phospholipids and monoacylglycerol components, respectively, in wine at 18 months bottle age and further the microwave treatment was associated with significantly elevated triacylglycerol at 18 months bottle age. General responses to wine ageing included 60 % higher total phenolic concentration of older sparkling wines than younger wines, and increased total protein concentration from 6 months to 12 months bottle age. In monovarietal sparkling wine production, Chardonnay wines yielded 4-fold higher total protein concentration compared to Pinot noir wines. Total protein concentrations decreased by 40 % in both Chardonnay and Pinot noir sparkling wines from 18 months to 24 months bottle age. Microwave treatment or ultrasound treatment enhanced total protein concentrations by 15 % in Pinot noir sparkling wines aged to 18 months on lees compared to 24 months on lees. Storage of Chardonnay wines at 25 °C depleted total protein concentration by 18 % at both 18 months and 24 months bottle age compared to the control wines. The addition of lees recovered from the primary fermentation to Chardonnay base wine depleted total protein concentration by 40 %, and by 50 % in Pinot noir base wine, from 18 months to 24 months bottle age. The b-glucanase enzymes treatment did not affect total protein concentrations in both Chardonnay or Pinot noir wines. Ageing on lees did not increase total polysaccharide concentrations in Chardonnay or Pinot noir sparkling wines, but the polysaccharides composition was influenced by the treatments. The ultrasound treatment facilitated the release of 10 % more total polysaccharide concentration in Pinot noir sparkling wines after 12 months ageing, attributed to yeast breakdown. The microwave treatment decreased total polysaccharide concentration by 15 % in Pinot noir sparkling wines after 24 months ageing. Addition of lees to Chardonnay or Pinot noir base wines enriched total polysaccharide concentration by 20 % after 18 months bottle age. Total polysaccharide concentrations in the wines appeared not to be influenced by wine storage temperature (15 °C or 25 °C). Foam properties were influenced by grape variety, yeast treatments and bottle age. The decrease in total protein concentration in sparkling wine was associated with foam volume variation and increasing foam velocity with increasing time on lees. Foam stability was unchanged irrespective of wine storage temperature (15 °C or 25 °C). The sparkling wines had similar foaming properties, except for the high temperature storage treated wines and ultrasound treated wines in both Chardonnay and Pinot noir varieties. High temperature storage effected the lowest total protein concentration in the wines compared to the rest of the wines, and an associated decrease in average foam lifetime that was related to an increase in foam velocity. The effects of ultrasound treatment resulted in elevated average foam lifetime in Chardonnay wines and elevated foam velocity in Pinot noir wines at 18 months bottle age. This study offered a rapid approach to visualise alterations to yeast morphology and revealed important changes that occur especially when autolysis was accelerated. The work enabled the categorisation and quantification of yeast morphologies associated with the ageing of sparkling wine, providing a better understanding of the mechanisms of yeast lysis in traditional method sparkling wine production. The influence of yeast treatments on wine composition, and effects on sparkling wine foaming provided a better understanding of the interactions of impact compounds affecting foaming properties. Further exploration of microwave, ultrasound or addition of b-glucanase enzymes treatments of yeast is warranted as tools towards accelerated autolysis for elevated concentrations of desirable compounds released into wine, and the optimisation of production processes to improve sparkling wine quality.