Icewine Fermentation

Dear Colleagues,

Icewine (also known as eiswein) is a sweet dessert wine made from grapes that have naturally frozen on the vine. During pressing, water in the frozen berries is retained as ice, so the resulting juice is twice as concentrated in sugars, salts, acids, and flavour compounds. These concentrated solutes place fermenting yeast under increased hyperosmotic stress, leading to reduced cell growth and altered metabolism that can impact the organoleptic profile of the wines. With changes in climatic conditions due to global warming, the windows of opportunity to harvest icewine grapes while the berries remain frozen (below -8°C in Canada; below -7°C in Germany) are becoming increasingly fewer, which could add to the rarity of icewine in the international marketplace.

Overcoming fermentation challenges is being addressed not only through winemaking techniques, yeast conditioning, and nutrient and micronutrient additives, but also through yeast selections. Non-Saccharomyces cerevisiae yeast like Torulaspora delbrueckii used in combination with Saccharomyces cerevisiae yeast is among the combinations trialed for icewine production. These options have proven successful in not only reducing volatile acidity in wine but also in further enhancing the aroma and flavor profile of icewines. New yeast isolates, alone or in combination with S. cerevisiae, and the impact on the volatile organic compounds in wine could lead to new styles of icewine for the marketplace.

Icewines are typically made from Vidal, Riesling, or Cabernet franc, and each grape variety poses different challenges to yeast during fermentation due to the varied juice composition from each grape variety. A further understanding of the stress responses of wine yeast during the course of fermentation from the initial hyperosmotic stress from juice solutes to the ongoing adaptation as sugar concentrations reduce and ethanol concentrations increase will further improve our understanding of how yeast responses impact icewine quality.

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• icewine
• dessert wines
• hyperosmotic stress
• non-Saccharomyces and Saccharomyces yeast during fermentation
• reduced yeast growth
• controlling volatile acidity
• wine quality
• wine yeast adaptation