Marketers long have viewed water as one of beer's strongest selling points. Remember when Pearl hailed "from the country of 1,100 springs"?

Malt, too, is a familiar concept, if only because of malt liquor. And in recent years brewers have responded to Americans' enthusiasm for bitter, aromatic hops by giving their beers such names as Hopsickle and Modus Hoperandi or bragging that they're "triple-hopped." Without a string trimmer luckily!

But beer's fourth ingredient often gets overlooked, a situation that Houston brewer Brock Wagner hopes to change.

Let us now raise a glass to yeast.

"People don't understand yeast character," said Wagner, head of Saint Arnold Brewing Co. "Everyone is so busy talking about malt and hops. Let's educate people about yeast."

Saint Arnold is announcing today a new "Movable Yeast" series, a planned quarterly release of familiar beers fermented with different yeasts. First up will be a small batch of Weedwacker, a variant of the brewery's biggest seller, Fancy Lawnmower. The beers will be identical, except that Weedwacker will be made with a Bavarian hefeweizen yeast that is expected to give it a pronounced wheatlike flavor.

"A lot of people, they think they're tasting wheat," Wagner said. "It's the yeast they're tasting."

The draft-only Weedwacker is scheduled for release Aug. 16. Wagner is encouraging bars and restaurants to offer it and Lawnmower side by side so people can appreciate the differences and learn a little bit about what goes into their beer.

It'll be a rare star turn for an otherwise unglamorous fungus that gives ales and lagers their personality — as well as their kick.

Standard formula

The home-brewer in his garage and the head brewer down at the Budweiser plant follow the same basic formula: they mash water and malt into a pre-beer mixture called wort and then add yeast, which goes to work devouring sugars and turning them into alcohol, while emitting CO2 for carbonation and adding other flavors and aromas.

Yet for most of beer's 10,000-year history, yeast went about its business anonymously. People knew they liked beer, but they didn't understand the debt they owed to naturally occurring yeast. They didn't even know there was such a thing until the invention of the microscope.

"One of the first things they put under the microscope was beer," said Chris White, who runs White Labs, a San Diego laboratory that cultivates and sells yeast strains to small brewers, winemakers and distillers.

These early scientists, White said, could see yeast but regarded it merely as one of several byproducts of fermentation. It wasn't until the 1860s that Louis Pasteur proved what yeast was up to.

That allowed breweries and, later, laboratories to begin tailoring strains of yeast to produce specific tastes and various alcohol levels and to maintain consistency between batches of beer. Almost none of the brewer's yeast used today occurs naturally in the wild.

"Small changes in the yeast make huge differences in the way the beer tastes," White said.

Still, most people hear "yeast" and think of bread-making - or worse.

White knows this from the puzzled expressions he encounters after telling people that he works with yeast for a living.

"I've never figured out a good way to say it without getting strange looks," he said. "I do get a different look from women than I do from men. It's just different. Women have a completely different experience with it."

For the record, he notes, brewer's yeast doesn't cause disease. But it's easy to see why "yeasthead" never caught on as a catchphrase the way "hophead" did.

A perfect blend

Even people who make beer can underestimate yeast's critical role, said Scott Birdwell, owner of Defalco's Home Wine & Beer Supplies. He recalls one get-together in which a group of home-brewers made 14 batches of beer, identical except for the yeast.

The result was 14 very different beers.

"Here it was the same malt, the same hops, the same water," Birdwell said. "It was just weird. I think people were really surprised. It was a real interesting experiment."

Wagner recalled his nearly yearlong search, before opening Saint Arnold in 1994, for a yeast that would yield precisely the creamy, fruity flavors he liked. He finally got hold of one that originally had been used by a brewery in the south of England. It also accentuates malt characteristics and is hardy enough for higher-alcohol beers.

The company now contracts with two producers, including White Labs, to supply it with this exclusive strain, which is used in the production of six of Saint Arnold's five year-round and five seasonal beers. The house yeast is durable, too; a single batch can be used up to 20 times before it degrades.

Wagner acknowledges that a promotion as esoteric as "Movable Yeast" is "not going to be something everybody is going to want."

But the success of the brewery's Divine Reserve releases - the last two sold out quickly - suggests that consumers are game for trying something new.

That kind of experimentation is a big part of what motivates home-brewers, and Birdwell said he's glad to see the guys at Saint Arnold, who have struggled to keep up with demand since moving into a larger facility earlier this year, get to the point where they can tinker on a commercial scale.

"They're having some fun now," he said.

ronnie.crocker@chron.com