The Yeastie Boys


To begin this month’s wine article, I have just one thing to say:

C6H12O6   →   2C2H5OH   +   2CO2.

No, fear not I have not gone all Einstein on you with the wine column. I have decided to focus on a single (albeit, probably the most important) process in the production of wine. The above equation is the scientific reaction of glucose and fructose (the sugars) being converted into ethanol and the by-product of this reaction, Carbon Dioxide.

Many ‘right on’ (fist punch in the air!) winemakers like to say that their ‘wine is made in the vineyard’, and yes, they would be right. However, it is once the grapes are brought into the winery, crushed and then with the addition of either wild or cultured yeasts that the real magic begins to happen.

“Only somebody who really takes the time to understand Pinot’s potential can then coax it into its fullest expression. Then, I mean, oh its flavours, they’re just the most haunting and brilliant and thrilling and subtle and… ancient on the planet.” Miles Raymond, from the film ‘Sideways’.

When I visited the charming biodynamic and Demeter certified Klus177 winery in November (located in Aesch, just 14Km away from Basel). Fermentation of their Muller-Thurgau, Pinot Gris and Pinot Noir was well under way. By the time that you read this the fermentation of their white wines will have been completed whilst the Pinot Noir may still be fermenting for about another 2 -3 weeks.

White wines are fermented without their skins, whilst red wines are typically fermented with their skins and stems in contact with their juice.

The grapes that are to be harvested from the vineyard will be at their optimum sugar levels and the plots in the vineyard will have been selected for picking that day by the winemaker and vineyard manager. They will have decided what part of the vineyard the grapes are to be picked depending upon grape type. These picking times and dates will differ between Chardonnay, Riesling, Pinot Noir etc as their sugar picking levels are all different depending upon what type of wine they are wishing to produce from their vineyards. The more sugar present in the grape the higher the amount of potential alcohol in the resultant wine.

“Wine is the only artwork you can drink” – Luis Fernando Olaverri. 

Centuries ago, winemakers then did not realise the effect that yeast has upon the grape and the resultant wine. They had no conception as to what yeast was or even how numerous the different strains there were. This tiny organism is the essential ingredient in achieving a great wine from good grapes. When a winemaker selects his yeast, he/she is in effect choosing the destiny of the wine they are about to make.

Fermentation is begun by putting the grape juice into a container, at the right temperature, then adding yeast. Fermentation is kick started with the addition of the chosen yeast that the winemaker has selected to make their wine with. This yeast then catalyses a series of reactions that then precipitates in the conversion of sugar into ethanol. The driving force of this reaction is the release of energy that is stored in the sugars that then results in this biological process. This is all carried out under a covering blanket of CO2 which is present in order to prevent the nasty oxygen from reacting with the wine discolouring the juice and making it taste off. In some cases, especially with Riesling the fermentation process will be stopped early in order to leave some residual sugars and sweetness.

Halting the fermentation process can be achieved by dropping the temperature thereby making the yeast inactive and sterile. The winemaker will then filter the wine in order to remove the dead yeast particles from the precious juice.

To look at fermentation from the perspective of the yeast. The sugar in the wine is merely a plentiful source of food. Through the process of eating this sucrose enriched juice they pump out alcohol and carbon dioxide as a by-product.

The selection of yeasts is varied and numerous. If you wish to produce a Syrah with the characteristics of smoke, tannin, ripe red fruits and deep liquorice notes then the yeast you require is Lalvin ICV-D80. If you desire a Riesling (like I do right now!) then the yeast strain that will give you those flavours of apple, pear, refreshing acidity and floral notes, well the Steinberg-Giesenheim yeast is the one for you. I could go on and detail the other yeasts that will encourage fresh citrus notes (W-15) or R-HST that will release flavours of peach, rose and a delightful minerality but that would all be quite boring.

Miles Raymond: Mmm…a little citrus..maybe some strawberry..(smacks lips). Passion fruit?….and Oh, there’s just like the faintest soupcon of like asparagus and just a flutter of a, like a, nutty Edam cheese… from the film ‘Sideways’

There is another fermentation process that many wine producers like to put their wines through and that is the Malolactic fermentation process (also known as Malo or MLF). This is where the winemakers take that nasty old sharp Malolactic acid and convert it into the more stomach friendly creamy sensation that we can appreciate with many whites but most certainly with red wines. Malolactic acid is that tart, sharp acidity you will have experienced in say either a Granny Smith or Cooking apple. Lactic acid on the other hand is creamier and is to be found in yogurt, cheese and milk.

Chardonnay for example has a creamier taste than say a Sauvignon Blanc. This is the direct result of the Chardonnay undergoing malolactic fermentation and oak ageing. These buttery and oaky characters are the result of this process, however crisp whites such as Sauvignon Blanc, Riesling, Chasselas and Petit Arvigne do not receive any benefit from the Malo process. Here the Malolactic process is stalled through chilling the wine and filtering it. Although in some cases for example in Chablis, the producers will ferment their Chardonnay in stainless steel using temperature-controlled tanks to keep the wine light, sharp and fruity.

Malolactic fermentation is a bit of an odd one though as it doesn’t require any yeast and solely relies upon an enzyme called Oenococcus oeni to eat the Malic compounds which it then converts into the softer more mouth friendly Lactic acid.

This reduction in the acidity of wine was first identified by the Swiss Enologist Hermann Müller in 1891 who theorised that this bacterial enzyme was responsible in the degradation of acid in wine. In 1882 Hermann Müller along with a team of other vineous minded boffins created the delightful Müller-Thurgau grape (incorporating the name of the village in which he was born). It was this grape being fermented that I saw a few months ago, back at the Klus177 winery in November undergoing the fermentation process. I shall return soon to purchase a few bottles of this elixir and raise a glass to Hermann and the work that he pioneered here in Switzerland.

“A bottle of wine contains more philosophy than all the books in the world” –

Louis Pasteur.

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