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Noble rot – exploring the oddly desirable fungus that shapes the world’s most luxuriously sweet wines

Emilee Tombs
June 21, 2024
7.5 min

In the enchanting world of wine, there exists a category of wine so rare and exquisite that it has earned its place in the most coveted cellars around the globe. For the discerning collector, wines affected by noble rot represent the pinnacle of a collection. Several summers ago, travelling through western France with my now-husband, we visited the town of Saint-Croix-du-Mont on the banks of the Garonne River near Bordeaux. The town is famous for its wall of fossilised oysters; said to lend an intriguing minerality to the white wines made in the region, but also for its sweet wines made using an even more intriguing fungus: noble rot.

We set off early and arrived in Sauternes around 11am. The morning mist hadn’t yet shifted and walking towards the vantage point overlooking vast plains of vines felt like parting a heavy curtain of water vapour. The fog, we came to learn, is an integral part of the winemaking landscape. In Bordeaux, Hungary and Germany, and it plays a major role in shaping some of the most expensive sweet wines in the world. 

Château d'Yquem

“Making sweet wine from Botrytis is taking huge risk for a winemaker,” says Laszló Mészáros, director at Disznókő, one of Hungary’s premier sweet wine producers. “You can't be sure that you achieve what you had expected. For noble rot to take place, the conditions in the vineyard have to be perfect; early morning mist to create the breeding ground for Botrytis cinerea – the fungus known as noble rot – and warm, dry afternoons to slows down the fungal process. These conditions stop Botrytis from turning into grey rot, which can ruin a crop. “When conditions are just right, Botrytis pierces the grape skins and the liquid inside the grape slowly evaporates. The grapes shrivel and the sugars, favours and acids concentrate. The resulting wines are incredibly complex and can age for 10, 20, 30 or more years. Noble rot is used in the production of the very best sweet wines in the world, including Sauternes from Bordeaux (the region south of Saint-Croix-du-Mont), Tokaji from Hungary, Beerenauslesen and Trockenbeerenauslesen (TBA for short) from Germany and Austria, and some late-harvest wines from Alsace and northern Italy. This unique phenomenon transforms healthy grapes into intensely sweet wines with incredible depth and complex flavours.

Situated in the foothills of the Carpathian Mountains, near the border with Ukraine and Slovakia, Tokaj in Hungary is the first delineated wine region in the world; established in 1737 by royal decree. Here, the conditions are ideal for making sweet wines from noble rot. The Bodrog and Tisza rivers help to necessitate the development of noble rot, resulting in wines that are incredibly sweet but with high levels of acidity and complex flavours. Aszú (meaning ‘shrivelled’) berries are picked individually by hand, with pickers going out in stages over a period of months to harvest. These berries are macerated with still wines and then categorized by puttonyos; indicators of how sweet the final wine will be. Five puttonyos describes a wine with a minimum of 120 grams per litre of residual sugar. Six puttonyos indicates a wine with 150g per litre. Below 5 puttonyos, and the wine can no longer be called Tokaji Aszú.

“This is a very expensive and labour-intensive process,” says Mészáros. “And this contributes to the rarity of the wines, and of course, their price.”

A 50cl bottle of 2015 Disznókõ Kapi, Tokaji Aszú 6 puttonyos, made from a single plot on the estate, currently retails at Berry Bros. & Rudd for around £170 without tax. This particular wine is only the fourth vintage from the estate, following on from the 1999, 2005 and 2011 vintages, which are difficult to get hold of. Made with Furmint and Hárslevelu grapes, these wines boast a wonderful golden colour when young, developing to amber with age. They are aromatic and packed with aromas of candied citrus peel notes, dried apricot, honey and ginger – flavours characteristic of noble rot – with a tangy well-balanced acidity.

While Tokaji Aszú is never cheap, it’s considered by many to be a canny purchase compared to Sauternes, the wine region I found myself in several years ago. Located to the southwest of Bordeaux, along the bank of the Garonne River, the region relies on the same misty mornings and warm, dry afternoons as in Tokaj. Sauternes wines are recognised in the infamous Bordeaux 1855 Classification with three cru classé ranks. Though only one chateau can claim the top Premier Cru Supérieur status, which is Chateaux d’Yquem. (There are many more, including Château Suduiraut which borders Yquem, that offers better value).

Château Suduiraut

Collectors often find that Sauternes wines from Château d'Yquem and Château Suduiraut reach their zenith after decades of aging, which is perhaps why you won’t find many on the market. Though of course, the very nature of these wines being made in small quantities due to lower, more concentrated yields also contributes to their rarity. The evolution of these wines in the bottle unveils layers of complexity and a perfect balance between sweetness and acidity. The wines may also develop more interesting tertiary flavour as they age, such as caramel, dried fruit and spice from oak. In Sauternes, the wines are made using relatively neutral-tasting but age-worthy Sémillon, a white grape which has a thin skin susceptible to noble rot – as blended with Muscadelle and Sauvignon, it adds exotic aromatics to the final wine.

Back in Tokaj, an even rarer sweet wine exists. Eszencia is a wine which has achieved near mythical status around the world. Created from the free-run juice of the raisoned Aszú grapes, it contains at least 450g per litre of residual sugar and the must (grape juice) is so sweet that it can takes years to ferment. The resulting wines are very low in alcohol – usually less than 5% – and are so lusciously sweet as to be compared to honey. Such wines are rarely sold outside of the Tokaj region, but The Ritz Hotel in London serves it by 10ml glass spoonful – as is traditional in Tokaj – for £35. Noble rot sweet wines are a treasure trove for any wine collection, and the world of Tokaji Aszú and Sauternes offers a myriad of choices for those seeking the pinnacle of this genre. Collectors who have had the privilege of exploring these wines know that they are more like works of art than wine. And, as with rare art, usually what sets these wines apart is the story behind them.

I’ve often thought back to our day exploring Sauternes and how it opened a new and exciting wine world for me. Once the fog had lifted, we took a stroll through the small village and stumbled into the garage of a winemaker offering tastings. It was a rudimentary operation with just two bottles of unlabelled wine on a trestle table alongside a bowl of walnuts alongside. One wine was the colour of honey, and the other was such as intense shade of amber that I half-expected to see a mosquito suspended in the middle of it. The winemaker – or perhaps farmer is a better description – didn’t speak English and only had two or three teeth, but his proposal was clear: “Try my wines. I think you’ll like them.”

These wines were unlike anything I had tried before; lusciously sweet with pranging acidity that made them insanely drinkable despite the level of sweetness. Flavours of dried apricot, canned peaches, honeysuckle, ginger, toast, marmalade, and baking spice; the calling cards of the noble rot fungus. “We call it called noble rot because it is a noble kind of rot,” says Mészáros. “Conditions like this don’t happen every year. And when they do, we count our lucky stars.”

The rarest of them all. The Ritz Hotel in London offers the change to taste history. Serving 10ml measures of Disznókő Eszencia by glass spoon as is traditional in the Tokaji region in Hungary, it’s an experience to be savoured. On October 14, 2004, Wine Spectator’s Peter D. Meltzer declared a 1847 Château Y’quem the “most expensive bottle of wine ever auctioned in the United States and the highest price ever realized for a bottle of white wine worldwide.”