Noble rot

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Noble rot on Riesling grapes (Rheingau, Germany, 2005) Botrytis riesling.jpg
Noble rot on Riesling grapes (Rheingau, Germany, 2005)

Noble rot (French : pourriture noble; ‹See Tfd› German : Edelfäule; Italian : Muffa nobile; Hungarian : Aszúsodás) is the beneficial form of a grey fungus, Botrytis cinerea , affecting wine grapes. [1] Infestation by Botrytis requires warm and humid conditions, typically around 20 degrees celcius and above 80% humidity. [2] If the weather stays wet, the undesirable form, "bunch rot" or "grey rot", adversely affects winemaking by disrupting fermentation and changing the taste, aroma, and appearance of the final wine [1] [2] [3] Grapes typically become infected with Botrytis when they are ripe. If they are then exposed to drier conditions and become partially raisined, this form of infection is known as noble rot. Grapes picked at a certain point during infestation can produce particularly fine and concentrated sweet wine. Wines produced by this method are known as botrytized wines, [4] and are considered a distinct category of dessert wines. [3]

Contents

The primary distinction between botrytized wines and other naturally sweet, non-fortified sweet wines, such as late-harvest wines, ice wines, or straw / raisin wines, lies in the range and richness of aroma compounds generated by the Botrytis cinerea fungal infection of the grapes. [3] Significant differences are also evident in other components, like sugar alcohol and acid composition, due to microbial activity. [3] Descriptors frequently used for these wines highlight flavours of peach, apricot, pear, quince, raisin, and honey, along with unique "botrytis" or roti characteristics. [3] [5] Additionally, a notable feature of botrytized wines is their high acid content, which prevents them from tasting cloying, even with sugar levels often exceeding 200 g/l [3]

Effect on grapes

When Botrytis cinerea infects grapes, it initiates several physiological changes that are crucial for the development of noble rot wines. The fungus penetrates the grape skins while feeding on the grapes, causing microscopic wounds that lead to the evaporation of water from the berries. [5] This dehydration process concentrates the remaining sugars, acids, and flavour compounds within the grapes, resulting in a higher density of these essential components. The weight of the grapes can decrease by up to 60%, leaving behind a shrivelled, sugar-rich berry. [2]

The infection also significantly alters the chemical composition of the grapes with the concentration of sugars in the grape increasing dramatically. This high sugar content is essential for the production of the sweet wines associated with noble rot. [2] The fungus primarily consumes tartaric acid, which is more prevalent than malic or citric acid in healthy grapes, with remaining tartaric acid transformed into gluconic acid and glycerol. [5] During the infection process, the ratio of tartaric to malic acid changes, as observed in Furmint grapes used for Tokaji Aszú, where the ratio shifts from 2:1 in healthy berries to 1:3 in botrytised berries. The increased levels of citric acid and the formation of higher levels of sugar alcohols (such as glycerol, arabitol, mannitol, sorbitol, and inositol) by the fungus contribute to the complexity and mouthfeel of botrytized wines. [1] [2] The grapes metabolic stress response also leads to the production and concentration of various aromatic compounds. The berries concentrate precursors for citrus aromas like lemon and grapefruit, and also generate compounds for stone fruit aromas such as apricot and peach in a direct metabolic response to the fungal attack. Some of these aromatic characteristics, including the distinct honey aroma, are directly attributable to the botrytis fungus itself. [1] [2]

The stress response of grapes to botrytis infection is similar to their response to drought. The breakdown of grape skin cells by the fungus facilitates water evaporation, intensifying the dehydration process. This stress response allows the grapes to adapt metabolically, slowing down the infection rate compared to grey rot, which spreads too quickly for the plant to respond effectively. [2]

Origins

According to Hungarian legend, the first aszú (a wine using botrytised grapes) was made by Laczkó Máté Szepsi in 1630. However, mention of wine made from botrytised grapes appears before this in the Nomenklatura of Fabricius Balázs Sziksai, which was completed in 1576. A recently discovered inventory of aszú predates this reference by five years. When vineyard classification began in 1730 in the Tokaj region, one of the gradings given to the various terroirs centered on their potential to develop Botrytis cinerea.

There is a popular story that the practice originated independently in Germany in 1775, where the Riesling producers at Schloss Johannisberg (Geisenheim, in the Rheingau region) traditionally awaited the say-so of the estate owner, Heinrich von Bibra, Bishop of Fulda, before cutting their grapes. In this year (so the legend goes), the abbey messenger was robbed en route to delivering the order to harvest and the cutting was delayed for three weeks, time enough for the botrytis to take hold. The grapes were presumed worthless and given to local peasants, [6] who produced a surprisingly good, sweet wine which subsequently became known as Spätlese , or late harvest wine. In the following few years, several different classes of increasing must weight were introduced, and the original Spätlese was further elaborated, first into Auslese in 1787 [7] and later Eiswein in 1858 (although Eiswein is usually made from grapes not affected by Botrytis). [8]

Viticulture and uses

Botrytis cinerea on Semillon grapes in Sauternes SemillonBotrytisCinerea.JPG
Botrytis cinerea on Semillon grapes in Sauternes

In some cases, inoculation occurs when spores of the fungus are sprayed over the grapes, while some vineyards depend on natural inoculation from spores present in the environment.

The fungus perforates the grapes' skin, allowing water in the grape to evaporate during dry conditions, and thereby raising the sugar concentration in the remaining juice.

Some of the finest botrytized wines are picked berry by berry in successive tris (French for "selections").

Internationally renowned botrytized wines include the aszú of Tokaj-Hegyalja in Hungary (commonly called Tokaji or Tokay), [5] Sauternes from France [5] – where the process is known as pourriture or pourriture noble, and Beerenauslese or Trockenbeerenauslese wines from Germany and Austria. [5] Other wines of this type include the Romanian Grasă de Cotnari, French Coteaux du Layon, French Monbazillac, Austrian Ausbruch, [5] South African Noble Late Harvest (NLH) and Croatian Wine maker Vinarija Mihalj from Kutjevo (producing Mačevo brdo-Graševina). Depending on conditions, the grapes may be only minimally botrytized. Botrytized wines are also produced by Californian, and Australian winemakers. [5]

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<span class="mw-page-title-main">Riesling</span> White grape variety

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<span class="mw-page-title-main">Tokaji</span> Hungarian and Slovakian variety of wine

Tokaji or Tokay is the name of the wines from the Tokaj wine region in Hungary or the adjoining Tokaj wine region in Slovakia. This region is noted for its sweet wines made from grapes affected by noble rot, a style of wine which has a long history in this region. The "nectar" coming from the grapes of Tokaj is also mentioned in the national anthem of Hungary.

<i>Botrytis cinerea</i> Species of fungus

Botrytis cinerea is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" or "gray mold".

<span class="mw-page-title-main">Late harvest wine</span> Variety of wine

Late harvest wine is wine made from grapes left on the vine longer than usual. Late harvest is usually an indication of a sweet dessert wine, such as late harvest Riesling. Late harvest grapes are often more similar to raisins, but have been naturally dehydrated while on the vine.

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Trockenbeerenauslese, or TBA, is a German or Austrian botrytized wine made entirely from the individually selected grapes fully "dried" from Botrytis cinerea, hence the name. Trockenbeerenauslese is a very sweet wine, highest among the wines of the QmP category that includes also Auslese and Beerenauslese.

<i>Spätlese</i> German late harvest wine

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<i>Auslese</i> German wine category

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Sauternes is a French sweet wine from the region of the same name in the Graves section in Bordeaux. Sauternes wine is made from Sémillon, sauvignon blanc, and muscadelle grapes that have been affected by Botrytis cinerea, also known as noble rot. This causes the grapes to become partially raisined, resulting in concentrated and distinctively flavored wines. Due to its climate, Sauternes is one of the few wine regions where infection with noble rot is a frequent occurrence. Even so, production is a hit-or-miss proposition, with widely varying harvests from vintage to vintage. Wines from Sauternes, especially the Premier Cru Supérieur estate Château d'Yquem, can be very expensive, largely due to the very high cost of production. Barsac lies within Sauternes and is entitled to use either name. Somewhat similar but less expensive and typically less-distinguished wines are produced in the neighboring regions of Monbazillac, Cérons, Loupiac and Cadillac. In the United States, there is a semi-generic label for sweet white dessert wines known as sauterne without the "s" at the end and uncapitalized.

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References

  1. 1 2 3 4 Blanco-Ulate, B.; Amrine, K.; Collins, T. (December 2015). "Developmental and Metabolic Plasticity of White-Skinned Grape Berries in Response to Botrytis cinerea during Noble Rot". Plant Physiology. 169 (4): 2422–2443. Bibcode:1985QuRes..23...87O. doi:10.1104/pp.15.00852. hdl: 11336/10951 . PMC   4677888 . PMID   26450706.
  2. 1 2 3 4 5 6 7 Clarke, Jim (4 September 2023). "The Science Behind Noble Rot Wines". SevenFiftyDaily. Retrieved 30 June 2024.
  3. 1 2 3 4 5 6 Magyar, I. (2011). "Chapter 6 - Botrytized Wines". Advances in Food and Nutrition Research. 63: 147–206. doi:10.1016/B978-0-12-384927-4.00006-3. ISBN   978-0-12-384927-4. PMID   21867895.
  4. ↑ Labensky, Steven (1997). Webster's new world dictionary of culinary arts. Prentice-Hall. p.  28. ISBN   9780134757322.
  5. 1 2 3 4 5 6 7 8 "Botrytis Cinerea: The Noble Rot". vinoble.org. 4 September 2023. Retrieved 13 July 2024.
  6. ↑ A Short History of Riesling
  7. ↑ Karen MacNeil The Wine Bible Workman Publishing 2001 page 540 ISBN   1-56305-434-5
  8. ↑ "A History of Schloss Johannisberg". Archived from the original on 2012-03-04. Retrieved 2010-03-25.
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