labo Vinsmoselle 4

Harvest time for the men in white coats

His role in Domaines Vinsmoselle is crucial, particularly in the autumn. Despite this, Jörg Schmitt only ever sees the vines from afar through the windows of his workplace in Wellenstein. At harvest time, the laboratory manager’s work is examined meticulously by all the cooperative’s oenologists.

Domaines Vinsmoselle includes vineyards along the 42 km course of the River Moselle in the Grand Duchy of Luxembourg. Three cellars (in Wellenstein, Wormeldange and Grevenmacher) are required to accommodate wine-growers’ grapes during harvesting. The most southerly of these plays a special role, since the Wellenstein site not only houses the technical director’s offices, but also the cooperative’s laboratory, managed since 2014 by a young German, Jörg Schmitt (aged 33).

With its white-tiled lab benches, beakers, pipettes, vials filled with various solutions, mysterious devices connected to laptops, etc. the ambiance is a far cry from a subterranean cellar lined with stainless steel vats and oak barrels. Nevertheless, the main topic discussed here is still wine and grapes! And when he glances outside, Jörg Schmitt can still admire the Kurschels vineyard through the large windows.

Having graduated with a bachelor’s degree in food technology from Trier University, he had prior knowledge of the laboratory in Wellenstein as he attended his final-year placement here and wrote his dissertation about the experience. “Although it is only possible to specialise in wine later on in the programme, I have many friends in the sector and it was clear to me that I wanted to focus on this area,” he smiles.

At harvest time, his workload skyrockets as the information he provides is used by the cellar managers and the wine-growers’ committee for each centre receiving grapes to decide on a daily basis whether to harvest one parcel over another. “The grape and wine consultant Harald Beck visits the vineyards and takes samples, which I test,” he explains. “I test their sugar content and acidity levels and send the results to the relevant cellar manager. Using these data, they are able to predict the alcohol levels that musts (editor’s note: unfermented juice) are likely to reach and pick the best time for harvesting.”

In order to gain a good overview of how well the grapes are ripening, these tests must be performed weekly on test parcels. “During harvesting, I start work at 7 am and finish between 7 and 9 pm. During these four weeks, I perform up to 150 procedures a day including all the other tests such as must analyses.”

We can work faster and more flexibly with our own laboratory

In order to quantify the sugar levels in the grapes, Jörg Schmitt presses a grape to extract the juice and applies several droplets to the refractometer lens. By calculating the refraction of a light ray passing through the liquid, this device calculates the degrees Oechsle, and the sugar content is instantly displayed on the laptop next to it on the lab bench.

The process for determining acidity levels is slightly more complex. The laboratory manager pours some juice into a glass beaker, places a magnet inside it to allow it to mix effectively, and immerses a pH sensor in it. He then adds sodium hydroxide and fixes the container into a centrifuge. After this has operated for a good minute, the pH level is displayed on the screen.

The data displayed for this year’s grapes are generally exciting: “We have seen a good degree of ripeness combined with slightly higher acidity than last year, which is very good for the wine,” says Jörg Schmitt.

At harvest time, he is also responsible for microbiological testing of musts and consequently for the sterility of the presses, which are cleaned every evening. The musts and machines are tested using materials that react to the presence of bacteria. For example, a pink gel contained in small transparent plastic boxes is used to check that the press is sterile. “What we really want to avoid are the yeasts that grow naturally on clusters of grapes on the vines but must be eliminated during wine-making,” explains Jörg Schmitt. Although they are not bad per se, they can sometimes be uncontrollable.”  Consequently, presses are inspected twice a week during harvesting.

But why do the Domaines Vinsmoselle need a laboratory at all when the Wine Institute lab in Remich offers its services to producers at very low rates? “We work on over half of all the vines in Luxembourg, which amounts to a very large number of parcels and different vintages. We can work faster and more flexibly with our own laboratory. Sometimes, the cellar managers come to us with special requests, and if these are urgent, we can provide results within a very short space of time.” The quality of information is essential in situations where decisions must sometimes be taken very quickly. And the laboratory is where it all happens.

Wines are tested too

Please don’t think that the Domaines Vinsmoselle laboratory is open just one month per year! The cooperative checks each vintage when it is bottled and later when it is placed on the market, “not just to ensure that each wine is safe, but also that it meets quality standards in terms of flavours and aromas so that each vintage satisfies consumers.”

Crémants undergo a special procedure during testing to ensure that there are no remaining traces of carbon dioxide, the gas used to produce the bubbles. They are passed through a filter before being poured into a beaker and stirred with a pipette to eliminate any remaining bubbles.

Wines are bottled throughout the year: “It all depends on fermentation and maturation times as well as our customers’ requirements.  There is no downtime. Even during harvesting, wine and crémants are bottled and everything always has to be perfect!”


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