What is passerillage (grape drying)?

If you've ever eaten a raisin and noticed how much sweeter it is than a fresh grape, you already understand the principle behind passerillage. But winemakers have turned this simple idea into an art form stretching back thousands of years.

After harvest, grapes are laid out on straw mats, wooden racks, or hung from rafters in well-ventilated rooms. Over weeks or months, water evaporates — sometimes losing 30-50% of the grape's weight — leaving behind concentrated sugars, acids, and flavour compounds.

The key is controlling the environment. Too humid, and you get unwanted mould. Too dry or hot, and the grapes turn into actual raisins (great for snacking, terrible for wine). Italian producers of Amarone use modern drying rooms (called *fruttaio*) with fans and climate control, keeping temperatures between 5-15 °C and humidity around 60-70%.

What's remarkable about Amarone is that despite using dried grapes loaded with sugar (350+ g/L), it's fermented to dryness — producing a powerful, full-bodied red at 15-17% alcohol. It's not sweet at all. France's Vin de Paille from the Jura, on the other hand, remains a luscious sweet wine with golden colour and notes of honey, dried apricot, and caramel.

Passerillage differs from noble rot (botrytis) in an important way: no fungus is involved. The concentration is purely physical — evaporation. This gives the wines a cleaner, more fruit-pure character compared to the honeyed complexity of botrytis-affected wines.