Is Bordeaux too hot for Merlot? As much of Europe sweats through another heatwave, Bordeaux wineries took a bold step last week, authorizing seven new wine grapes for Bordeaux AOC and Bordeaux Supérieur wines.

You might think this would be controversial in tradition-bound Bordeaux, but the vote at the wine producers' syndicate was unanimous. It still needs to be approved by France's national oversight body, INAO.

It's a huge move for one of the most conservative areas of the wine world. But it also is a recognition of a changing planet. Some Bordeaux vintners have been growing non-allowed grapes in their vineyards for several years as a hedge against climate change.

For now, the only wines that will be allowed to use these grapes are those with the entry-level Bordeaux or the geographic Bordeaux Supérieur labels. The famous appellations of Bordeaux, such as Pauillac and Saint-Émilion, will not be affected.

"I'm not completely surprised" by the new grapes, says Hortense Dernard, a Bordeaux native and general manager of Millesima, a New York wine importer. "There are more and more people who are doing a few rows here and there. They can't put Bordeaux on the label at all. Bordeaux moves a lot. The big day for me is when something will change in the (major) AOCs. And maybe that will never happen."

This move is as much about wine style – and winemaking regulations – as it is about farming.

Merlot is the most-planted grape in Bordeaux and is the bulwark of most red wines east of the Gironde river. The problem with Merlot in overly hot weather is not that heat is bad for the vines or the crop. In fact, Merlot in an overly hot year presents the definition of a first-world problem: it produces grapes that have too much sugar, so the wine has too much alcohol.

In California, where Merlot makes up a large percentage of red blends, many wineries turn that into a feature, making a high-powered wine. Or they just add water; when done surreptitiously, this is known as "washing the fermentation tank".

But in France, it's illegal to add water. And, while there is a market for big-bodied, high-alcohol Bordeaux wines, the majority of Bordeaux wineries still differentiate their products from New World wines by pointing to their elegance.

There are only so many ways French farmers can legally cut back on the alcohol content of their wines. Picking earlier is the easiest method, but there's a limit to how early a vintner can pick, because often the sugar that becomes alcohol develops in grapes faster than the flavor compounds that make wine delicious. Picked too early, a wine might taste like alcohol and tannin and not much else.

Different grape varieties ripen at different times, though. As the world warms, quality grapes that can stand more heat without ripening too quickly should become more popular.

The seven newly approved Bordeaux grapes, four red and three white, include two major Portuguese grapes, as well as a grape that is obscure in France but is one of the most popular red grapes in China.

The big name here is Touriga Nacional, perhaps the best grape in Portugal's hot Douro Valley. Touriga Nacional makes wines of great complexity and elegance even in hot, dry conditions. In fact, it's possible that its acceptance by Bordeaux will lead to greater adoption in other hot regions where it might perform better than Cabernet Sauvignon (cough-cough-Napa-cough).

Bordeaux's white wines are not as expensive or important to the market as its reds, but they will get a boost with the white grape Alvarinho, which makes terrific wines from the coasts of both Portugal and Spain.

The third-most important grape on the new list is Marselan, a cross between Cabernet Sauvignon and heat-tolerant Grenache created in a French research institute in 1961. Marselan appears in some southern French red wines but it is a major varietal wine in China. As popular as Bordeaux wines are in China, this would seem to be an easy sell.

The other four grapes are obscure. They are:

* Petit Manseng, a white variety usually used in sweet wines

* Arinarnoa, a cross between Cabernet Sauvignon and Tannat

* Castets, a rare red variety first identified in Bordeaux in 1870. It was down to less than one hectare in France in 2008, according to Wine Grapes by Jancis Robinson and José Vouillamoz

* Liliorila, a rare white variety that is a cross between Chardonnay and another obscure grape with the evocative name Baroque.

Don't expect to see these variety names on a Bordeaux bottle anytime soon. Growers are only being allowed to plant up to 5 percent of their vineyards with them, and can only add up to 10 percent in their final blend of any bottling.

Jeff Harding, wine director of The Waverly Inn in New York, says he doesn't think augmenting Cabernet Sauvignon, Merlot, Cabernet Franc, etc., in Bordeaux wines will affect sales.

"I really think most customers will give the benefit of the doubt to Bordeaux," Harding says. "A lot of people don't know that Muscadelle and Sauvignon Blanc and Semillon are in the whites. I think most people trust the Bordeaux winemakers because they've been doing it for centuries."

Denard says the new regulations are just an approval of experiments that are already happening – even in the most expensive vineyards in Bordeaux.

"There are some people who do some Carmenère in Pauillac," Denard says. "It's a well-kept secret. Everybody in Bordeaux is making more and more tests. You never know what tomorrow's going to be."

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