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.

For every venue with a quality wine list that serves wines on tap, there are places that use it as a gimmick. Some of the wines are still good, yet I can’t help but question the motivation. As there are superb wines available on tap, there are plenty of nasty ones, too. These wines usually find a home, so how do you know which ones are worthy? It is the same as wine in bottles. The overall nature of the wine list should be your guide.

The best wines available on tap:

Broc Cellars Cabernet Franc, 2011 (Paso Robles): Chris Brockway has become a mentor to other aspiring natural winemakers in California, and his cabernet franc is one of the reasons why. A little spicy with floral overtones, red peppers and red fruits, it is one of the truest cab francs made in California.

Skylark Medianoche, 2009 (Mendocino County): With a wink to Priorat and Montsant in Spain, this syrah, cabernet sauvignon and grenache blend is not just another quaffer. Rich with blackberries, chocolate and black peppers, the two sommeliers behind this wine, John Lancaster and Robert Perkins, do the Catalons right.

Verdad Cellars Tempranillo, Roja Red, 2010 (Central Coast): A blend of 75 percent organic tempranillo and 25 percent sustainably farmed syrah, this gem is only available in kegs. Spicy, fruity and bright with cherries and spice, you might as well order a carafe because one glass goes down way too quickly.

Pamela Busch is a wine writer and educator who has owned several wine bars in San Francisco, including Hayes and Vine and CAV Wine Bar & Kitchen.

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