So I was interested in attending a talk on the subject by Josh Rude who is winemaker at Wasson Brothers and Buddha Kat Wineries in Oregon’s Willamette Valley.
It turns out that cold soak, used mostly in red wine making, simply means keeping freshly picked grapes at a low temperature before fermentation.
Josh explained that after picking the grapes and removing their stems the grapes were crushed and then put into a fermenting tank. So far this is the standard process for making red wines. But instead of allowing fermentation to start as normal, the tank is cooled down to 40-45 degrees Fahrenheit (4.5—7 degrees Celsius). At this temperature fermentation doesn’t start and it is too cold for any micro-organisms to be active.
This is the cold soak and it can continue for some weeks.
The purpose of leaving the juice and skins together for a long period is that more colour and flavours are extracted from the skins, but without getting unwanted tannins.
The cold soak process continues until the winemaker decides that it has done its job. How long that will be depends on the grape varieties in the tank and the style of wine that is being made.
When the time is right the temperature is raised and the fermentation is allowed to start either naturally or, more commonly, by the addition of yeast. Fermentation extracts colour and tannins from the skins, but prior cold soaking is considered by its advocates to add extra layers of flavour and more complexity in the finished wine.
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Peter F May is the author of Marilyn Merlot and the Naked Grape: Odd Wines from Around the World which features more than 100 wine labels and the stories behind them, and PINOTAGE: Behind the Legends of South Africa’s Own Wine which tells the story behind the Pinotage wine and grape, also available for the Kindle.
Disclosure: Josh Rude was speaking at the American Wine Society Annual Confernce in Portland Oregon. The author travelled to the Conference at his own expense, and as a conference speaker had free entry to this seminar.