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“Corks are natural and technological objects”

In addition to producing good sparkling wine, you also need a good cork, which, when you think about it, is a real challenge. The company Sibel-Oller based in Reims since 1892 is one of the leaders in this sector and is quite rightly taking an increasing interest in the Luxembourgian market.

There is no love lost on corks. They are generally only ever mentioned in critical terms for spoiling a wine. If they have done their job well, nothing is said. Corks are forgotten as quickly as they are popped. This dismissive treatment is somewhat unfair considering the service they provide. Indeed, as Alexandre Marcoult, CEO of Sibel-Oller, one of the market’s biggest cork producers, quite rightly points out, “corks are natural and technological objects.”

Nowadays, a wide variety of corks are available. In addition to those actually made of cork, you can also get agglomerated, plastic, glass and porcelain stoppers, as well as screw caps. However, for sparkling wines whose second fermentation takes place in the bottle (champagnes and crémants) only a natural cork will do. This consists of an agglomerated body (bonded cork granules) topped by one to three cork discs. “These wines need physical properties inherent to cork,” explains Alexandre Marcoult. “Cork is the only material that is liquid-tight yet permeable to gas, which is essential for ensuring that the wine continues to develop in the bottle.”

Unlike still wines, virtually no single-piece cork stoppers exist for sparkling wines due to the pressure inside the bottle, which is between 6 and 8 bars depending on the storage temperature (the warmer it is, the higher the pressure). “The grain must be horizontal to ensure that the cork is leak-tight,” he explains. “A vertical grain could channel the pressurised liquid out of the bottle.” Very thick sheets of top-quality cork would be needed to produce 48mm-long corks (the length required for sparkling wines) and these would be “virtually impossible to find”.

“Cork is first harvested 40 years after planting. However, the sheets initially extracted are not appropriate for manufacturing corks.”

Screw caps for sparkling wines are available from Australia. Their major advantage lies in offering a convenient means of recapping bottles. However, they also prevent the wine from breathing. They are therefore used for lower quality sparkling wines and are completely inappropriate for champagnes and crémants. Cork still has a bright future.

Geographically speaking, it is remarkable in that it only grows in the Mediterranean region. “Eighty percent of global production takes place in Spain and Portugal,” notes Maxence Burlot, sales director of Sibel-Oller. “The remaining 20% is produced in Sardinia, Corsica and North Africa.” The company from the Champagne region has a solid presence in Spain with two production sites in Catalonia and Estremadura, “near forests where the oak trees grow”.

Sibel-Oller has none of its own plantations and instead buys quercus suber (the Latin name for the cork oak) bark from over 65 suppliers, many of whom have had contracts with them for several generations. Trust is essential when the quality of a material is so essential and takes such a long time to emerge. “Cork is first harvested 40 years after planting. However, the sheets initially extracted are not appropriate for manufacturing corks. They have too many faults. So, we have to wait 9 to 12 years, depending on the climate, for the second harvest. This cycle continues until the tree is 200 years old.“

In 2015, Sibel-Oller invested €700,000 in its Reims factory. Here, it produces high-end corks for the most prestigious champagne brands, including Roederer, Bollinger, Deutz, Taittinger, and Selosse. The company produces 290 million corks a year.

“The quality of crémants genuinely surprised me“

It is very proud of its Living Heritage Enterprise certification “which ranks us alongside the top luxury companies and is a tribute to our employees’ know-how, which often cannot be learnt at school.”  Another positive factor is that the cork maker is the only company able to prove a negative carbon footprint of -27.6g of carbon per cork.

Since last year, Sibel-Oller has had its eye on the Grand Duchy where 3 million bottles of crémant are marketed each year. “Although our corks may not be the cheapest on the market, they offer the finest quality,” assures Maxence Burlot. They are the perfect match for increasingly high-end Luxembourgian crémants, whose quality genuinely surprised me.”

Domaines Vinsmoselle decided to trial the corks this year, joined by estates such as Laurent & Rita Kox. It must be a good sign if players from the Champagne region are taking an interest in Luxembourgian crémant!

From tree to bottle

Cork production is a long and complex process. It also comes with many closely guarded secrets. Here are the main steps.

 

Boiling: this helps flatten freshly harvested cork by softening it. The water is constantly tested to ensure it does not transmit any molecules causing a “cork taint”, in particular TCA.

Within three days, discs are cut from the sheets before any microbial activity can resume. Any waste is ground down and granulated to make agglomerated cork bodies.

Desorption: the discs are placed in a desorption chamber where they are subjected to cycles of hot air, damp air and cold air, which removes any compounds responsible for organoleptic deviations (which modify sensory perception). However, if desorption is too intense, the cork loses its mechanical properties.

Sorting: before being bonded to the end of agglomerated cork bodies, cork discs are sorted by laser into seven categories depending on their quality. They are then put through an x-ray machine (MRI), which detects any hidden defects in the core of the cork. Their moisture level is measured.

The cork bodies are all weighed individually to check their density. They are measured at several different locations. Then, their torsion resistance is tested.

Chromatograph test: corks are tested randomly using a chromatograph, which detects TCA levels. Sibel-Oller is the only cork producer to operate a chromatograph in the Champagne region. It has two more of them in Spain.

Manual sorting and sniffing: On exiting the chromatograph, the corks are conveyed on a belt where a further visual inspection is performed to ensure that nothing has been missed.

They may also be sniffed by a well-trained human nose, which is still more sensitive than a machine. This is an option reserved for high-end corks. The task is performed by an employee whose predecessor trained her and who will train her successor.

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