Concentrating
When fermenting grape juice is too sweet, yeasts can’t convert all the sugar into alcohol, leaving behind residual sugar.
The Method: Botrytis
The Wines: Sauternes, Barsac, Tokaji, Ausbruch, Bonnezeaux, Quarts de Chaume, Coteaux de Layon, Sélection des Grains Nobles, Beerenauslese, Trockenbeerenauslese
How it Works: Botrytis cinerea is a fungus. In wet conditions, it destroys grapes, but when the grapes are ripe and the temperature and humidity are just right, it becomes the so-called “noble rot” pulling moisture out of the grape, leaving behind a shriveled berry with ultraconcentrated sugars, acids and flavors.
The Method: Drying on the Vine
The Wines: Jurançon, Cordon-Cut Australian Riesling
How it Works: Some grapes dry out on the vine, a process known as passerillage. Sometimes, growers help the process along by twisting grape clusters to cut off sap flow, or by slashing vine branches.
The Method: Late Harvest
The Wines: Spätlese, Auslese, Vendange Tardive
How it Works: The juice of late-harvested, ripe grapes are packed with sugar, and can be affected by passerillage or botrytis.
The Method: Drying on Racks
The Wines: Amarone, Vin Santo, Recioto, Pedro Ximénez, Passito
How it Works: Ripe grapes are harvested and then partially dried in the sun or air, causing water loss. In Italy, grapes are dried in well-ventilated lodges and lofts, a process known as apassimento. In Spain, Pedro Ximénez grapes are dried in the sun on esparto-grass mats to make PX wines that taste just like dark raisins.
The Method: Freezing
The Wines: Eiswein, Icewine
How it Works:Â Frozen-solid grapes are harvested and pressed immediately, making it easier to separate the frozen water from the rich, concentrated juice. Of course, modern freezers units can mimic the process.