Source: http://r4nt.com/images/2008/12/wine5_lg.jpg

The start of a new year calls for a discussion about none other than sparkling wine!  Cheers and Happy New Year to you!

The precise origin of sparkling wine remains an active discussion; however it was known that wine containing bubbles was originally thought to be a wine fault during the Middle Ages. The source of the bubbles was poorly understood during this time, and as early as Ancient Greek and Roman periods.  Dom Pérignon, who is known to be the “father of Champagne”, actually spent his time trying to prevent bubbles in the wine from occurring, as a result of a few too many bottles exploding in the cellar from the pressure.  It was the British, who were the first to see bubbles in wine as a positive trait, that presented one of the first scientific papers on what they believed the mechanisms behind the bubble production was, and who were the first to attribute the process of adding sugar to a wine before bottling to the creation of bubbles.

Since the days of misunderstanding and eventual mechanism discovery in the 1600s, several different methods for producing sparkling wine have been established: the traditional method (a.k.a. methodé champenoise or champagne method), the charmat method (a.k.a. Metodo Charmat-Martinotti, Metodo Italiano, bulk method, tank method, or cuve close), the transfer method, and gas injection.  While the traditional method is the most widely known and used, other methods have proven to be not only acceptable alternatives (for the most part), but also much faster and less expensive than the traditional ways.

All sparkling wines undergo a secondary fermentation, by which sugar and yeast is added to a still base wine, resulting in the production of carbon dioxide gas.  The location of this secondary fermentation is typically what distinguishes different production methods from one another.  Briefly, with the traditional method, secondary fermentation occurs within the bottle.  The wine is then left to sit for at least a year and a half on its lees, maturing and obtaining characteristic aromas and flavors.  After this lengthy aging time, the bottles are riddled, which requires slight daily turns until the bottles move from horizontal to inverted vertical.  The neck of the bottle is then frozen, isolating the small cap of lees and other sediment (a.k.a. “bidule”).  The bottle is then disgorged by uncorking the cap and letting the pressure behind the bidule to quickly expel it from the bottle.  Since some of the liquid is lost during this process, the bottle is topped off with dosage, a mixture of wine, sugar, and other ingredients to complete the final sparkling wine.

For the charmat method, secondary fermentation occurs in stainless steel tanks and is subsequently bottled under pressure.  The cost of this method is often much less than the traditional method, and it allows the winemaker to produce more sparkling wine in a faster period of time than the lengthier traditional method.  The taste of charmat method sparkling wines tends to be fruitier in character than the traditional method sparkling wines that tend to possess more toastiness, yeastiness, and nuttiness.

In the transfer method, the first stages of secondary fermentation are similar to that of the traditional method in that secondary fermentation occurs in the bottle.  Once secondary fermentation is complete and the wines have been aged on their lees for a period of time, the individual bottles are then combined into a larger tank.  In the tank is where the dosage is added, and then the wines are rebottled.  According to users of the transfer method, by adding the extra step of combining and rebottling, an extra level of complexity is added to the final wine.

In addition to these advances or alternatives in methods for creating carbon dioxide bubbles in sparkling wine, there have been many other biotechnological advances in the fermentation step of sparkling wine making.  In particular, some of these advances have played (and are playing) important roles in improving the quality of the wine, including selection of specific yeasts, immobilizing yeasts, and enzymatic treatments.  Even as physical winemaking technologies evolve over time, changes in biotechnologies will become increasingly important; in order to further improve sparkling wine making quality.

Selection of Yeasts

Saccharomyces cerevisae, otherwise known as the “wine yeast”, has been thoroughly studied for a great number of years.  During sparkling wine fermentation, slower rates of fermentation are preferred, as it promotes better foam and a nice bouquet.  If the conditions for fermentation are not ideal for a slower rate, having a good base wine, a good selection of yeast strain, and controlled temperature conditions can lead to improved secondary fermentation.   Selection of a yeast strain with high flocculation capacity (lumping; which helps remove it from the final wine at disgorgement) improves the ability to remove the bidule at disgorgement, and thereby increases the overall quality of the wine.

Studies have shown that hybrid yeasts, formed by S. cerevisae and S. bayanus var. uvarum, increases the flocculation capacity and has the ability to perform well in fermentations at both high and low temperatures.  Future research examining genetic modification of yeasts to produce higher flocculating strains may provide further improvements in the quality of fermentation in sparkling wine.

Another source of improvement in the selection of yeasts in sparkling wine fermentation is selecting for autolytic strains.  During contact with the lees, yeasts undergo autolysis, which releases compounds into the wine which influence wine quality and sensory characteristics.  Studies have found that deletion of specific genes or UV mutagenesis of yeasts result in increased autolysis, which results in an overall increase in the quality of the finished wine.  Specifically, mannoproteins are among the most important compounds released during autolysis that contribute to wine quality, thereby selection of yeast strains that show increased levels of mannoproteins would be beneficial for increasing sparkling wine quality.

Immobilized Yeasts

Immobilized yeasts  have recently been studied as biotechnological improvements in the riddling and disgorgement steps of sparkling wine production.  Yeast immobilization works by attaching yeasts to beads (e.g. k-carrageenine or sodium alginate beads, polysaccharide gels, etc) and immersing the complex into the base wine at the beginning of fermentation.  As the yeast cells grow, they remain trapped in the beads, resulting in improved wine clarity.  Even while bound with the bead complex, the yeasts are still able to interact with the wine to produce similar quality and sensory characteristics as a wine made with free floating yeasts.

The technological improvement is most noticed during the riddling and disgorgement process, as the heavier weight of the yeast/bead complex allows the complex to settle almost immediately upon inversion of the bottle, significantly decreasing the length of time typically required during this stage.  Studies have shown that by using these immobilized yeasts, production time is not only decreased, but the finished wine is completely free of cells and sensory quality is maintained compared to wines made in the traditional method.

Future Research and Conclusions

Even though there have been many studies on autolysis in yeasts and the effects on wine quality improvement, the results of which could be written up in another whole blog posts and therefore I’ll skip over the details for today; there are still many questions that need to be answered.  Processes that are still unknown is the mechanism for the induction of yeast autolysis during the aging of wine; the kinetics of glucanase activity (which improve the release of mannoproteins, which have been linked to improved sparkling wine quality); and the mechanism for the release of nucleotides, nucleosides, and lipids.  Some studies have found that there is a relationship between the lipids released during autolysis and foam quality in sparkling wine, however, the mechanism behind this is also unknown.

It is important for research to continue examining the mechanisms behind autolysis, yeast strain selection, immobilization of yeasts, and other biotechnologies not discussed today, since advances in this field may provide important technologies for improving the quality of sparkling wines.  Combining chemical analysis with sensory analysis of wines enhanced by biotechnology will likely improve the quality of sparkling wines across the globe.

About The Author
Rebecca Yeamans

Becca Yeamans is the owner/writer of the science-based wine blog, The Academic Wino, as well as the Tasting Room Manager at a vineyard in central Virginia. With a Bachelor of Science in Biology and a Master of Science in Environmental Science, her solid background in science and research allows her to approach wine blogging with a unique style that is both informative to those in the industry, and entertaining for those simply wishing to learn.

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