"Heat is wine’s greatest enemy," advises James Laube, senior editor of Wine Spectator. When wine is exposed to temperatures over 70 degrees Fahrenheit for a significant amount of time, the heat can damage it irrevocably. Above 80 F, the wine begins to, quite literally, cook, a phenomenon known in the wine industry as maderiziation. There is nothing more damaging to the long-term health of the wine -- heat fouls the bottle, the seal and the wine inside. According to Laube, "even a few minutes of sizzling sunshine can ruin your prized possessions."
The Science (and Hazards) of Heat
Heat exposure has multiple, profound effects on wine. First, heat reacts with many of the flavor- and color-producing compounds in red wine, prematurely releasing the flavor precursors bound to the glucose sugars in the liquid. This changes the wine's sensory character irrevocably. Heat exposure can also cause the formation of a hazardous compound, ethyl carbamate, proven carcinogenic in rodent-based experiments. Ethyl carbamate forms when urea, naturally present in wine, spontaneously reacts with alcohol -- a process that is exponentially increased with the application of heat.
When a bottle of wine is exposed to high temperatures, the liquid expands inside the bottle. The pressure of the expanding liquid may force the cork upward from the neck, resulting in what is referred to in the wine business as a “pushed” or “raised” cork. The expanding wine may also find its way around the cork and leak. Beyond the sticky results of heat-leakage, the migrating liquid often damages the bottle's seal, which allows air into the mix and results in an oxidized wine.
Flavor and Color Changes
"Cooked" wine tastes, unsurprisingly, as if it has been cooked on the stove. The wine's rich fruit flavors lose freshness, tasting stewed, baked or burnt. Maderated red wine often smells like canned prunes or processed jam -- overtly sweet and somewhat caramelized, but thin, one-note and characterless. And because heat exposure decreases the levels of free sulfur dioxide, which has protective effects, maderized wine changes color, too. Instead of showing a crystalline deep-red, the color deepens into a brownish -- sometimes, brick-red -- tone that hides behind the dark glass of the bottle but is immediately apparent once decanted.
To avoid the heartbreak of a "cooked" wine, be savvy in the way you buy and store your oenological treasures. The first protocol is simple: Never, ever leave wine in your car. When you're parked in the sun, the temperature in your trunk can reach well above 100 F. Treat your bottle of wine with the same care as a quart of ice cream -- carry it in the passenger compartment, not the trunk, and rush it home from the store. Another tip: When temperatures soar, limit your wine-buying to stores with climate-protected receiving docks.
Protect your wine collection at home by maintaining a steady temperature of around 55 F. It's best to store wine in your cellar or basement and never the attic, which experiences significant fluctuations in temperature. The best storage is, of course, in a purpose-built wine fridge with rigid temperature controls.
- Wine Spectator: Beware of the Heat
- Wine Spectator: Is There a Way to Measure (and Beat) the Heat?
- ine Spectator: Ask Dr. Vinny: What Does "Cooked" Wine Taste Like?
- Wine Folly: Wine Faults
- Wine.com: Wine and Heat – Eternal Enemies
- The Academic Wino: Evidence for Damaging Effects of Heat Exposure on Wine During Transport and Storage and Recommendations for Protection
- Photo Credit Jack Hollingsworth/Photodisc/Getty Images