What is wine cork and how it affect wine quality?

  • Friday, Day 11/06/2021
  • wewine-kien-thuc-ruou-vang-nut-ban-la-gi-wine-cork-knowledge

     

    How much do you know about the small piece of cork that keeps the precious drink from spilling or spoiling? It is made from the bark of oak trees, often grown in Spain, Portugal,... Besides, in the production process wineries only use the bark and minimize the damage to the inner part of the tree.

    To learn more about the cork, first, let's go back in history to understand their origins:

     

    1. History of the cork:

    In 1,500 BC, archaeological records show that, in the period of ancient Greece, the Phonecians knew how to use cork for terracotta pots used for wine (now called as it is today. under the name Amphora), cork gradually replaced most of the earlier primitive materials such as cloth, earth, and leather.

    But in the Middle Ages, winemakers switched to using wooden barrels to store wine and since then cork has fallen out of favor and gradually forgotten.

    It wasn't until the early 17th century that people created wine bottles made of glass, replacing wooden barrels, and Amphora vases. At first, the craftsman made glass corks, but problems quickly arose, when the cost was very expensive, plus the processing technique was not sophisticated, leading to frequent breakage of wine bottles when opening and closing the cap. For the same reasons, cork is once again favored and reused. To this day, the cork still plays the role of a loyal partner in wine.

    Bình rượu vang thuỷ tinh ở thời kỳ đầu
    Glass wine bottles in the early days (Source Internet)

     

    2. Cork production process:

    To produce cork, craftsmen had to go through 3 main stages:

    First: Harvest the bark of the oak tree

    The cork is made from the bark of the oak tree (also known as Quercus Suber).

    From May to the end of August, farmers begin to select oak trees that are at least 25 years old. The peeling must be done very gently to avoid injury to the inner part of the tree. Harvesting on each oak tree only takes place every 9-12 years, to give the oak tree enough time to regenerate new bark.

    Thu hoạch vỏ cây sồi
    Cork production process (Source Internet)

     

    Step 2: Clean and disinfect

    Before shaping the cork, the worker will put the pieces of bark in a steel barrel containing boiling water, and a fungicide solution. Thanks to this sterilization stage, the barks will be softer and easier to shape the button in the next step. At the end of this process, workers will select unsatisfactory barks, crush them, and create another type of cork at a lower cost.

    Làm sạch và khử khuẩn
    Clean and disinfect (Source Internet)

     

    Step 3: Create a shape for the cork

    At this final stage, the craftsman handcrafts a large piece of bark into the shape of a cork, and the finished product is called "Natural Cork". Before putting it on the market, the manufacturer must sterilize the cork again, and put it into the machine to classify them correctly.

    Prices may vary depending on the quality of the cork.

    Tạo hình cho nút bần
    Create a shape for the cork (Source Internet)
    Nút bần sau tạo hình
    Create a shape for the cork (Source Internet)

     

     

     

    3. How does cork affect wine quality?

    Advantages:

    - When the researchers did a test, they found that more than 80% inside of the cork is air and it has the structure of alveoli (like a honeycomb), so it has very good elasticity and compressibility, plus impermeability. All of these factors help the cork stretch to seal the mouth of the bottle, preventing alcohol from escaping.

    - Each year, wine bottles intake 1 milligram of oxygen through the natural cork. At first glance, this seems like a pretty small amount, but what do you think after two or five years? The amount of air that accumulates is enough to break down the SO2 that winemakers have added to reduce oxidation. But this amount of air is great for aging wines, as they help the wine matures in the bottle, develop flavor and structure, and help soften the tannins.

    Weakness:

    - Natural cork is susceptible to the smell of cork (also known as Cork Taint) - Cork taint is formed by the compound 2,4,6 - trichloroanisole (TCA). This chemical compound affects most wood-based materials, so they are cork's worst enemies. The cause is thought to be due to: the chlorine solution used in the sterilization process of cork comes in contact with some molds to form a different form of the compound. When the cork is contaminated with this compound, the wine will take on an unpleasant aroma such as damp cardboard. According to research estimates, TCA affects 1-5% of world wine production.

    Depending on the quality and brand, one cork can cost three times as much as the other, which increases the final selling price of the wine.

     

    4. Classification of cork:

    In addition to natural cork, and to meet many different needs in terms of cost, as well as different wine properties, of customers. Manufacturers have created different types of buttons as follows:

    Technical Stopper/ Twin Top Agglomerated Stopper

    This type of button is made from pieces of wood leftover from the production of natural buttons, then crushed and glued together with a special glue mixture. The two ends of the button are glued with 2 pieces of intact natural wood, so it inherits the advantages of natural cork, but the price is cheaper.

    Nút bần kỹ thuật technical stopper
    Technical Stopper/ Twin Top Agglomerated Stopper (Source Internet)

     

    Agglomerated Stopper

    This line of buttons is cheap, often used for wines with a shelf life of 2 to 3 years. The composition is similar to the technical cork, but the only difference is that the two ends of the cork are not added with natural wood pieces, so their effect on the wine is also less.

    Nút ép ( Agglomerated Stopper)
    Agglomerated Stopper (Source Internet)

     

    Champagne Stopper

    Due to the specific nature of sparkling wine, the production of cork is also different. As you all know, the pressure of a bottle of sparkling wine falls to 5-6 bars ATM, along with a large amount of CO2 in the bottle, so to ensure safety during storage and transportation, cork is required. Zinc ring surrounds to hold the stopper along with the bottle. Due to the presence of CO2 in the bottle, it is necessary to use a natural wooden stopper to reduce the possibility of gas escaping, but the natural wooden cork is too soft, so opening the bottle of sparkling wine becomes difficult. so it is safer and easier, one needs to combine it with the above-engineered wood button.

    Before the wooden cork is sealed into the bottle, its shape is straight and measures 31 mm, after pressing into the bottle, the stopper part is reduced to 18 mm to fit the bottle mouth, this creates the funny shape of the cork. . The lower body then expands and blocks when CO2 escapes to the outside.

    Upper part: Agglomerated Stopper

    Water-alcohol contact part: Extra adhesive 1,2, and 3 intact pieces from Natural Cork, about 6mm thick.

    Nút Sâm Panh (Champagne stopper)
    Champagne stopper (Source Internet)

     

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    References:

    • https://tanglewoodwine.co.uk/blogs/news/how-wine-corks-made
    • https://www.fix.com/blog/alternative-wine-closures
    • https://www.winemag.com/2019/04/23/wine-closures-pros-cons
    • https://winefolly.com/deep-dive/chemist-explains-corks-matter-storing-wine