Botrytis Cinerea

Botrytis cinerea is a necrotrophic ascomycete fungus that infects a wide range of plants, including grapevines, strawberries, and many vegetables. In viticulture, it is famously described as a 'Jekyll and Hyde' organism: the same species causes devastating grey rot in wet conditions, yet produces noble rot when humidity alternates correctly with warmth and dryness. The fungus penetrates grape skins through stomata, wounds, or microfissures, breaking down cell walls and allowing water to evaporate. This dehydration concentrates sugars, acids, and aromatic compounds in the berry.

• Grey rot and noble rot are both caused by Botrytis cinerea; the outcome depends entirely on climatic conditions
• The fungus thrives at humidity above 80% and temperatures between approximately 12 and 25°C
• Botrytis colonization of grapes for noble rot purposes ideally occurs after veraison when berries are fully ripe
• White grape varieties such as Semillon, Riesling, and Furmint are particularly well suited to noble rot production due to thin skins and susceptibility to the fungus

Noble rot demands a very specific and repeatable climatic pattern: humid, misty mornings that allow fungal spores to germinate and penetrate grape skins, followed by warm, sunny, and breezy afternoons that slow the infection and encourage water evaporation rather than runaway rot. If high humidity persists throughout the day without drying, the infection accelerates into destructive grey rot. Proximity to rivers and lakes is the most reliable generator of these morning mists, which is why the world's classic noble rot regions are all located near significant bodies of water.

• Morning mists from rivers such as the Ciron in Sauternes and the Tisza and Bodrog in Tokaj generate the humidity needed for Botrytis spore germination
• Warm, breezy afternoons are critical to drying the vineyard and slowing fungal spread, keeping the infection within the berry rather than spreading destructively
• The botrytization process typically takes 10 to 20 days from initial infection to the pourri roti stage optimal for harvest
• Noble rot is unpredictable and vintage-dependent; in years without suitable conditions, many producers make dry white wines instead

Botrytized wines are defined by extraordinary concentration, viscosity, and aromatic complexity that sets them apart from all other naturally sweet wine styles. As the fungus dehydrates the berries, sugar levels rise dramatically while the fungus simultaneously triggers metabolic changes in the grape that generate novel aromatic compounds. Sotolon contributes honey and caramel notes, phenylacetaldehyde adds beeswax and honeyed character, and various lactones produce apricot and stone fruit aromas. Elevated glycerol from fungal activity creates the characteristic silky, viscous mouthfeel, while preserved acidity provides freshness and the potential for long aging.

• Residual sugar in botrytized wines frequently exceeds 100 g/L; Tokaji Eszencia, made from free-run juice of Aszú berries, typically contains over 450 g/L
• Botrytis consumes tartaric acid and converts it to gluconic acid and glycerol, altering the tartaric to malic acid ratio from 2:1 in healthy berries to approximately 1:3 in botrytized berries
• Stone fruit aromas such as apricot and peach are generated directly within the berry as a metabolic response to the fungal attack, while honey notes derive from the botrytis itself
• High acidity is preserved despite massive sugar concentration, preventing the wines from tasting cloying and providing the framework for decades of aging

A handful of regions around the world produce noble rot wines with reliable consistency, all sharing proximity to rivers or lakes that generate autumn morning mists. Sauternes in Bordeaux, built almost entirely around botrytized Semillon, Sauvignon Blanc, and Muscadelle, is the most internationally recognized. Tokaj in northeast Hungary, home to one of the earliest documented records of botrytized winemaking dating to at least the late 16th century, produces Tokaji Aszú from Furmint, Harslevelu, and other native varieties. Germany's Rhine and Mosel valleys produce Beerenauslese and Trockenbeerenauslese from botrytized Riesling, while Alsace produces Sélection de Grains Nobles from fully botrytized Riesling, Pinot Gris, Gewurztraminer, and Muscat. Austria's Burgenland region, near Lake Neusiedl, is also a consistent producer of world-class botrytized wines.

• Sauternes requires minimum 45 g/L residual sugar and a mandatory tasting exam to qualify for the appellation; its maximum yield is just 25 hL/ha, among the lowest in Bordeaux
• Tokaji Aszú regulations since 2013 set a minimum of 120 g/L residual sugar for all Aszú wines, replacing the former 3 to 6 puttonyos scale for most labeling purposes
• German Trockenbeerenauslese (TBA) is produced exclusively from individually selected botrytized or raisined berries and represents the highest Pradikat classification
• Alsace Sélection de Grains Nobles wines are made entirely from fully botrytized grapes and are produced only in exceptional vintages when conditions allow full noble rot development

Botrytized wines are among the longest-lived wines in the world. Their high residual sugar, preserved acidity, and the complex array of compounds produced during the botrytization process all contribute to remarkable longevity. Premium Sauternes from great vintages are noted for their potential to age well beyond 100 years, while Tokaji Eszencia, with its extraordinary sugar concentration above 450 g/L, can age for centuries. Over time, honey and fresh fruit notes evolve into more complex dried fruit, spice, and nutty tertiary characters, with color deepening from gold toward amber.

• Premium Sauternes from exceptional vintages are recognized as capable of aging well beyond 100 years in ideal cellar conditions
• Tokaji Aszú is required to be aged for a minimum of 18 months in oak under current regulations, with many top producers aging for considerably longer
• The combination of high sugar, high acidity, and botrytis-derived compounds provides the framework for long, graceful aging in bottle
• Color deepens progressively from gold to amber to deep copper as botrytized wines age, with some authorities suggesting deeper copper tones signal the beginning of mature, complex flavors