I remember as a teenager knowing that there were two sorts of wine; the "table wine" my parents drank with dinner or just before. Wine that came in large green glass bottles (hence the name "jug wines") with a screw-cap, for "every day," and the "special" wine they had when my mom made "company dinners" and invited guests. Now of course, I know that it's not that simple. There are natural corks, artificial, plastic corks, and screw-caps, and increasingly, even the wines in the fifty dollar a bottle and up range are using screw caps. I've not seen the large green glass bottles though; I suspect jug wine has been replaced by box wine.

There seem to be two issues here. First, the desire to avoid the dreaded "cork taint," and second, certain pre-conceived assumptions about "good" wine having a cork. You know the ritual depicted in films; the sommelier brings the towel-wrapped bottle of wine to the table, removes the cork one-handedly with a flourish, proffers it to the person he thinks has the correct status, and pours a sample in a glass to be swirled, sniffed, and sampled, with either a "yay" or a "nay."

The sniffing-and-examining-the-cork bit is all in aid of determining if the cork is dry (suggesting a bad seal) or if it has "cork taint," which, honestly, you really probably need to check the wine for, to be sure (hence the swirling-and-tasting, in case there's cork taint, oxygen damage, sulphur odors), etc.) Cork taint is caused by a chemical 2,4,6-trichloroanisole (TCA) present in some (but not all) corks. TCA is produced by microorganisms that live in the cork. TCA causes a "musty" odor and odd taste, ranging from a faint impression of the wine being "off," and slightly reduced flavor, to a an odor that is reminiscent of musty cellars and old books, and a flavor that is just wrong. Even very small amounts of TCA can be detected by the average person, either; as little as 5 parts per trillion is enough. That's a minute amount, which shows you how strong the effect of TCA is. Estimates of how much wine is affected by cork taint (or "corked") are slippery. The numbers I'm seeing range from 5% to 10% of bottles sealed with natural cork end up being "corked." In addition, there are problems caused by the basic nature of cork as a natural product, and the varying quality of individual corks; some don't seal quite tightly enough, which means oxygen can spoil the wine, creating other sorts of damage.

One alternative is to use artificial corks made of plastic. There are problems with artificial corks though. The plastic isn't reliable over time; chemical components change, the artificial cork becomes permeable, and the seal changes, allowing in oxygen. Thus far artificial cork technology has not produced a cork that keeps a seal as well as natural cork, but which is still removable. Right now, artificial corks are only used with wines that are expected to be consumed in a year, possibly two; so-called "early drinking wines. "

The other alternative is the screw-cap, sometimes called a "Stelvin." As my childhood memories from . . . well, more than a few decades ago attest, wine has had screwcaps for a very long time. In general though, they've been used on wines meant to be drunk fairly soon, not lovingly stored for ten, twenty, or even thirty years. The screw-cap does create a tight, reliable seal, better, even, than cork, and it's still very easy to open. Current Stelvin scewcaps are higher quality, with special liners. The irony here is that wineries and oenophiles interested in producing and drinking higher-priced wines are concerned that the screw-cap seal may be too tight. Cork is an natural substance and even a properly sealed cork allows some interchange of gases (including oxygen). We don't know, in terms of twenty or thirty years, if that slight interchange makes a difference in terms of aging wines. There simply hasn't been enough research.

Corks for bottles are one of the main industries for cork forests in Portugal and Spain. Cork is a renewable resource; the cork is really the thick bark of a tree. The trees are never cut down, since their bark can be harvested every ten years or so. But if the demand for corks drops, those lands and trees may well be destroyed in favor of another more lucrative use.

That said, screwcaps are used, extensively, for South African, Australian and New Zealand wines. I note that the "New Zealand Screwcap Wine Seal Initiative" asserts that the screwcap is perfect for even long-lived wines, citing Australian winemaker and author James Halliday

"Some people have the idea that the development of wine with a Stelvin (screwcap) closure will be artificially arrested. Not so; there is sufficient oxygen in the wine and in the head space to allow that part of development which requires oxygen to take place. And—what is more—much of the development takes place anaerobically (i.e.: without oxygen)."

Screwcaps are increasingly popular in Europe as well, on German, French (even reds!) and Spanish wines. In the U.S. it's far more common to see a screwcap on white wines (less likely to be aged by the purchaser) than on reds, though I note many California wineries are using them on both, and on wines designed for long-lives; Bonny Doon is an unabashed evangelist. In Washington I note that Stonecap Wines uses screw-caps, as does Hogue Cellars, and Pacific Rim, the Washington sibling of Bonny Doon. Pacific Rim praises screw-caps for their seal, and for their recyclability. Hogue is downright evangelical about the virtues of the screwcap. Hogue conducted a careful thirty-month comparative study, before deciding to put all their wines in carefully selected screwcaps.