Whether one wants to chill champagne or bring wine up to room temperature, it pays to be patient.
EVERYONE KNOWS THAT CHAMPAGNE is best drunk chilled. But how long does the bottle need to be left in the refrigerator? Does it matter whether a child comes along and opens the door of the refrigerator in the meantime? Or say you want to bring wine up from the cellar in order to warm it to room temperature before a meal. How far in advance should you do this? The use of a thermocouple, a device that precisely measures temperatures, gives gourmets useful orders of magnitude.
Let’s start with the bottle of champagne. In a simple experiment, the probe of the thermocouple was inserted and the bottle placed in the door of a refrigerator at thermal equilibrium next to bottles that had been there for more than two days and that recorded an internal temperature of 11°C (52°C). The initial temperature of the bottle of champagne was 25°C (77°F). Measurements taken every ten minutes showed a slow cooling: After 30 minutes the temperature of the champagne was still above 20°C (68°F), and it took three hours to reach 15°C (59°F). Only after six hours did it fall to 12°C (54°F), proof that glass is a poor conductor of heat (which propagates in it solely by conduction, whereas in water heat is distributed by convection as well).
Untimely Openings
Suppose you have taken this strong thermal inertia into account, but then a child comes along and opens the door of the refrigerator. Is there a risk that the champagne you have gone to the trouble of chilling all this time will now be warmed up?
This time the temperature in the refrigerator was initially 8°C (46°F). Outside the temperature was 20°C (68°F). When the door is left open for only seven seconds, the temperature rises to 11°C (52°F); after a few minutes it goes back down to 8°C (46°F). When the door is left open for twenty seconds, the temperature rises to 18°C (64°F), then drops rapidly at first and slowly afterward. The air inside the refrigerator heats up very quickly, then, because the cool, dense air inside flows out from the bottom and is replaced by air entering from outside. But this heating up involves only the air itself, not the bottles, whose calorific capacity—and thermal inertia—is substantial. The temperature of the bottles themselves rises hardly at all as a result of a momentary opening of the door, and after a few minutes they cool back down with the rapid drop in the air temperature.
Up from the Cellar
The opposite question, how long it takes to raise the temperature of a wine, has also been neglected. Say you are looking forward to dinner at home with friends and you want to bring up a good bottle from the cellar. Suppose, too, that your guests happen to know that the wine should be drunk at a temperature of 18°C (64°F), but the temperature in your cellar is 12°C (54°F). How far ahead of time should you bring the bottle upstairs?
Naturally one could work out the answer using the laws of physics. But let’s conduct a little experiment and measure the actual change in temperature over time. Bring up a bottle of wine whose initial temperature is 9°C (48°F). If the temperature in the dining room is 24°C (75°F), we will find that it takes about half an hour for it to reach a temperature of 12°C (54°F), three-quarters of an hour to reach 14°C (57°F), an hour and a quarter to reach 16°C (61°F), an hour and three-quarters to reach 18°C (64°F), and more than three hours to reach 20°C (68°F).
The long period of time needed to bring a bottle up to room temperature again results from its low thermal conductivity, especially when the difference in temperature between the room and the bottle is small. The answer to our earlier question, then, assuming the same ambient temperature, is that the bottle must be brought up from the cellar more than an hour before dinner is served. This is not a detail to be left to the last minute.
Bottles Versus Glasses
Given these measurements, can we deduce the time needed to bring wine up to room temperature if it is summertime and the temperature inside is 27°C (81°F)? Alas, no; further measurements are needed, together with the equations of thermodynamics. But for our purposes it will suffice to consider certain orders of magnitude. If the temperature of the bottle to begin with is 12°C (54°F), it will take about eighty minutes for it to reach 27°C (81°F). But if room temperature is only 19°C (66°F), it will take more than two and a half hours, starting from the same initial temperature. It also turns out that the upper part of the bottle warms up more quickly than the lower part. The difference may be as much as 4°C (7°F), which produces significant differences in taste between the first and last sips of wine because the higher the temperature, the more quickly its aromas evaporate.
Finally the guests are seated. Once the wine, warmed to 16°C (61°F), has been poured into their glasses, how fast will it heat up when the ambient temperature is 23°C (73°F)? This time, the temperature in a traditional glass increases on average by 0.2°C (0.36°F) per minute, which ought to be enough to stop us from pouring the wine until our friends are ready to hoist their glasses.