Botrytis explained

Despite being a common enemy in a range of fruit and vegetables, an alignment of stars results in this particular strand of grey rot being responsible for some of the world’s most opulent, expensive and desired dessert wines, such as the sélection de grains nobles of Alsace, Germany’s sweeter styles, Sauternes in Bordeaux, and Tokaji in Hungary, where it is argued botrytised wines were first made.

Right place, right time

Botrytis is a permanent resident in most vineyards throughout the year, which makes it an ongoing threat. Towards the end of the ripening season, however, in the right settings, it transforms from unwelcome visitor to VIP.

The base ingredient for botrytis is the presence of water in the form of lakes or rivers. These create misty, humid mornings that trigger the rot’s bloom. As the botrytis spores cloak the berries they attack the skin and exploit microscopic fissures to cause punctures.

Should damp conditions persist, then the berry would naturally degrade and ruin. However, those regions whose reputations are built on botrytis-crafted wines rely on an ace up their sleeve, namely their warm, sunny and dry afternoons. Not only does this maintain ripening, but it also halts the spread of the rot and causes water in the grapes to evaporate out through the pierced skin, leading to the concentration of sugars, flavours and aromas within the berry.

Botrytis also infuses the grapes with its own set of aromatic compounds, often slightly medicinal – these can include honey, marmalade, ginger and beeswax.

Expertly crafted

Arbitrary in nature, noble rot doesn’t work uniformly but spreads, berry by berry, at varying pace. Therefore, for those producers with the financial means to do so, several rounds of handpicking are required, with these multiple passes through the vineyard capturing only grapes that are perfectly affected by the rot. Unsurprisingly, yields are extremely low, even tiny, not only due to the hand-harvesting of grapes at their optimum, but also to the vastly reduced volume of liquid inside them. In the winery, the grapes are handled with kid gloves, and pressing is carried out slowly and carefully, or – in the case of Tokaji – while being macerated with fermenting juice or a youthful base wine.

Drawn-out fermentations are the norm and require a beady eye in order to stave off a host of threats, not least refermentation, which can be triggered by the high sugar levels at play.

Botrytis: In the glass

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