Home > Wine Storage Info > The Great Cork Debate: Natural vs. Synthetic vs. Screw Cap

The Great Cork Debate: Natural vs. Synthetic vs. Screw Cap

For the wine consumer, the Great Cork Debate is nothing if not confusing.  “Experts” sound off about the pros of one and cons of the other, often in complete contradiction with other “experts”.   It’s easy to find yourself bewildered to immobility in the middle of a wine shop, a natural corked wine in your left hand, a synthetic corked bottle in your right, and a screw cap in front of you.  Headaches like these can drive the most devoted wine enthusiast to consider collecting something else instead…perhaps hard liquor.

As it turns out, the loudest voices in support of synthetic corks and screw caps often belong to those who make their living bottling wine.  And this really isn’t surprising, considering that the wine stopper industry rakes in $4 billion a year, and that synthetic corks and screw caps are considerably cheaper to produce than traditional corks.

And they do have a strong argument for getting rid of traditional corks: cork taint.  Every wine collector has experienced that deep disappointment that comes when a bottle that’s been carefully aging for years opens up smelling like wet cardboard, due to a chemical compound called trichloroanisole (TCA), which occurs naturally in some corks.  Depending on which study you look at, cork taint affects between 3 and 15 percent of bottles.  Those aren’t numbers to be taken lightly, especially when we’re talking about the often-expensive wines meant for aging.

But what these proponents of man-made corks or screw caps usually fail to mention is that there are also significant problems with these cork substitutes.  Here are a few:

  • Synthetic corks don’t change with their surroundings. The glass that all wine bottles are made of expands and contracts with small temperature shifts in the environment around it.  Natural cork expands and contracts with the bottle, keeping the seal between wine and air consistently snug.  And environmental consistency is the number one rule of wine aging.  A too-loose synthetic cork can let in too much oxygen, ruining the wine by letting the alcohol turn into acetic acid, or vinegar.  A too-tight cork can be tough to remove from the bottle.  The latter is a common problem with synthetic corks: after about 18 months, they can be too tight to extract without a fight.
  • A small amount of oxygen is necessary for aging wine. Without oxygen, most of the natural reactions that occur between the hundreds of chemical compounds in a bottle of wine can’t happen, and the wine can’t develop so-called “aging flavors,” notes that can make a Chardonnay “buttery” or a Cab taste of truffles.  Screwcaps and synthetic corks prevent oxygen from getting to the wine.  Sure, this prevents over-oxidation, but so does drinking wine the day it’s bought.  In short, a synthetic-corked bottle doesn’t really “age”–it’s just taking up space in the cellar.
  • Screw caps can trap unsavory gases inside the bottle, ruining the wine’s aroma. Some of the reactions that occur within an aging wine result in sulfury gases.  These are allowed to dissapate through a natural cork and leave the wine, but are trapped by screw caps, resulting in a rotten-egg smell in the final product.
  • Synthetic corks and screw caps could leech chemicals into the wine. We don’t yet know how the compounds that make up plastics interact with the compounds in wine, but there are many studies that indicate the harmful effects the ingestion of plastics can have on the human body.
  • For once, it turns out that the old way of doing things was more environmentally friendly. Cork is taken from

    Recently harvested cork oaks

    cork trees in sheets once every ten years.  This process doesn’t harm the tree, and in fact, the cork grows back, making it a renewable resource.  A typical cork oak can continue producing for 200 years.  Cork orchards, with cover huge swaths of land in Span, Algeria, Morocco, Italy, Tunisia, France, and Portugal, provide an environment for flora and fauna, including endangered species like the Iberian lynx, Barbary deer, and the Imperial Iberian eagle.  Farming the cork provides jobs for over 100,000 people.  The cork trees also trap vast amounts of carbon dioxide, lessening pollution.  Almost 70% of the product from these cork farms goes directly to the wine stopper industry.  Without it, the orchards and the protection they provide for people, animals, and the environment, would disappear.

  • Steps are being taken to lessen the occurence of cork taint in natural-corked bottles. Major manufacturers have invested millions in recent years to screening their cork more carefully and upgrading their production processes.  As a result, cork taint rates have been dropping.

Besides all these practical reasons to refuse to move to synthetic corks, there’s a very deep psychological one.  The satisfying “pop” signals that a tradition almost as old as civilization itself is about to begin.  Wine is an organic, breathing substance.  It is its nature to change over time, and to change not in a formulaic way, but in a way influenced by its environment and the skill of those in charge of it.  To lock it behind machine-produced plastic is to lessen the artistry of wine aging.

  1. Curtis Maurand
    June 23rd, 2010 at 16:07 | #1

    If it doesn’t let wine out, then how does a natural cork let oxygen in? I can’t buy the whole oxygen in thing, especially when we talk about wine being in bottles for a couple hundred years and the bottles laying on their sides. Someone has to explain that to me.

  2. June 29th, 2010 at 18:53 | #2

    For starters, things which are liquid-tight are not necessarily gas-tight. So some oxygen filters in through the structure of the cork, but wine only wets the very end of it. Also, the cork (unlike a screwcap) can move in or out of the bottle slightly, in response to things like atmospheric pressure, temperature differences and the chemical processes occurring in the wine. These slight shifts can allow more or less oxygen (and CO2 and nitrogen, since air is mostly things other than O2!) into the bottle.

  3. jon r campbell
    February 14th, 2011 at 17:27 | #3

    I disagree completely (i also find it ironic that the same people that condemn the timber industry defend the cork one as a rtenweable resource, but that is besides the point)

    I have taken bottles off the line, smae wine, same day, all variables similar, and put cork and screw top wines in the sun, with a white pice of paper underneath, just to see if any drops happpen……

    the cork usually blows out of the bottle, while the screwtop not only was intact, but after further testing (cool down, heat up, never showed a problem)

    the cork didnt even make it through the first test, but somehow i should still believe it is a better enclosure?????

  4. Holly Snyder
    February 16th, 2011 at 14:24 | #4

    Cork is a renewable resource because it does not require killing the trees! Here’s more information about cork trees.

    The argument is not that cork is a more secure or durable closure, but that it is a BETTER one overall. Total air-tightness is not necessarily ideal, particularly for wines that will be aged long term. For wines that are drunk young, screwcaps are perfectly acceptable (and very common on a lot of Aussie wine).

    Unfortunately, once you’ve left your bottles in the sun, it doesn’t matter what you closed them with–they’re probably ruined regardless. No good wine should ever be left in the sun, so I’m not sure why this is the test you used to make your argument.

  5. Greg M
    August 13th, 2011 at 18:50 | #5

    He’s testing the effect on the cork, not the effect on the wine. The sun heats up the air and increases the pressure so you can see which fails under increased pressure and how quickly it fails. Of course there’s no need for a sealed bottle to hold in a great deal of pressure unless it’s a champagne bottle which is, of course, why they have wire cages. So the test is not completely invalid, but is probably holding the natural corks to a higher standard than they really need to meet.

    I do take exception to a variety of points in this article. Synthetic corks do expand and contract, just like any other substance. They are constantly trying to expand, just like natural corks which is what creates the seal in both cases. Neither undergoes thermal expansion and contraction remotely similar to that of glass, both, left to their own devices, would be much larger than the inside of the bottleneck.

  6. March 6th, 2013 at 10:54 | #6

    Thank you Holly (and Stephanie) for the commentary. I have 80 bottles of wine to do this weekend, my first batch ever. Google brought me here, you solidified my choice. Cork breathes, doesnt leech plastic chemicals into the wine and over time expands or contracts according to mild fluctuations that may occur in my newly build cellar. I will be using natural corks. Thanks for the information.

  1. February 23rd, 2010 at 22:19 | #1
  2. July 6th, 2010 at 15:58 | #2