Wine 2016 Jul 26 / Comments
After construction workers unearthed a bottle of old wine, a scientist discovered that its yeast lees were still intact. Markus Hungerbühler reports on what happened next.
The year 1895 was not only when Louis Pasteur – who discovered the principle of microbial fermentation – died, and H. G. Wells’s novel The Time Machine was published. It was also the year when an unknown winegrower produced a white wine in the village of Meilen on Lake Zurich in Switzerland. At that time, the Zurich area was the largest Swiss wine region, and the 1895 wine was made from a then-widely planted white grape variety, Räuschling.
This would have remained unremarkable, except that during construction work in Meilen in 2008, a bottle of this wine, along with one from the 1897 vintage, was found buried in sand, still sealed and intact.
Beauties revealed
Hermann Schwarzenbach, a well-known local wine producer, purchased the bottles and tasted them, as well as Räuschling wines from the 1911, 1927, 1935, 1936, 1940, 1943, 1945, 1947, 1959 and 1962 vintages, along with younger vintages up to 2007. Among the experts present at the tasting were Professor Dr Jürg Gafner, senior scientist in microbiology at Agroscope in Wädenswil, the Swiss Federal Centre of Excellence for Agricultural Research, located on the opposite shore of Lake Zurich. The wines were exceptionally fresh, unspoilt and, most interesting, unfiltered, a practice that only began around 1964.
The residue in the bottles caught Professor Dr Gafner’s attention. He says: “Surprisingly, close examination of the lees under the microscope revealed that the cells were still intact. This meant that the yeast was not dead but in a state of dormancy – a Sleeping Beauty yeast so to speak!” But how was this possible? Altogether six different strains of the Saccharomyces cerevisiae (S. cerevisiae) yeast were found, among other yeasts. One strain – the 1895C – of the three S. cerevisiae yeasts found in the 1895 bottle had developed particular mechanisms to survive. It nourished itself from the fructose after it had used all the glucose, making it a so-called fructophile yeast, like the strains 1895A, 1895B, 1935A, 1935B and 1962 as were later discovered. Professor Dr Gafner conducted fermentation experiments with strain 1895C. The results were again a great surprise and showed further astonishing properties. This strain starts the fermentation fast, produces little foam, and only very moderate amounts of sulphur compounds, volatile acidity and diacetyl, the last being responsible for the ‘dairy’ flavour in faulty wines. Additionally the quantity of lees after fermentation amounts to not more than one-third compared to all other commercially available yeast strains. Altogether, this yeast from 1895 promised excellent winemaking properties. But what about the flavours that this historic yeast produces in the wines?
Pure flavours
The 1895C strain of the yeast was reproduced on a small scale and offered to the winemaking community for the first time in 2011. There were further surprises. As a fructophile yeast, it successfully prevented and restarted stuck fermentations of grape musts. Such stuck fermentations occur when the glucose to fructose ratio falls below 0.1, that is, when there is 10 times more fructose than glucose.
Although this ratio may seem of little importance, research shows that almost 97% of stuck fermentations worldwide are caused by this low ratio. The fructophile character of the 1895C yeast is of particular importance, since commercially available dry yeasts have not, so far, been able to prevent and remedy stuck fermentations at this low ratio.
“This yeast offers the new possibility of preventing and remedying stuck fermentations without losing those very good properties that lead to high-quality wines,” says Professor Dr Gafner.
The yeast further allows for complete sugar consumption, producing bone-dry wines. And as for flavours, it preserves and enhances the varietal character, producing pure aromas which clearly express the grape variety in a manner unseen or, rather, untasted before.
Versatile use
After more wines were produced with this yeast, it turned out to be very versatile. It is not only suitable for producing still wines, but also traditional sparkling wines. Due to the small quantity of lees produced during the secondary fermentation in the bottle, the ejection of the lees from the bottle is easier and results in less spoilage of valuable wine. The yeast also makes for very pure fruit and grain mash destined for distillation, thus resulting in high quality spirits like Calvados and even Whisky.
Alive and kicking
Encouraged by these excellent results, the Swiss Wineyeast GmbH was founded in 2011. Production on a commercial scale started in 2013, employing the services of the biochemical company Lallemand.
Today, the yeast has been adopted by producers in France, Germany, Austria, South Africa, Switzerland and other countries. It is the first time ever that a dormant yeast found in very old wines has successfully been resuscitated and grown for commercial use again. Looking back today to the 2008 tasting and the old vintages of Räuschling, Professor Dr Gafner states, “I am proud of being the Prince who kissed Sleeping Beauty awake.”
And Louis Pasteur, had he been able to travel in a time machine, would have beeen amazed to see the far-reaching consequences of his discovery of microbial fermentation and what subsequent research has made of it today.
