Among the legions of dark mysteries standing between your lips and the enjoyment of a fine bottle of wine is learning to serve the wine at just the right temperature.
Unfortunately, the "proper" temperature is always colder than an invitingly warm dining room. So the wine must be chilled.
If you don't own a wine cellar, chances are you plan on cooling down a recently purchased bottle- a bottle that procrastinated in a warm car on its long way home from the liquor store. There is never enough time to prepare dinner, so a fast cooling method is imperative.
Now the most effective cooling method is direct contact with a cold liquid- plunge the bottle into a bucket of ice (or even better, salted ice which drops the temperature another 20F), and the wine cools in just a few minutes.
Yet a bucket of salty water can be a mess. Sometime the label even slides off in the process- nothing like serving your guests an anonymous vintage. So you might be tempted to place the bottle in the freezer for a quick, dry cool-down.
The problem is air is a much poorer thermal conductor than water- between 25 to 100 times worst. You don't need to be a scientist to realize if you place you hand in ice water it hurts immediately- but your fingers are only slightly discomforted poking around in the freezer.
Is there anything we can do to speed up the cooling process in air?
Two possibilities suggest themselves. First, you could place the bottle on a wet towel, so heat conducts from the wine, through the towel and then directly into the cold shelving. Or, you might wrap the bottle in a moist towel, hoping water evaporation will cool the wine (the freezer is drier than the warmest desert, so evaporation is potentially very effective).
So let's try a few tests. The first is modeled on a suggestion made by Cook's Illustrated. I wrapped a 750 ml wine bottle in a moist towel1, and drilled a hole through the cork so I could insert a thermocouple into the dead-center of the bottle. This bottle was placed on a shelf in a freezer, next to a bottle with an identical thermocouple but lacking a moist towel.
Note the bottle's orientation matters. A horizontal bottle will cool faster than a vertical bottle, because convection currents are stronger when the convection cells do not have to travel the long distance from the bottom of the bottle to the top of the neck. So all these experiments are with a horizontal orientation.
Here are the results. Assuming a proper serving temperature around 50F, there is hardly any difference at all between the two bottles, but even over the course of an hour, the moist towel wrapped bottle took LONGER to cool than the dry bottle.
Why longer? Well, its true the moist towel potentially could improve thermal conduction to the shelf compared to air. But, the towel is not really a great thermal conductor- between the cotton, entrapped air bubbles and the added mass which must also be cooled down, it's more of an impediment than an accelerator.
To see why, I froze three 1 L water bottles (it too painful to freeze another perfectly good bottle of wine, and in any case, the thinner plastic bottle eliminates the slower thermal path of a thick wine bottle glass wall). One bottle was plain, one tightly wrapped with a SINGLE dry paper towel, and one wrapped with a dry cloth towel:
Again note the plain, unadulterated bottle cooled fastest3. Even a single paper towels traps enough air to be a pretty effective insulator, almost doubling the freezing time.
I also placed the bottle on a folded wet paper towel, to increase conduction into the shelf. It cooled at exactly the same rate as the plain bottle- in other words, acted as if it were un-insulated and did not show evidence of improved direct thermal contact.
Finally, I tested the idea that evaporative cooling might be effective. Again, I used three water bottles with identical thermocouples inserted dead-center, but in this case, I wrapped one of the two moist cloth bottles with saran to prevent evaporation:
And the results:
The saran wrapped towel did cool slower than the exposed moist towel as a result of decreased evaporation and perhaps a bit of entrained insulating air.
But the plain bottle cooled fastest. Again.
It turns out it's very difficult to thermally "sink" the wine bottle to the freezer with a simple wet towel. The towel adds mass and insulation, which overwhelms the potential advantages of direct thermal conduction.
But what if we enhanced the effect of evaporative cooling, by adding a fan to the freezer? Sort of an alcoholic "wind chill" factor. Certainly, if your clothes get wet while hiking on a brisk winter day, you can easily die from exposure- Hypothermia3 is insidious. Perhaps if we created a mini-blizzard in the freezer...
Or a gentle breeze. I placed a small, 6" fan scavenged from a computer in the freezer next to a 1L water bottle swaddled in a moist cotton towel. The fan created a 4 mph air current in a nearly empty freezer, chilling the bottle (solid blue curve) almost twice as rapidly as a control (dotted blue curve, a moist towel wrapped bottle merely exposed to stagnant freezing-cold air).
It chilled even faster than a plain water bottle, with or without air motion (compare solid blue to either pink curves, blue curves moist, pink curves dry for comparison4).
As everyone knows, a wet towel and a box fan offers a cooling respite on a hot summer day.
It's for exactly this reason that commercial "blast freezers" are so effective- a large fan forces cold air across the food like an arctic jet stream. Food cools in minutes rather than hours.
Some home-freezer models do contain a small fan, gently teasing air into motion. But the velocities are low, and real-world freezers are stuffed to the gills, blocking air from circulating between last Christmas' ham and those frozen dinners no one likes to eat anymore. In other words, only in a commercial blast freezer does wrapping a wine bottle with a wet towel work. In a home freezer, it actually DELAYS cooling.
So what should you do when in a rush to serve wine with dinner? If you only have ten minutes to spare (and shame on you for drinking a nice bottle of wine in a panic), a bath of ice water will get the job done in 15 minutes5. Direct thermal conduction is very effective. Prefer a drier method? Place the bottle in the freezer (-15F) and it will reach 50F in about a half hour, depending on its initial temperature. Have a bit more time on your hands, and don't want to risk freezing the wine by accident? Store in the fridge (34F) and wait about an hour and a half.
And next time, plan ahead.