Novel Methods to Manipulate Autolysis in Sparkling Wine: Effects on Yeast

Abstract

Sparkling wine made by the traditional method (Méthode Traditionelle) develops a distinct and desirable flavour and aroma profile attributed to proteolytic processes during prolonged ageing on lees. Microwave, ultrasound and addition of β-glucanase enzymes were applied to accelerate the disruption of Saccharomyces cerevisiae, and added to the tirage solution for secondary fermentation in traditional sparkling winemaking. Scanning electron microscopy and flow cytometry analyses were used to observe and describe yeast whole-cell anatomy, and cell integrity and structure via propidium iodide (PI) permeability after 6-, 12- and 18-months post-tirage. Treatments applied produced features on lees 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 was used to discriminate yeast populations; features consistent with cell disruption were observed in the microwave, ultrasound and enzyme treatments, as evidenced by up to 4-fold increase in PI signal in the microwave treatment. Forward and side scatter signals reflected changes in size and structure of yeast cells, in all treatments applied. When flow cytometry was interpreted alongside the scanning electron microscopy images, bimodal populations of yeast cells with low and high PI intensities were revealed 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. This work offers both a rapid approach to visualise alterations to yeast cell surfaces and a better understanding of the mechanisms of yeast lysis. Microwave, ultrasound or β-glucanase enzymes are tools that could potentially initiate the release of yeast cell compounds into wine. Further investigation into the impact of such treatments on the flavour and aroma profiles of the wines through sensory evaluation is warranted.

Towards Accelerated Autolysis? Dynamics of Phenolics, Proteins, Amino Acids and Lipids in Response to Novel Treatments and during Ageing of Sparkling Wine

“…These differences were not evident until 18 months of bottle storage and reflect both decreases in proline concentration in control and ultrasound treated wines and increases in microwave and enzyme-treated wines relative to their respective concentrations at six months. This was possibly related to treatment-induced stress on the yeast that triggered cell degradation [4,9] and autolysis associated with longterm cellular degradation previously reported by Gnoinski et al [50] who found that yeast cell walls were permeable to propidium iodide ingress following microwave, ultrasound, and enzyme treatments. Similar to reports by Moreno-Arribas et al [16], proline was the predominant amino acid in the wines.…”

“…We attribute this to hydrolytic activity that led to the degradation of yeast cell walls making membranes more susceptible to degradation. Prior work in our laboratory reported observations of increased numbers of cavitated yeast cells in response to the ultrasound and β-glucanase enzyme treatments relative to the control at tirage [50].…”

“…To explore the effects of treatments on the wine matrix, yeast cultures (2 × 10 6 cells mL −1 ) were prepared from S. cerevisiae IOC 18-2007 (Institut Oenologique de Champagne, Lallemand, Adelaide, Australia) [51] and subjected to microwave or ultrasound or β-glucanase enzyme treatments according to the methodology described by Gnoinski et al [50], as follows: (i) A household microwave oven (Panasonic 'the Genius' Shanghai, China, 1100 W, 50 Hz, 100% power) was used to heat 1.0 L yeast culture in a Schott bottle up to 99 • C, (ii) An ultrasonic bath (Soniclean 2000TD Ultrasonic Bath, Thebarton, Australia) was operated at 50 kHz and 350 W to treat 1.0 L yeast culture in a closed Schott bottle over five cycles of 15 min each, with circulating cold water to maintain the bath water temperature between 20 • C to 25 • C, and (iii) For the enzyme treatment, 5 g L −1 β-glucanase enzyme (VinoTaste ® Pro, Novozymes, Winequip Pty Ltd.y, Victoria, Australia) was added to 1.0 L yeast culture in a Schott bottle, mixed well, closed and maintained at 20 • C for 24 h prior to use.…”

“…Liu et al [49] reported that microwave treatment of lees was less effective, possibly as the treatment time was not long enough, and moderate heating was also reported to promote polysaccharide release in a model wine system. Gnoinski et al [50] identified features consistent with cell wall disruption resulting from microwave, ultrasound or β-glucanase enzyme treatment of yeast at tirage.…”

Losses of Yeast-Fermented Carbon Dioxide during Prolonged Champagne Aging: Yes, the Bottle Size Does Matter!

“…It is indeed a common misconception especially when looking for the most prestigious cuvees. 15 During prolonged aging on lees, champagne and other sparkling wines develop distinct and desirable flavors and aroma profiles attributed to the proteolytic processes characteristic of yeast autolysis as recently described in minute details by Gnoinski et al 16 Yeast autolysis usually begins between two and four months after the second in-bottle fermentation. 17 Induced by a lack of nutrients combined with high levels of ethanol and dissolved CO 2 , low pH (∼3−3.5), and low temperature (12−14 °C) storage conditions, the irreversible degradation of several yeast cell-wall components occurs, such as glucans and mannoproteins for example.…”