Botrytis / “Noble Rot”

Botrytis or “Noble Rot” is a type of fungus that shrivels and days wine grapes. The gray mold is beneficial in some cases, intensifying grapes’ (and the produced wine’s) sugar level, and adding flavor and aroma.

Botrytis infestation requires moist conditions and humid or wet weather, however, some winemakers may choose to spray the spores of the fungus over the grapes in the vineyard to start the process.

The fungus permeates the grape skin, allowing water content in the grape to evaporate during dry conditions (shriveling up like a raisin). When this happens, the sugar content increases and is highly concentrated in the remaining juice.

Hungarians in the 16th century were the first documented to deliberately use noble rot in winemaking in Tokaj. The Germans also were early adopters with first records at Schloss Johannesberg around 1750. By 1830 this process was well established in the renowned Sauternes.

Some of the finest botrytized wines are picked and separated grape by grape. Some grapes are more prone to infection than others, likely due to the thickness of skin and the plant’s ability to produce antifungal compounds. Because this process can be so labor intensive, with such small yields, the sweet wines produced through Noble Rot are often relatively expensive. Wines such as Sauternes from Bordeaux, Tokaji Aszu from Hungary and Spätlese level German Riesling are all made from Noble Rot grapes. Tasting notes from these wines often include “honey”, “beeswax” and “vanilla”.