A Summary of Wine Corks

I think everyone has been forced to write down their 'future dream job' when they were in the lower grades of elementary school. Not really understanding the definition of a 'job,' I wrote 'Jackie Chan' while my friends around me were writing 'astronaut' or 'doctor.' That paper was collected and posted in the hallway for all classes to see. As a child, I was feeling that 'Kaiji: Ultimate Survivor' sense of dread, but then a miraculous answer appeared: 'airport conveyor belt,' which saved my life. In short, you never know what will happen until the very last second, so I hope those currently taking the sommelier primary exam will keep doing their best without giving up.

Anyway, the other day I posted a simple summary of wine stoppers on Instagram, and it went viral. It felt like everyone was just waiting to see corks—you should have told me sooner! This project is meant to capitalize on that post. I will thoroughly explain wine stoppers.

1. Natural Cork

Natural cork is a renewable natural material made from the bark of cork oak trees. It is lightweight and elastic, and the act of 'popping the cork' is accepted as part of the enjoyment of wine. Short, low-quality corks are used for early-drinking wines, while high-quality, long corks are used for premium wines intended for long-term aging—definitely something to remember. On the other hand, the biggest drawback is, as you know, the

risk of cork taint (TCA: trichloroanisole)—a defect that produces an off-odor like mold or wet cardboard, estimated to affect about 3–5% of all bottles. I haven't encountered it myself yet, but apparently, it's a stench you can identify instantly. Furthermore, because it is a natural material, it is also worth noting that

oxygen transmission rates vary from cork to cork. As a result, when stored for a long period, bottle variation can occur, where the aging process differs even within the same lot of wine.

2. Technical Cork

Technical cork is a processed cork developed to improve upon the cost and TCA risk weaknesses of natural cork. The following three types are representative.

① Agglomerated Cork
The cork at the top of the photo, made by binding cork particles with adhesive. It is inexpensive but has low durability and is intended for early-drinking wines.

② 1+1 (One-plus-one) Cork
The cork in the middle of the photo, featuring a structure with agglomerated cork in the center and natural cork discs attached to both ends. This type aims for a balance between cost and quality.

③ Diam Cork
The cork at the bottom of the photo, the familiar DIAM. It is a closure reconstructed after washing cork particles to remove TCA. Its greatest feature is that the oxygen transmission rate can be precisely controlled according to the intended use. It maintains a usage experience close to that of natural cork while significantly reducing quality variation.

3. Synthetic Closures

These are artificial corks made from food-grade plastic. They are the most difficult to remove and are corks whose purpose is sometimes unclear.

① Moulded Type
Relatively hard and difficult to reinsert into the bottle. Also, because their oxygen barrier properties are low, they are suitable for wines meant to be consumed within a few months.

② Extruded Type
Highly elastic, and products with various oxygen transmission rates are sold. Brands like Nomacorc are designed to handle long-term aging. A drawback is 'flavor scalping,' where the plastic absorbs aromatic compounds from the wine.flavor scalping

4. Screwcap

Currently one of the most widespread closures. Because an aluminum cap is screwed onto a specialized bottle to seal it, no corkscrew is needed to open it, and TCA contamination does not occur is its greatest advantage. In Australia, New Zealand, and the UK, they are widely adopted even for premium wines. On the other hand, in some markets like the US and China, the image of it being a 'cheap wine stopper' still remains. There are mainly two types of liners inside the cap:

① Tin Liner:
almost completely blocks oxygen. However, because oxygen supply is extremely low with a Tin liner, reduction in the bottle can occur, leading to unpleasant odors like onion or sulfur. Therefore, winemakers must carefully adjust the amount of SO₂ added during bottling.

② Saran Liner:
Unlike the Tin liner, this allows a small amount of oxygen to permeate.

5. Glass Stopper

Finally, the glass stopper. A representative brand known is Vinolok. It is a method of sealing by combining a glass stopper with a resin ring, and it has storage performance comparable to natural cork. On the other hand, a specialized bottle is required to ensure airtightness. Also, the price is very high, comparable to the highest-grade natural cork, so it is mainly adopted for premium and super-premium wines.

That covers the five basic types.