Can Grapes on the Vine Be Frozen?

Grape Development

• For the best grape flavor and lack of fungal diseases, the weather needs to be warm to hot and dry. Cool, rainy weather slows grapes' maturation and causes the fruits to be overly rich in water, and dilute in sugars and other flavor components. If the grapes are still immature with small size, hard skin and bitter flesh, a freeze in the vineyard effectively halts further maturation. The freeze kills foliage and fruit tissues.

Freeze Effects

• Freezing temperatures kill leaves and stem tissues that transport sugars made during photosynthesis into the developing grapes. Water present in the grapes freezes, expanding and cracking the grape skin. Once the grapes thaw, the flesh is exposed to air, disease spores and insects. Sweet juices drip out of the fruit's skin wounds. The damaged grapes rot and turn rancid in days.

Fruit Harvest Insight

• Immature grapes that freeze on the vine are not harvestable. The fruits do not sweeten or further develop. Grapes ready for harvest but were exposed to frost or freeze in the vineyard can be harvested, but it must be done quickly. Frozen grapes can shatter and skins break during harvest and being tossed and rolled around in buckets and trucks. To capture the grape's best flavor and juice quality, the grapes must be immediately crushed and pressed to obtain the juices and flavorful skins before decomposition advances. Frozen grapes cannot be used for shipment to markets for use as fresh table grapes.

Ice Wine

• Some grape growers dally in the difficult winemaking process yielding ice wine. Ice wine is made from ripe grapes deliberately left on the vine to fully freeze, then immediately picked and pressed. As the grapes freeze, the cold converts any remaining compounds remaining in the ripe fruits into sugars and acids. These frozen grapes are pressed and the juice fermented. In Germany, where it is called eiswein, Riesling grapes are frozen. In Canada, the world's largest producer of ice wine, the Vidal variety is commonly used.