Like most things in wine, cold-soaking — a technique used to extract flavors and aromas while minimizing harsh tannins — is the subject of contemporary debate. While some winemakers feel it is an invaluable way to develop desirable flavors, others say it’s both inefficient and ineffective.
The origins of cold-soaking are a bit murky, but one generally accepted history suggests the practice rose to prominence in Burgundy in the 1970s. As the story goes, cold temperatures around harvest time meant wines naturally cold-soaked: In the era before temperature-controlled wineries and stainless steel tanks, if it was cold outside the winery, it was cold inside the winery and the tanks. As a result, fermentation often took several days.
Today, the commonly cited rationale for cold-soaking grapes is to deepen the color while avoiding over-extracting tannins. The two are closely connected, as pigment molecules, known as anthocyanins, commonly bond with tannins during the maceration process.
“The standard thinking is that the cold-soak period favors anthocyanin extraction as opposed to alcoholic extraction, which favors tannin extraction,” David Ramey, winemaker, Ramey Wine Cellars, says. And so winemakers in regions that produce tannic reds like Cabernet Sauvignon, such as much of California and Australia, often favor cold-soaking.
Now, however, as we learn more about the complex science of winemaking, there’s some skepticism about the actual advantages of the practice. Dr. James Harbertson, Associate Professor of Enology at Washington State University and an expert on tannins, believes that “the benefits are really about aroma.”
“The origins of cold-soaking are actually from white wine production,” he says. “In white wine production you’re attempting to get a bit of flavor from the skins, which is carried to an extreme in orange wine production. The danger for white wine production is you pick up phenolics, bitterness, and oxidation with more skin contact, but the benefit is more aroma.”
That might help explain why Pinot Noir was the initial red grape to receive the cold-soak treatment; in many ways Pinot Noir is closer to a white grape than a red grape, it’s naturally low in pigment and is defined more by aroma than color, all characteristics that cold-soaking would help to enhance.
Instead of just relying on temperature-controlled tanks or wineries, producers like Ramey are starting to experiment with using dry ice, or frozen carbon dioxide, as the means of cooling down their grapes. “We’re in our second year of experimenting with dry ice,” Ramey says. “It has several effects: It cools the must quickly, it tends to exclude oxygen, which I’m opposed to in white juice but not opposed to in red juice, and when you’re sprinkling dry ice onto the berries, the carbon dioxide ruptures some of the grape skin cells and facilitates the release of pigment into the juice.”
Harbertson is dubious that cold-soaking is useful in most cases. “The story that’s told is that you get pigment without tannin, but the reality is that anthocyanins are water-soluble and are super easy to extract,” he says. “Thin-skinned grapes like Pinot Noir and Grenache are outliers, but for something like Cabernet Sauvignon, you don’t need to do it.”
This is an important point because cold-soaking is not without its risks and costs. One primary concern is the heightened chance of spoilage.
“Several strains of wild yeast that can produce funky and unpleasant aromas live on the outside of the grape, and they can tolerate colder temps and small amounts of sulfur dioxide,” Harbertson says. “It takes a lot of electricity to cold-soak, or you can use dry ice, which is just a greenhouse gas turned solid, but no matter what, it will cost you time, money, or something.”
With the allure of deep color and silky tannins still going strong, it’s an investment many winemakers continue to make. For now.