IT'S DIFFICULT to comprehend in a world where everything is available all the time, but until 1850 in Germany it was illegal to make beer with wheat. Bavaria's famous purity law of 1516, the Reinheitsgebot, forbade the use of any ingredient for brewing except water, barley and hops (they didn't yet know about yeast).

Most accounts suggest the reason for this was competition with bakers, who used primarily wheat and rye, to keep the price of bread affordable. Others have pointed out that the Bavarian royal family had a monopoly on barley and didn't want other grains spoiling their profits.

Finally the law was relaxed and brewers began making beer with as much as 50 percent wheat (with the remaining half being barley). The Schneider family was one of the first wheat beer brewers in Bavaria when they began in 1872 and today the Schneider Weisse Brewery still makes one of the finest examples.

Murky story

Since then, a number of wheat beers have become traditional German beer styles. The most well known style today is undoubtedly hefeweizen. The word "hefe" is German for "yeast," because these unfiltered beers have yeast swirling around each glass or bottle making them appear cloudy. You could filter out the yeast (and some of the remaining wheat, too) but you'd lose a lot of the beer's signature flavor. In fact, a filtered wheat beer that is not cloudy is called a "kristallweizen," but it's not nearly as popular as its murky cousin.

But the special yeast does something else that's very important. The yeasts used to make wheat beers are nearly wild and impart a signature aroma of bananas and cloves. You can make wheat beer with more common yeasts, but you won't be able to get the flavors of a true Bavarian-style hefeweizen.

A few years ago, Sierra Nevada Brewing in Chico obtained a unique yeast from a very small brewery in Bavaria. Head brewer for R&D Scott Jennings began playing around with the yeast in their pilot brewery to create a traditional Bavarian hefeweizen, a difficult task for a brewery making ales using English-style brewing methods. After several attempts that weren't quite perfect, Jennings came to believe the key was open fermention, the traditional way they're made in Germany.

Fermenting mystery

Most fermenting tanks in the U.S. are closed, meaning they can't be opened from the top, but Sierra Nevada did have four open fermenters in their brewery which they use for certain beers, such as Bigfoot. So Jennings, along with owner Ken Grossman and brewmaster Steve Dresler, flew to Germany to tour wheat beer breweries. The trip convinced Grossman and Dresler to let Jennings use their open fermenters, and the results, as Jennings puts it, were "night and day. This is it," he remembers — it gave the beer "the final polish we were looking for so long."

Sierra Nevada will launch its new hefeweizen, Kellerweis, nationally June 1, although it's already available in Chico and Reno. I was able to try an early sample of this beer and it's one of best examples of the style made by an American brewer. The aromas of ripe bananas and cloves are there, just as they should be, with hints of warm bread and bubble gum underneath. It's very refreshing as you'd expect but with full flavors and a rich creaminess. I think people will be surprised that a brewery known for big, hoppy beers has made such a delightfully unhoppy, traditional-style Bavarian hefeweizen, and made it so well.

More is more

Interestingly, another award-winning California brewery, Firestone Walker in Paso Robles, also has just launched a traditional hefeweizen. To brewer Matt Brynildson, the key to the style — and a major difference between U.S. attempts to make these beers — is "they need to have a creamy middle that's rich with malt flavor." When I had a chance to try an early batch at the brewery last month, I found that his take certainly accomplishes that. It's currently available only on draft at the Yard House chain (in nine states, but mostly Southern California) but expect to see it throughout Northern California this summer.

If you can't wait, other Bay Area brewers making this style include Drake's, Gordon Biersch and Sacramento Brewing. They're best served in a traditional tall half-liter wheat beer glass. The proper way to pour one is to tilt your glass and pour out roughly two-thirds of the beer into your glass. Then swirl the rest in the bottle by rolling it in your hands before emptying the remainder into the glass to get the full yeasty flavors. Probably the best place to enjoy a hefeweizen is outside in a beer garden. In Bavaria, before drinking, you must clink the bottom — or foot — of your glasses together and say Prost or Cheers!

Reach Jay R. Brooks at brooksonbeer@yahoo.com. Read more by at www.iba buzz.com/bottomsup.