Wine is not as fragile or sensitive to temperature as milk or juice, but it is perishable and must be properly sealed against the environment. Wine bottles have traditionally been sealed with natural corks covered by foil capsules, but today some wine makers use synthetic corks, screw caps, or boxes. Each has advantages and disadvantages; some wine traditionalists treat natural cork as the only appropriate way to seal wine bottles but you can comfortably buy wine sealed with synthetic cork, screw caps, or in a box.
Corks, Tradition, and Wine Ritual
Most ritual and anxiety associated with opening wine is connected with the natural corks traditionally used to seal wine bottles. Corks are not always easy to remove and this has probably contributed to the image of wine as an "elite" drink — if you have the skills to remove the cork quickly and easily, you will look very good doing it but if you don't, you may look foolish and even make an awful mess.
Anything this difficult to open well has to have something worthwhile inside, right? Yes, the wine inside should be worth your while, so it's also worth your while to learn how to open wine bottles properly. Fortunately it's not as difficult as it seems, so you you can look as good opening wine as anyone, impressing people with both your wine knowledge and your wine opening skills.
The traditional use of natural cork to seal wine bottles isn't because it's difficult to open, but rather because cork creates a permanent seal for extended aging. Made from millions of hollow cells joined together by strong membranes, cork can be compressed for insertion into the bottle then it will expand to fill the space, tightly sealing the bottle for decades. Nothing else over the past centuries has been discovered that performs this function as well as naturally grown cork, about 90% of which comes from cork oaks grown in Spain and Portugal.
Synthetic Corks, Screwcaps, and Boxes
Because cork is most critical when aging wine over several years, it isn't quite as necessary for wines that aren't meant to be aged. This is why there are more options available now for all the wines which are meant to be drunk a few months to a couple of years after purchase. Wines with corks made from synthetic materials can be kept a bit longer, maybe three or four years, while wines with screw caps are already a bit old at two years.
Wines in boxes, though, have lives that can be measured in months. No one will be proudly showing off a box of Zinfadel that's been aging in their basement wine cellar for 20 years. Boxed wine has something of a negative reputation today, but that's largely because many of the first boxed wines simply weren't very good. Today, the processes for packaging boxed wine have advanced to the point where it's possible to produce acceptable boxed wine — it still isn't high quality, never mind exceptional, but they are good values for acceptable, casual wines.
The use of cork, screw caps, or other materials to seal the wine bottle isn't a sign of a wine's quality to the degree it was a few year ago. It's entirely possible for a wine with a screw cap to be better than a wine sealed with natural cork, just so long as it hasn't been sitting around for a long time. It all comes down to what sort of wine you are purchasing, what purpose the wine will be served for, and when you intend to drink it. If you want a high quality wine which you can cellar for a few years, you need natural cork; if you want a good value for a party, there are a lot of good options for boxed wines.