When a major blizzard hammered the Midwest in early February, my thoughts turned not only to my family in Michigan, but to the wines that would also be subjected to those freezing temperatures.
Here in California, extreme heat is a major concern during the summer months, but we rarely need to worry about our wines getting too cold.
But what if you live in a cold-climate region and your wine is forced to spend the afternoon in a shipping box on your front porch -- it’s not legal for the shipper to leave it there, but it happens -- or in the trunk of your car during a winter storm? And who among us has never popped a bottle into the freezer for a quick chill-down, only to forget about it for a few hours, or even overnight? (Guilty as charged, Your Honor.)
I know all too well that wine can turn into a Slushee if left in the freezer too long, but what are the scientific effects on the wine? Does exposure to the cold change its character?
I checked in with Dr. Christian Butzke, enology professor and associate professor of food science at Purdue University in Indiana. Several years ago, Butzke studied the effects of temperature extremes on wine while working on a project with Robert Mondavi Winery and Delicato Vineyards.
“There are a number of issues that relate to increased headspace pressure and ethanol (alcohol) concentration due to partial freezing,” he told me. “These in turn impact closure integrity -- for example, leakage/seepage, air influx -- as well as tartrate stability, protein stability, and possibly mouthfeel.”
When exposed to freezing temperatures, the water in wine begins to freeze, and thus expands -- which can force the cork out of the bottle, along with some of the wine. This can lead to issues like oxidation when the wine warms, contracting and pulling air into the bottle as it does so.
Freezing can also initiate physical changes, like the formation of tartrate crystals (those tiny “diamonds” you sometimes find on corks). That’s not such a big deal for still wines, but it can cause problems in bubbly ones.
Sparkling wines are especially vulnerable to tartrate formation, Butzke explained, because the crystals cause the release of CO2 (carbon dioxide) when the bottle is opened, making the wine shoot out. If you’ve ever stuck Mentos candies into a 3-liter bottle of Diet Coke to watch the resulting geyser, the effect might look familiar. While this is fun when it’s happening with soda, you might not be so happy to see your precious Champagne dripping from the ceiling.
The increase in volume/pressure when sparkling wine freezes can also cause the bottle to break, resulting in a different kind of mess.
I should point out here that it’s not easy to make wine freeze solid. Water freezes at 32°F, and wine is mostly water. But the alcohol in wine lowers the freezing point -- the more alcohol it has, the lower the freezing point will be -- to around 22°F. (That’s why you can leave a bottle of vodka in the freezer for months and it will remain in liquid form.) Although the average freezer temperature is around 5°F, the wine will usually turn into an icy slush, rather than a wine-cicle.
Scientific theory is all very interesting, but how does this play out in the real world?
Butzke suggested that a carefully organized comparative tasting of previously frozen wines vs. non-frozen wines would be an interesting exercise, so I decided to try it -- obviously on a much smaller scale than Butzke and his colleagues at Perdue could pull off.
I headed to Trader Joe’s and picked up two bottles each of three different wines: one white with a screwcap closure (a Rhone Valley blend), one white with a cork closure (a California table wine of unspecified grapes), and one red with a cork closure (a Pinot Noir from France). I stuck one bottle of each wine in the freezer and left the wines there overnight.
By the next morning, the wines were mostly frozen, each with a little bit of liquid still moving between blocks of ice and slush. Aside from being chunky, the whites looked fine, but the red didn’t fare so well -- red slush was crusted on the bottle neck, and the cork had started pushing its way out.
I placed the frozen whites in the refrigerator to join my “control” whites, and set the red on the counter to thaw. The following day, when all of the wines were ice-free, I set up my blind tasting.
There was an obvious difference in the screwcap-sealed whites. The previously frozen wine's aroma was very muted compared to the control wine, and it tasted watered down, like a few ice cubes had been left to melt inside the glass.
Next I tasted the cork-sealed whites, and found no discernable differences in aroma or flavor. The previously frozen red seemed to have less oak character than the control version, and I actually kind of preferred the freezer wine.
So what did I discover through my experiment? While my results were mixed, I learned that extreme cold really can have an effect on wine, from subtle to dramatic.
I also learned that more extensive research is needed in order to determine the specific effects of freezing temperatures on different types of wine, sealed under different closures, over time. (My cork-sealed white didn’t seem altered after 24 hours, but what would have happened if I’d waited a week to do the tasting? Are whites more vulnerable than reds?)
To find the answers to such questions, it will take a real scientist to handle the research. Dr. Butzke said he’d be happy to do the honors for the low-low price of a Purdue grad student research sponsorship: “Just three easy payments of $19,000,” he said.
In the meantime, there are steps you take to protect your wine from the cold.
Avoid ordering bottles to be shipped to your house during freezing spells unless you can be sure it’s being transported in heated trucks. Have your wine packages delivered to your office instead of your house, so the box doesn’t end up sitting around in a freezing cold warehouse for hours.
If you really need to chill a bottle in a hurry, an ice bath is quicker than the freezer, and even if you forget about it and leave it in the ice bucket for hours, you won’t end up with a busted bottle or a wine Slushee.