Turning Grapes into Gold: A Strange Alchemy in Bordeaux

Posted on April 4, 2014 Updated on July 2, 2015

Early April is the start of en primeur in Bordeaux, when many of the region’s producers open up their cellars to the world’s wine buyers and critics for an official first taste of barrel samples from the previous fall harvest. By all accounts 2013 was a difficult year for the dry reds, with none of the famed estates of St.-Émilion, Pomerol or the Médoc being spared. For whites, however, and in particular the famous botrytized dessert wines of Sauternes and Barsac, it was a stellar vintage. So, what exactly happened that made it such a great year for sweet whites? What does it take to turn out superb Sauternes and Barsac?

Whether white or red, good wine starts with healthy grapes. In Bordeaux, situated as it is along the temperamental Atlantic coast, so much of keeping grapes healthy depends on that most banal of all conversation topics: the weather. It is no small matter here though, where fortunes can change with the crack with a lightning bolt. And last year Mother Nature threw everything she had at the vines. A cold, wet spring delayed flowering until mid-June. As a result, pollination was spotty, with a lot of failed fertilization (coulure) and uneven fruit set (millerandage). Right out of the gate there was going to be reduced crop for everyone. For producers of sweet whites this was manageable since yields need to be low anyway (a maximum of 25 hl/ha vs 40 hl/ha for classed-growth reds). Reds too could have recovered from this, but storms and hail in late July/early August destroyed a good portion of the crop, while miraculously bypassing Sauternes and Barsac. What little was left of the red grapes was then beset by humid conditions that fostered the growth of mold and mildew. Of course, this was just what the white grapes for sweet wines needed.

Fickle Fungus

The key ingredient, and what distinguishes the dessert wines of Sauternes and Barsac from those made from late-harvest or dried grapes, is the unsightly, ash-like mold Botrytis cinerea (noble rot). As the fungus spreads over the grapes its filaments pierce the skin, causing the water to evaporate, which in turn concentrates the sugars. As it works its way inside, it interacts with the grape’s contents, consuming acids, extracting tannins from the skin, and producing glycerol, which plumps up the viscosity. The wines are rich and unctuous with layer upon layer of complexity. Semillon is the principal grape used (80%) since its thin skins make it particularly susceptible to botrytis infection, and it gives the wine a rounder, fuller body and lanolin/honey-like notes. Sauvignon Blanc is used in lesser amounts (20%), mostly for its acidity, but it too will succumb to noble rot even though its skins are thicker. Muscadelle appears in minute amounts, but growers find that its grapey aromas, nice though they are, aren’t worth the trouble.

Getting botrytis to grow, however, is never a sure bet. Although its spores are present during the flowering stage, it’s not until early fall when the grapes have ripened that the fungus springs to life. But only under the right conditions: namely, misty autumn mornings followed by warm, sunny afternoons. Where these conditions happen most frequently is about 25 miles southeast of the city of Bordeaux, where the warm waters of the tidal Garonne River meet the cool, spring-fed Ciron. The difference in water temperatures creates nighttime mists that fill the surrounding hills of Sauternes and Barsac. With luck they’ll be burned off by the afternoon sun, further desiccating the grapes and keeping at bay the less-beneficent gray rot and other molds. This is precisely what happened last fall, except that humid conditions blanketed the entire region, infecting the red grapes with grey rot.

Of course, even when botrytis does take hold it doesn’t necessarily do so evenly. Since only fully affected grapes can be picked, harvesting must be done hand, usually with successive passes (tries) through the vineyard over the course of a few weeks. The area’s most prestigious producer, Chateau d’Yquem, has been known to make as many as 13 passes, which goes some way in accounting for the three-figure price tag for half-bottles of an off year. Here again the weather can wreak havoc while waiting for botrytis to develop. Rain at this time is particularly dangerous as it invites the growth of malicious gray rot and other molds, which would destroy the grapes entirely. Growers must constantly keep their eye on the forecast with their fingers crossed while they wait for this finicky fungus to do its magic.

It’s a risky, nerve-wracking business, and on average the winemakers of Sauternes and Barsac can expect only a few good vintages per decade. Just the year before, in 2012, conditions were so unfavorable to the development of botrytis (two months of drought followed by a downpour) that Yquem declared it would not be making its grand vin at all. Rather than risk its reputation, Yquem decided to take a $33 million hit. Millions of dollars lost to the vagaries of the weather.

Outstanding Sauternes/Barsac Vintages: 2011, 2009, 2005, 2001, 1990, 1989, 1988, 1986, 1983, 1967, 1962, 1959