How do you hedge that?

No, I have not taken up answering horticultural queries.  This was a question posed by a merchant banker recently when I explained the risks involved in making great dessert wines such as Sauternes.

Wine growers in Sauternes, Tokaji in Hungary, Bonnezeaux and Vouvray in the Loire Valley, or indeed anywhere where the sweet wines depend on the development of botrytis cinerea (or noble rot) in order to attain their signature intensity and complexity, have an anxious time of it each harvest time.  Ideal conditions for noble rot combine morning mist with warm, sunny afternoons in the weeks leading up to harvest.

Filaments of botrytis cinerea fungus pierce thin-skinned grapes, such as Semillon and Chenin Blanc, resulting in loss of moisture from inside the grape, thereby increasing the concentration of sugar and acids, relative to the water content – but the same is true for grapes left to shrivel on the vine.  What makes noble rot so special is that it also leads to chemical changes within the grape which, rather than spoiling the flavour and making it taste mouldy, lead to the development of an array of additional flavours ranging from barley sugar to marmalade.     

In order for the beneficial effects to happen, botrytis cinerea  needs to affect ripe, healthy grapes.  Unripe or damaged grapes will go on instead to develop regular bunch rot, which will only spoil, rather than enhance flavours.  And healthy grapes can also be affected by bunch rot, rather than the noble kind.  While a small percentage of rotten berries in white wine will not affect the flavour (as I witnessed this September in Muscadet), because the grapes are immediately pressed and only the juice is fermented.  Any amount of rot (noble or not) in red wine can spell disaster for the wine, as the entire berry, mouldy skin and all, is required in the fermentation tank and the resulting wine is at risk of developing off-flavours and being undrinkable.

Almost as bad as the wrong kind of rot, is no noble rot.  Winemakers cannot legislate for noble rot and are subject to the weather delivering the goods at the right time in the ripening cycle.  If it doesn’t arrive in the vines, producers can make a late harvest dessert wine, or demi-sec style wine, but these will never have the complexity and age-worthiness of nobly rotten wines.

So, the right kind of rot pitches up at the right time, now you need to pick the grapes – sometimes individual bunches, sometimes individual berries affected by rot are picked.  Either way, several pickings or “tries” are needed to gather the grapes, adding to the expense of the process.

Since the grapes will have lost a great deal of moisture, yields will be incredibly low.  Whereas a grape vine might produce a single bottle of good quality dry wine (or perhaps 2-3 bottles of mass market wine), it will produce just a single glass of highly concentrated dessert wine. 

Finally, the winemaking is hardly a doddle.  Imagine trying to extract juice from a raisin and you begin to see the difficulty in pressing nobly rotten grapes.  The small amount of resulting juice is so high in sugar that fermentation is slow and can stop readily – a problem known as stuck fermentation.

Given all the trouble that goes into making them (if they can be made at all), these wines are really woefully underpriced and underappreciated.  It’s a wonder anyone carries on doing it – how do you hedge that indeed?  Perhaps the only logical answer is, "By having already made a fortune as a merchant banker."

When everything goes right – some recommended wines where botrytis plays a part:

The FMC Chenin Blanc 2011 - £24.50 from Great Western Wine, also available via independent merchants

This is not a dessert wine, but late harvesting of the grapes and inclusion of some botrytised Chenin Blanc berries makes for a rich, complex, off-dry style of wine.  Fermented using natural yeasts in new French oak barrels and left on the lees for 12 months, this has flavours of apple, quince, a hint of honey and hay that begins with a rich hit of ripe fruit, but finishes clean with piercing acidity.

Château Climens

2013 is unlikely to go down as a great vintage for red Bordeaux wines, but their loss could be Sauternes’ gain.  The warm and humid weather which arrived in late September provided ideal conditions for the rapid spread of botrytis, inimical to red wine quality and forcing many growers to pick red grapes earlier than they would have liked.  But it’s an ill wind that blows nobody any good and makers of sweet wines in the region were treated to an early and rapid spread of noble rot among their vines.  2013 could be a Sauternes vintage to watch out for when it arrives on the market in a couple of years’ time.

If money were no object Château d’Yquem would be my everyday Sauternes.  However, back in the real world, my favourite Sauternes is Château Climens – technically it’s from Barsac, the region adjoining Sauternes, but growers there are entitled to use the better known name of Sauternes.  Owner Bérénice Lurton manages to produce wines that are intensely sweet, yet beautifully drinkable, with elegant, smoky complexity.  While you wait for the 2013 to arrive, you can pick up a half bottle of the 2010 for around £70.

Château de Fesles Bonnezeaux 2010

Fesles is one of the most highly regarded producers in Bonnezeaux,  in the Anjou region of the Loire.  Early morning mist rising from the Layon river in late summer can create the ideal conditions for the development of noble rot, as it did here in 2010.  This is lusciously sweet with huge concentration and a feeling of stoniness as well as flavours of stone fruit.  It will age beautifully.  This vintage seems to be hard to find in the UK, but other botrytis vintages can be found, including the 1999, £26.96 for a 50cl bottle from Vintner’s Selection.  About half the grapes were affected by botrytis, the rest were late harvest, shrivelled berries.  It has a heady nose of honey, toast and quince, with luscious baked fruit on the palate.