On 15 February 2013, asteroid 2012 DA14 missed earth by a mere 27,700 kilometers. This ancient 130,000 ton asteroid, spanning 45 meters in diameter, would have released the same amount of energy as a detonating 2.5 megaton atomic bomb, had it collided with the earth. It looks like 15 February 2013 was global meteor day, as a 9 ton behemoth caused widespread panic and injuries as it seared through the sky above Chebarkul, a town in central Russia. Not really cataclysmic, these events, but certainly significant enough to put the thought of mass extinction into our minds.
Not only humans (and don’t forget the dinosaurs) are subject to mass extinction. Micro-organisms are intimately sensitive to changes in their environment. Take a tank of fermenting must. The savvy winemaker will manipulate this very complex environment to suit his and the fermenting yeast’s specific needs, but under certain conditions the yeast population can very quickly become extinct.
The eventual fate of the wine yeast is death. After churning out ethanol, flavour compounds and a myriad of other chemical compounds during its usually short life, the yeast unceremoniously dies. But still their job is not done. These dead cells (lees) also have a very important role, but for now the focus will be on some of the causes of death of fermenting wine yeasts.
Temperature, ethanol concentration, osmotic stress, pH, toxins, pressure, sulphur dioxide and volatile acidity can separately or in combination make your little buddies extinct. So best you follow this multi-part blog, as the next installments will focus on the specific factors listed above.
You might not be able to dodge projectiles from outer space, but you can do a lot to keep your little fermenting soldiers happy and alive right until the end.
Bernard Mocke is a technical consultant for Oenobrands
There is always a major lesson (or many) to be learnt in each harvest. A few years ago after planning space, bottling etc., I was convinced we had enough space at a cellar where I consult to take in the entire crop to spare. Little did I know the owner, with dreams of grandiosity, decided to buy in a few extra hundred tons. After three weeks the cellar was loaded to capacity and we were in full swing harvesting Sauvignon blanc.
For the first two days we could rack the SB. After that we could not even rack. Various options such as storage elsewhere and hiring tankers to stand for a day so we could rack in and out diminished to such a point that we were forced to ferment almost full tanks (1% headspace) on 100% lees.
Our cooling system was chilled water so the minimum temperature we could get was about 12°C. So I decided to inoculate at a rate of only 5 g/hl of Anchor VIN 13, as I knew this yeast gives very little foam. It is aggressive though, so my fear was excessive reductivity. I hoped to control this by keeping the fermentation temperature as low as possible (12°C), racking off the lees at about 5° Brix was also not an option at this stage.
I added 5 g/hl Anchorferm (inactivated yeast based nutrient), also at well below recommended dosage, so that I could avoid reductive characters. No ammonia was added at the early stages of fermentation. I took some comfort in the fact that the University of Bordeaux recommends high NTU content of about 200 NTU in SB for better formation of mercapto-pentanones, ours was over 400!
The fermentation kicked off at a phenomenal pace and after three days all tanks started H2S formation. I tried to ignore this until we had reached a residual of 7°Brix. At this stage I dosed with ammonia and started praying. (Funny how I always seem to pray when I am in total stress…)
Well, the H2S stopped within a few hours and most tanks finished dry without a recurrence. Copper man did not even have to make an appearance. Most tanks still had to lie on full lees for three to four weeks after dryness before we could get enough space in which to work.
Finally the resultant wines were assessed and my conclusion was that there were higher levels of tropical fruits in the lees fermented wines. Wines fermented with clear juice had higher ester levels. Our final blend was a combination of the two “styles” for our top label and the 100% lees wine for our second label. (Perhaps the wrong choice, as two years down the line the “lees” wine is showing better and better in the bottle!) No discernible bitterness on the “lees fermented” wines, they also show better mouth feel.
Lessons learnt when fermenting SB on full lees:
Keep yeast inoculation and nutrition at an early stage to a minimum.
Try and rack at 5-6°Brix.
Ferment with a good dose of Bentonite.
Keep the fermenting must cold (12- 13°C max).
Nitrogen addition as late as possible (but do remember nitrogen addition will have no effect if added too late).
The conclusion I came to was that it is possible to get a high quality wine when fermenting on full lees; however temperature control and various other factors must be controlled strictly. Above all remember no one knows everything. So, as said in the Hitchhikers guide to the galaxy, “Take along a towel and don’t panic.”
Mike Dobrovic is the former winemaker of well-known South African wine estate: Mulderbosch. He currently does some winemaking consulting, grows apples on his farm, writes poetry and dwells on all things spiritual.
“Don’t make a big monkey dance about choosing a yeast, just decide if you want esters or thiols!” This is one of the more memorable sentences that was uttered by Christoph Hammel during my recent harvest stint at his cellar in Germany. Before I put this sentence into context, I should mention that the Hammel Weingut has been in business since 1723. This proud winemaking tradition is continued by veteran and outspoken winemaker, Christoph Hammel. His skills include a combination of modern thinking, creative planning and solid experience based on many years of making wine with a scientific yet artistic touch.
Christoph is such a staunch believer in Anchor Wine Yeast, I guess that you could even call him an Anchorfile. He has repeatedly achieved success on a variety of grape varieties such as Grüner veltliner (fermented with Anchor Exotics and Anchor Alchemy I), Scheurebe (Anchor Alchemy II), Sauvignon blanc (Anchor Alchemy II), Dornfelder + Portugieser Rosé (Anchor Alchemy I and II), Müller-Thurgau (Anchor Alchemy I), Chardonnay + Weissburgunder (Anchor Alchemy I) and Sylvaner (Anchor VIN 2000), Riesling (Anchor VIN 13 and Anchor Exotics). Of special interest will be some the combinations of yeasts that Christoph likes to co-inoculate, such as VIN 13/NT 116 (also Anchor) and VIN 13/NT 116 together with Laffort X5. I have seen that these combinations have a massive effect on floral, fruity and tropical aromas, but no negative effect on fermentation kinetics.
Alex Halberstadt has the following to say about Sylvaner: “Nobody dreams about Sylvaner. Mentioning it in a group of wine people is akin to professing an interest in the finer points of cardboard fabrication. The grape bums people out.”
However, even a neutral grape variety such as Sylvaner stands to gain from these mixtures. For example, I inoculated Sylvaner with NT 116/VIN 7/X5 (as per Christoph’s instructions). Some of the tasting notes that I made over the course of the fermentation were: “tea leaf, fig, apple, floral, banana, grapefruit, spicy, curry, herbal, white pepper, grapefruit, and apricot”. In theory a more complex wine is possible because of the ester and thiol production of these yeasts and this is exactly what you’ll get in real life!
Something else that Christoph does, is oxygenation of the must and water mixture during yeast rehydration. In the photo below, you’ll see the white bin in which yeast is rehydrated and behind the bin you’ll see an oxygen tank.
Typically, the rehydration mixture is cooled down at 5ºC increments (with ample time intervals) until a temperature difference of approximately 5ºC is observed between the rehydration mixture and the must to be inoculated. Note that during all this, the rehydration mixture is continuously oxygenated by adding a steady trickle of oxygen. The rehydrated and happy yeast is then simply pumped to the tank in question. Christoph swears by this method and cannot remember the last time he suffered a stuck ferment. For more information on the science behind this, you are welcome to read my previous blog titled: “Is your yeast on sterols?”
More to follow…
Bernard Mocke is a technical consultant for Oenobrands.
The cooperative Vinicola de Villarobledo has been the only winery from La Mancha region to win a Gold award at wine contest – Nuevo Vino 2011 – held in Madrid on the 15th of June this year. This was the first time the cooperative winery presented a wine to this contest.
Martin Pardin (technical director of the cooperative) explains he wanted to innovate and create a very complex and unique red wine, adapted to modern demand for fruitiness, roundness and complexity in red wine. Grapes from Syrah, Tempranillo and Garnacha were partially destemmed, crushed and barrel fermented separately in 3rd fill French oak barrels. Martin used an extraction enzyme and a new yeast from Oenobrands, Anchor Exotics SPH, in all barrels. This yeast is an interspecies hybrid between Saccharomyces cerevisiae and Saccharomyces paradoxus. It is the only yeast of its kind worldwide. Fermentation took ten days at temperature range 18-27 °C, with four hand pigeage daily. For yeast nutrition, Biovin (bio-regulator of La Littorale) has been added after density of 1040. Martin was very happy with the results obtained with Anchor Exotics SPH as it satisfied his need to create a “highly fruity and complex red wine, different from a standard red wine of La Mancha region”.
Malolactic fermentation started spontaneously immediately after alcoholic fermentation and was completed within one month. The wines from the three varieties were blended and stored for five months. No fining was applied before bottling and Mannostab (Laffort) was added to secure tartrate stability.
Martin is very happy with the recognition this award gives to his winery and region, since all the other wines awarded came from other prestigious Spanish wine regions. He plans to increase production with his approach and will continue use of Anchor Exotics SPH as “a perfect tool to help him achieve complexity and fruitiness “. At the moment the wine is only available for sale in Spain but an extension of production in 2011 will allow the winery to have the wine available for export markets.
Patrice Pellerin is the technical manager for Oenobrands.