Corks, the original kind, are made from the bark of the Cork Oak, which is harvested once every 20 years without endangering the trees’ life. For centuries they were simply punched-out cylinders of cleaned bark, but innovation has brought many kinds of manufactured corks, along with some made entirely without the intervention of trees.
Agglomerated wine corks are made from chipped cork pieces ground to a specific size and glued together with non-reactive polyurethane glue. Inexpensive and easy to handle, these are suitable for wines that will be held for short periods of time—less than a year.
Die-cut natural corks are punched out from cork bark. They rely on the density and elasticity of the natural cork bark to seal the wine bottle. They’re good for much longer periods. However, it’s all dependent on how much you’re willing to pay: the cheapest kind are not much better than agglomerated corks, but stepping up the price ladder means can expect your cork to last from 3 years to more than 10.
are made from food-grade, super high density, foamed polyethylene plastic with a food-grade neoprene coating. They are easy to insert and extract, do not chip, split, leak or rot, and are suitable for at least 5 years of aging, and in good cellaring conditions, over ten years, and require zero storage maintenance or pre-treatment.
The Long (and the Short) of It
How long should your cork be? Look realistically at how long you expect to store your wine before drinking, and figure out how much cork fits in your budget. A good rule of thumb is 'You get what you pay for.' The cheapest cork isn't always the best deal, and if you do decide to keep some bottles for the future, you may find yourself having to re-cork them in a few years.
Really cheap, long corks are not as good as more expensive, shorter corks. Quality is the most important factor, because as little as 2 millimeters of quality cork length will fully seal a bottle.
In addition, there is the problem of trichloranisole contamination. All tree-based corks can harbor a bad-smelling substance called trichloranisole. Industry statistics show that as much as 5% of all wine is spoiled by contact with contaminated corks—that is to say that even the costliest natural corks can spoil wine. This is why I strongly endorse Nomacorks, which never carry trichloranisole.
Preparing Your Corks
If you are using a small, hand-held corker (single or double-lever types) with natural corks you may need to prepare your corks by soaking them in warm water for 20 minutes. Whatever you do, NEVER SOAK YOUR CORKS IN SULFITE SOLUTION. Corks can soak up sulfite like a sponge, and when they go into the bottle they can release it (like a squeezed sponge) and dose your wine with an unknown amount of extra sulfite. Stick to plain water.
If you have trouble getting corks to pass through your hand-held corker even after soaking, you can try adding ¼ cup of glycerin to every gallon of warm water that you use for soaking. This ensures that the corks get enough moisture to lubricate their passage through the corker. However, this may cause them to crumble in the long term.
Some books talk about boiling corks or giving them a long soak in sulphite, but these are very bad ideas. Cork is tree bark, and boiling turns it to pulp. Long soaking does the same thing. Corks can soak up sulphite solutions and transfer them to the wine.
The trouble with handling corks that have sat in your cupboard for a while, or very dry corks is that it’s tough to judge how long you can soak them before they become mushy. However, there is a nifty trick you can use if you your corks are brittle either from age or low-humidity storage. You can make a cork humidor.
You will need a clean plastic bucket and lid, an empty wine bottle, and a 1.25% solution of metabisulfite, (that’s three tablespoons of sulfite powder dissolved in one gallon of cool water). Fill the wine bottle halfway with your solution, and carefully stand it up in the bottom of the bucket. Gently pour your corks into the bucket, filling the space around the bottle, supporting it and keeping it upright. Seal the lid on tightly.
Leave the bucket in a room-temperature area for about a week. In that time the liquid evaporating from the wine bottle will raise the humidity in the bucket to about 70%. This increases the humidity in the corks to 6%, making them pliant enough for easy insertion. The Sulphur dioxide gas coming off the liquid will prevent the growth of molds or spoilage organisms, keeping the corks sanitary. No further treatment of the corks will be necessary before bottling.
If you want to store your corks this way, replace the solution in the bottle every four weeks, and keep the lid tightly sealed. That way your corks will always be ready for use.
Nomacorks? Leave ‘em in the bag anywhere. They never dry out and don’t require pre-treatment in a floor corker. They may, however, be really hard to put in with a handheld or double-lever corker. Which brings us to...
There are several types of wine bottle corkers available. I cannot recommend enough using a floor corker. Other corkers (twin lever, single lever, and compression corkers) rely on human muscles to compress the cork and push it into the bottles. Floor corkers, while more expensive, use levers and mechanical advantage to carefully compress the corks and insert them precisely into the bottles. They also hold the bottles steady in a spring-loaded base. They are really worth the extra money.
After the corks have been inserted into the bottles it's a good idea to dry the top of the cork off with a clean cloth. This will prevent any moisture from forming mold there. While a spot of mold on the top of the cork wouldn't hurt your wine, it does look unpleasant.
You should leave your wine bottles standing upright for at least the first 24 hours after corking. The compressed air inside the bottle has to work its way out past the cork, and it can only do that if the bottle is standing up. If you immediately turn the bottle on its side, the pressure will still be there, but the wine will now be pushing against the cork, and could force it out of the bottle. After 24 hours (or two or three days: it isn't critical) you should turn the bottles on their side for long term storage.