Botrytis / Noble Rot

(See also: Auslese, Beerenauslese / BA, Prädikatswein / QmP,Trockenbeerenauslese / TBA)

How could rotten grapes be good for wine, let alone noble? When the fungus Botrytis cinerea grows on ripe grapes under favorable weather conditions it results in noble rot, so-called because the wines made from such grapes are the most sought after sweet wines in the world. Botrytis punctures the grape’s skin to get at the sugar and tartaric acid in the juice upon which it then feeds. The water in the grapes then evaporates through the hundreds or thousands of holes in the skin of each berry, thereby concentrating the juice. Depending upon the weather conditions the fungus growing on the grapes can look like fuzz or the grapes can end up looking like dry raisins. The fungus exudes an enzyme (laccase) that oxidizes a whole slew of aromatic and other substances in the skins of the berries and this process also causes the grapes to change color.

When affected by Botrytis the Riesling grapes at Gut Hermannsberg turn first from golden to pale violet, then brown. Parallel to this their taste changes, first become like an exotic fruit coulis (Auslese), then like dried yellow fruits with floral honey (Beerenauslese /BA) and finally dried dates and figs with forest honey and dried spices (Trockenbeerenauslese /TBA). These and other positive effects upon the wine can easily be compromised if other fungi grow alongside Botrytis or replace it on the grapes. Likewise, if Botrytis starts growing on the grapes before they are properly ripe or if the weather is too wet for them to shrivel, then the result doesn’t taste very noble.

That’s why Gut Hermannsberg does not produce wines of this kind very often (the last vintage was in 2015).