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Weir, owner and winemaker of Napa's Hagafen Cellars, alongside Mount Maroma by St. Supery in Rutherford, Sonoma's Gan Eden Winery, and the Baron Herzog California label, is revolutionizing kosher wines.

They're not, as one wine-industry insider cracked, "your mother's kosher wine." Forget about boysenberry — those four cups at Passover will never taste the same.

Says Weir, "I am making Napa Valley wine, and the wine happens to be kosher."

Steve Elprin, managing director of wine for the S.F.-based J. Sosnick & Son kosher food and specialty distributors, says the new wave of kosher wines are good enough to wash down many more meals than seders.

"These wines should be able to be sold on their own merits, as chardonnay, as cabernet, as good wine."

Slowly, Jewish wine-drinking habits are changing, and the evolution often starts at Passover, after people have downed that fourth glass and discovered it wasn't Concord.

"There are so many people I talk to who go to seders and say, `I had this cabernet and it was great!'" Elprin says.

That's a message Weir and his competitors have been cultivating for years in order to win over Jews and non-Jews alike. They have built reputations as serious producers, winning wine competition medals and top wine press reviews, helping to stamp out the notion that kosher means only Manischewitz.

But it's rough new ground those winemakers are blazing. While the U.S. premium wine industry is booming at more than $8 billion annually, kosher wines claim only a sliver of that world's wine turf — an estimated three-tenths of 1 percent.

"If we could get 1 percent, it would be wonderful," says Peter Stern, the Saratoga-based winemaker for Baron Herzog of San Martin.

The winemakers must do more than prime the public's palate for kosher wine. Major buyers — supermarkets and wine shops — usually stock up on kosher wines just before the holidays, Elprin says. As a result, the top kosher winemakers rely on the first three months of the year, before Passover, for about half their total annual sales.

As Hiram Simon, a consultant and seller at Berkeley's Wine Wise puts it, "There's no question that it takes a lot to dislodge this mindset, that it's wine as a sacrament rather than a beverage with a meal."

So the winemakers are crafting their individual products in different ways to elevate people's preconceptions about kosher wines.

Weir stood in his vineyard one day recently and gestured toward the lush green valley and rolling brown hills around him.

"Napa Valley has the highest regard among wine drinkers," he says, calling his product "the best wines that are kosher in Napa Valley."

Therefore, he adds, "they are the best ones around."

Now in its 17th year, Hagafen (Hebrew for "fruit of the vine") is replanting and upgrading its vineyards, and Weir plans to open his own winery on his Silverado Trail land in 1998. He is also developing a World Wide Web site, and aims to move 12,000 cases (12 bottles per case) this year of cabernet, cabernet reserve, pinot noir, chardonnay, chardonnay reserve, Johannesburg riesling and white zinfandel.

North of Hagafen in the mid-Napa Valley town of Rutherford sits St. Supery, owned by the French Jewish Skalli family corporation. The winery, which in 1993 began selling Mount Madrona cabernet and chardonnay (and has since changed the name to Mount Maroma, or "higher place"), will produce 3,500 cases of the wine world's two most popular varietals in new, improved oak barrels by year's end.

St. Supery, which offers kosher wine tours by appointment at its Highway 29 Wine Discovery Center and has a Mount Maroma Web site as well, also sees its kosher label as uparalleled.

"We have quite a nice little niche here: We're only one of two kosher Napa Valley wines," says Sandy Flanders, St. Supery's marketing director.

To the west, in Sonoma's Green Valley town of Sebastopol, lies Craig Winchell's Gan Eden Winery. Winchell, who started Gan Eden ("Garden of Eden") in 1985, is the biggest of the boutique kosher wineries, producing about 25,000 cases annually. This year he's uncorking a cabernet, a chardonnay, a late harvest gewurztraminer and a black muscat dessert wine.

Winchell, who as an observant Jew operates California's only strictly kosher winery, is releasing a 1990 cabernet only this year, and still sells a 1989 cabernet.

"I hold my wines back a long time," he says. "I make distinctive wines that people either love or hate. I don't compromise everything to get a wine that everyone enjoys but no one goes ape over."

These cutting-edge kosher winemakers work in the shadows, however, of Baron Herzog, owned by the New York-based Herzog family's Royal Wine Corp. (whose Kedem, along with rival Manischewitz, makes about 2 million cases annually of the more traditional sweet wines).

Today Herzog produces 120,000 cases a year under its Baron Herzog California label, plus another 25,000 under the Weinstock Cellars label, formerly owned by Geyserville's Robert Weinstock. Royal also owns the smaller J. Furst label, and imports French, Israeli and Italian kosher wines too.

Like Gan Eden, Hagafen and Mount Maroma, Baron Herzog over the years has consistently captured many wine competition medals. Herzog has spared little expense to market its products, hosting events such as an Haute Cuisine Pre-Passover Seder at San Francisco's St. Francis Hotel last year, where top wine journalists munched on dishes such as veal cocotte and sipped wines including cabernet and merlot.

Though Herzog winemaker Stern dislikes the comparison, the smaller winemakers agree that Herzog — in sheer marketing muscle, if not quality — is the kosher wine world's cousin to Ernest & Julio Gallo.

Herzog, says Weir, "is the biggest, the most serious player" in kosher wines.

This year, its 10th producing California wines, Herzog is offering a limited edition 1994 cabernet and reserve cabernet, a late harvest riesling, a cabernet, chardonnay, chenin blanc, gamay and white zinfandel.

Herzog has also formed what Stern calls "strategic alliances" with several French winemakers, and is importing super-premium kosher wines in the $40-$55 range by Chateau Giscours Margaux, Chateau La Gaffeliere, Chateau Yon Figeac, Chateau Clark and Chateau Piada. The wines include cabernets, a merlot-cabernet franc blend, a St. Emillion and a sauterne.

"This," Stern says of the top-flight French imports, "will really help turn around the kosher image."

Herzog is not the only producer for whom kosher wines are a two-way street between California and Europe. Skalli imports a kosher chardonnay and merlot under the Fortant de France label, which sell in the "fighting varietal" price class of around $8 per bottle, and Wine Wise imports the kosher Domaine Bunan of Bordeaux that retail around $14.

Swelling the kosher wine market is Korbel Champagne Cellars in Sonoma's Guerneville, which is introducing the Korbel Kosher Brut Champagne, the first premium sparkling wine certified by the Union of Orthodox Jewish Congregations.

While the French wines could gain a foothold in the domestic kosher wine world, much of the battle for kosher wine standing revolves around kashrut itself. The war is, literally, over heat.

Among the claims to fame by Hagafen, Mount Maroma and Herzog are that their wines are mevushal, or cooked. In fact, they are flash pasteurized at 185 degrees for several seconds by a machine one St. Supery worker lovingly calls a "mevushalator."

The process allows observant Jews to drink the wine no matter who is pouring it. That is crucial not only to gain the coveted "circle U" or U.O. — the Orthodox Union's widely accepted stamp of kashrut (and costly to winemakers, boosting the wine's price). It also opens the door to kosher catering sales and to a burgeoning modern Orthodox clientele that is thirsting for good wines, Weir and others say.

Mevushal's roots reach to the Babylonian era of the sixth century BCE, a time of intellectual and social freedom in Mesopotamia when Jews and non-Jews freely mixed — and shared sacramental wine. To counter the threat of assimilation from such social intercourse, rabbinic authorities had wine boiled.

The wine then could be used for religious purposes, but was not in great demand as a social lubricant. Non-boiled wine could still be shared between Jews, but only yayinmevushal (boiled wine) could be accepted from non-Jews.

Today, the debate over mevushal depends on who is doing it. Winchell, as an observant Jew, meets the other major benchmark of year-round wine kashrut because he personally makes his wines (to earn the circle-U, a wine must be handled during its production only by Sabbath-observant Jews). Other winemakers hire observant Jews, called mashgichim, who are supervised in the winemaking. All the kosher wines also forgo traif additives such as some animal-based yeasts.

Thus Gan Eden avoids the mevushal process, which Winchell maintains alters a wine's taste. "With mevushal, there is the potential to ruin the wine," Winchell says. "You are going to change the wine in some way."

Weir at Hagafen disputes that. Weir, who grows some of his grapes, and like Baron Herzog and Gan Eden acts as a negociant to purchase other grapes from key viticultural regions, makes his wines mevushal at St. Supery (but produces his wines at Napa Cellars in Oakville).

"I have been converted to mevushal," Weir says. "I've just seen enough science, and tasted enough wines, to see that it's fine."

In fact, Elprin and others say some leading French winemakers have long pasteurized their wines to filter impurities; Weir cites enology studies at U.C. Davis and elsewhere that show no ill effects from mevushal — and says that it even makes the wines clearer.

"It is not pasteurizing that is improving or harming the quality of the wine," Weir adds, holding a pinot noir vine in his vineyard. "It is the quality of the grapes that improves or harms wine."

So while these winemakers jockey for top kosher wine status, they still see their maneuvering as a victory for kosher wines.

"If people want to make quality wine that is kosher," Weir says, "it will only speak well for all of us."