Many of the world’s best dessert wines (and few of the ones we tried the other night) are made by botrytis effected grapes.  We talked a little bit about it at the tasting, but if you were unfortunate enough to not have been at our past dessert wine tastings or didn’t get the full story, here’s the skinny on how these amazing wines are made.

All about the ‘Noble Rot’ – Botrytis 

Botrytis cineria is fungus that can grow on many types of fruit and produce given the right conditions.  For most farmers and growers, these conditions are dreaded unless you are trying to make a dessert wine.  Moist, damp and conditions can cause the mold to form on grape clusters.  When conditions remain wet cool for too long, the fungus will progress to the point where it ruins the grapes and is known as grey rot.  When warmer and drier weather follow the damp conditions that cause the the onset of the fungus, it is kept in check and develops into what dessert wine producers pray for – “Noble Rot.”

Grapes that have been attacked by the Noble Rot fungus are responsible for many of the world’s most famous dessert wines – Sauternes, Tokaji, Trokenbeerenausle, Australian Stickies…

So how do rotten grapes ending up making wines so delicious and sweet?  The fungus does two things to the grapes.

1) When spores of the botrytis fungus land on grape berries germinate, they grow filaments, whose tips exude an enzyme that dissolves tiny holes in the berry’s skin and allows the filaments to work their way inside. Once inside the berry, the filaments cover the skins and make millions of spores. More than half the water inside each berry is lost to the rot, and as the berries shrink, the sugar inside doubles in concentration. The rot metabolises the acids, along with a bit of the sugar. The result is very sweet juice that retains vibrant acidity.

2) As the grape begin to dehydrate and rot, botrytis digests its sugar and acid, and excretes glycerol, which contributes to the silky mouthfeel of the wines. It also injects an enzyme – laccase – into the berries, that turns the juice a lovely golden colour, and reacts with tannins and other phenolics to reduce bitterness and astringency.  Laccase is also an oxidising enzyme, and as the sugars oxidise, they produce a stunning range of honey, apricot,
and caramel flavors.We all know that molds and fungi do some great things to cheeses and in making medicines (think penicillin), but who knew it could do such great and complex things to a wine grape?