(SFExaminer) - Ten years ago, people were just starting to get used to the idea of premium wines with screw caps. Now, wine on tap has pushed things further as many top producers are now selling wine in kegs, often to very good restaurants.

You might wonder, what’s the rub?

This is how it works: Wine is aged in the barrel or tank. Then instead of going to the bottling line, it’s put in lined metal kegs. Like beer, every time wine is dispensed the empty space in the chamber is filled with argon, nitrogen and/or carbon dioxide to prevent the wine from oxidizing. This allows a restaurant to pour from the same keg for days or weeks without worrying about spoilage.

From an environmental point of view, an enormous amount of glass is used every year to bottle wine, even with recycling. There are different sizes of kegs, but the industry standard, 19.5 liters, is equivalent to 26 bottles of wine — more than two cases of glass bottles.

So if wine on tap is such a great way to go, why doesn’t everyone make the transition? Kegs work well for wines that are not meant for long-term aging. The beauty of cork is that it is pervious to oxygen, which is important, to a degree, in wines that take years to reach their potential. A Barolo that is stuck in a completely oxygen-free environment will not evolve properly. However, a young nebbiolo — the grape used to make Barolo — that is not going to have a shelf life of more than a couple of years is an ideal candidate, so the logic goes.