Requirement #1: Special Climatic Conditions
For Botrytis Cinerea to become noble rot it needs a period of early morning humidity followed by warm, dry and sunny conditions. The humidity is often early morning mists generated from nearby lakes and rivers. This humidity fosters the ideal environment for botrytis cinerea to attack grapes. Subsequent late morning or afternoon warm, dry and sunny conditions will dry off the grapes to ensure that the botrytis infection does not become malevolent, but rather becomes the benevolent noble rot.
The humid conditions enable the fungus to spread through the grapes. The warm, dry, sunny conditions prevent the occurrence of 'bad' rot which cause the grapes to speckle first, then darken and eventually shrivel. This also causes the grape to shrivel the botrytis fungus inside each infected grape, and actually change the composition of the grape. Grape acids and sugars are concentrated, and the flavor and aroma compounds are also chemically changed.
Requirements #2: Grape Characteristics
Grape varieties most susceptible to noble rot are thin-skinned varieties with tight clusters. The thinner the grape skin the easier it is for the fungus to break through the grape, and the tighter the cluster the easier it is for noble rot to spread throughout the cluster. Examples of thin-skinned varieties susceptible to noble rot include Riesling, Semillon, Chenin Blanc and Furmint.
In French Noble Rot is known as Pourriture Noble and in German as Edelfaule.
From the Vineyard to the Wine
Because Noble Rot attacks individual berries, grapes destined for making botrytised wine are harvested individually by hand. This necessitates several passages through the vineyard, as the berries become infected at different times. This is both costly and time consuming.
The juice from 'noble rot' grapes is extremely concentrated and very high in sugars. As such, fermentations are slow and challenging for the yeasts to convert all the sugar to alcohol. While the exact process for vinifying botrytis style wines differs between regions, in most cases the yeasts die off well before all the sugars have been converted into alcohol, resulting in a naturally very sweet wine.
However, because noble rot also concentrates the acids in the juice, these wines have a wonderful acidity-sweetness balance, which makes them refreshing rather than cloying or syrupy.
The Taste of Noble Rot / Botrytized Wine
While there are very distinct differences between the botrytized wines made from different grape varieties and from different wine-growing regions, they all share some common aromas and flavors. This includes aromatic intensity reminiscent of orange marmalade, dried apricots, honey and a distinct savory, earthy fresh mushroom characteristic which I liken to smelling the underside of a freshly picked platter mushroom.
Reasons Why Noble Rot Style Wines are Expensive
The ideal climatic conditions that create noble rot do not happen consistently every year. This means that these wines can be quite rare. Harvesting the grapes individually is labor intensive, time consuming and expensive, especially when you take into account the potential volumes. Additionally, because Noble Rot dehydrates and shrivels the grape, the grapes yield very little juice. The combination of these reasons means that the production costs of noble rot wines are very high, rendering them expensive. But a little taste can go a long way!
Key Styles of Noble Rot Wines Around the World.
As mentioned up top, the two most famous noble rot style wines are Sauternes (from Bordeaux, France) and Tokaji Aszú (Hungary). Also legendary are the TBA (Trockenbeerenauslese) and BA (Beerenauslese) wines of Germany. Other key wines to seek out include Bonnezeaux, Quarts de Chaume and Coteaux du Layon from France's Loire Valley, VT (Vendage Tardive) and SGN (Sélection de Grains Nobles) wines from Alsace, France,TBA and BA wines from Austria's Burgenland as well as examples from Australia and California.
Mary Gorman-McAdams, MW (Master of Wine), is a New York based wine educator, freelance writer and consultant. In 2012 she was honored as a Dame Chevalier de L'Ordre des Coteaux de Champagne
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