Noble Rot, Explained: How the World’s Great Sweet Wines Are Created by a Finicky Grey Fungus


Legendary sweet wines Sauternes and Tokaj both get their flavor from the grey fungus Botrytis cinerea, which concentrates a grape’s flavors and sugars

Despite their bad reputation, mold, yeast, and fungus are responsible for some of the tastiest things in our lives, such as blue cheese, bread, pizza crust, soy sauce, miso, and of course mushrooms and truffles. As wine lovers, we can’t forget Botrytis cinerea, the grey mold known as Noble Rot that under the right circumstances can affect grape bunches to create ethereally sweet wines such as Sauternes, Tokaji Aszu, and Spätlese and Beerenauslese Riesling. It takes perfect conditions for botrytis to work its wonders; if the season is simply wet, the mold will ruin the grapes or any other fruit or vegetable that it grows on, rendering them inedible or useless for winemaking.

However, a period of humidity, especially cool, foggy mornings, followed by a dry spell before harvest creates an ideal situation. The fungus dehydrates the grapes, which increases the proportion of fruit sugars and acids, offering a sweeter, more intensely flavored berry from which to make wine. Affected grapes shrivel to the point that they look like raisins, but when a portion of these berries is added to “healthy” grapes during the fermentation process the result is a complex, sweet, full-textured wine. Made properly, vibrant acidity will offset residual sugar, resulting in a wine with excellent balance and equilibrium.

Sauternes, Barsac, and Tokaji, which we focus on here, are the primary sources of easy to locate Noble Rot wines. In addition, Germany, Austria, Alsace, and many other cool, humid regions around the world make botrytized wines from a variety of white grapes including Riesling, Gewurztraminer, Pinot Gris, Sauvignon Blanc, Semillon, Furmint, and Chenin Blanc. Botrytis and red grapes are not good partners; the same conditions that create delicious, sweet white wines would induce unpalatable flavors if made into wine using red grapes.

Sauternes and Barsac

Chateau Rieussec noble rot

Situated within the larger confines of Bordeaux, Sauternes and the wholly contained sub-region Barsac are home to about 140 wineries. Their 4,700 acres of vines represent only two percent of the total area of Bordeaux, but locals are quick to point out that they garnered 27 grand crus in the famous 1855 classification. In 1939, both Sauternes and Barsac were among the first French AOC appellations to be registered. The five communes that comprise this area are Barsac, Bommes, Sauternes, Fargues, and Preignac.

Winemakers in AOP Barsac have the choice of labeling their wines as AOP Barsac or AOP Sauternes; the requirements for both are the same. The three grapes authorized for use to create these specialized wines are Semillon, Sauvignon Blanc, and Muscadelle. Generally, 80 percent of the grapes used in the finished wines are Semillon, 20 percent are Sauvignon Blanc, and only a very small percentage is Muscadelle, but the last grape can be very important for powerful aromas. Five million bottles are produced annually and 30 percent of those are destined for the export market.

These two regions owe their success to the temperature differences and proximity of the Garonne and Ciron Rivers. The contrast creates morning fog, condensation, and mist at their confluence that is necessary for the growth of Botrytis cinerea. These misty mornings and sunny afternoons facilitate the growth of this microscopic fungus, which gives the wine its unique flavor and texture. Because the botrytis does not form at a uniform rate, winemakers must pass through the vineyards multiple times to pick only the most botrytized grapes each time. The process of making these wines is very labor intensive and therefore makes them more expensive compared to other styles of sweet wines.

Sauternes and Barsac wines will exhibit aromas of orange, lemon blossoms, passion fruit, and mango. You will find flavors of orange and apricot marmalade, toasted pineapple, and soft hints of baking spices. There are also touches of beeswax and acacia honey flavors with full-on mouthfeel and a finish that is equal parts vivid and sweet. Notable producers include Château d’Yquem, Château Rieussec, Château Climens, Château de Fargues, and Château Caillou.

These wines are often enjoyed with foie gras or blue cheese as well as tarts and pies made with apple, peach, or pear. Sauternes and Barsac also work well with fried or roast chicken, brined and grilled pork chops, and pasta or risotto made with butternut or acorn squash.

Tokaji AzsuRoyal Tokajis St. Tamás

Northeast Hungary’s Tokaji-Hegyalija region is famous worldwide for its highly prized sweet wine blend called Tokaji Aszu, which is made from botrytized Furmint, Harslevelu, and Muscat Blanc grapes. Situated at the confluence of the Bodrog and Tisza Rivers, the Tokaji region is known for the heavy fog that covers the vines in the mornings during grape growing season. This high humidity moisture fosters the occurrence of botrytis and supports its growth.

This delectable, sweet wine has been a favorite of noblemen, poets, and artists for centuries and was called the “The King of wines, the wine of Kings” by Louis XIV. Voltaire was said to have waxed poetically about Tokaji Aszu and Pope Benedict XIV was reportedly heard to say, “Blessed be the land that has produced you. Blessed be the woman that sent you. Blessed be I who drink you.”

Unaffected grapes are first harvested in September to make the base wine and other grapes stay on the vine to become inoculated with botrytis. These grapes will shrivel, and their sugars will concentrate until the second picking in late October or November. Harvested botrytized grapes are gathered in large baskets known as puttony and added to 136-liter barrels of base wine. The number of baskets of sweet grapes added to the base wine gave the Tokaji Aszu the Puttonyosrating of 3, 4, 5, or 6 Puttonyos, with 6 Puttonyos as the sweetest on the Puttonyos scale.


Under current regulations winemakers now make only late harvest Szamorodni, 5 Puttonyos Tokaji Aszu, 6 Puttonyos Tokaji Aszu, and Eszencia. A Tokaj wine made from only botrytized grapes is known as Eszencia. For a Tokaji Aszu wine to be labeled today as 5 Puttonyos, it must have at least 120 grams per liter of residual sugar and a wine labeled as 6 Puttonyos must have at least 150 grams per liter of residual sugar. An Eszencia wine can be as sweet as 450 grams per liter and is a very rare and expensive commodity.

Tokaji Aszu wines have aromas of honeysuckle, jasmine, beeswax, and peach. You will find flavors of canned apricots, caramelized pineapple, tropical fruits, and white flowers with velvety mouthfeel and well-balanced acidity. Look for bottles from Oremus, Royal Tokaji, Diznoko, Chateau Dereszla and Patricius.

Tokaji Aszu goes with a wide variety of foods, so please don’t just relegate it to dessert. While it is delicious with ice cream or crème bruleé, it also pairs beautifully with savory foods such as duck or goose pâté, dishes made with gorgonzola or other blue cheeses, or spicy foods like Thai curries. It’s also a special treat with Peking Duck.


Source: Noble Rot, Explained: How the World’s Great Sweet Wines Are Created by a Finicky Grey Fungus