Once a wine departs the comfort of the winery, it can have a long way and a long time to go before it is opened and enjoyed. Proper transportation and storage become an important part of ensuring that what the consumer drinks is what the winemaker intended.
One factor that causes particular concern for everyone along the chain, from producer to distributor to consumer is heat. Many importers and producers insist on temperature-controlled transportation when sending wine across a country or across the planet, and experts will frequently tell you that a cellar with a constant temperature–somewhere in the range of 10 to 15°C (50 to 59°F)–is essential for good conservation of wines, especially for long-term aging. While there is a certain leeway, in terms of the conditions that will allow a wine to evolve without significant problems, there are limits that should be kept in mind.
One thing that is very clear is that lower temperatures correlate clearly with better conservation, especially over the long run. At higher temperatures–anything above 20°C, certainly–a number of chemical reactions accelerate significantly, leading to accelerated oxidation and thus, premature aging of the wine.
At the American Chemical Society’s 2014 National Meeting in San Francisco, Dr. Fulvio Mattivi, of the Edmund Mach Foundation in Trento, Italy, presented a study where a set of Sangiovese wines were stored under two different conditions over a period of two years: one in “professional” storage conditions, at 15 to 17°C (59 to 62°F), and another in the conditions mimicking those of an Italian apartment without air conditioning (68 to 80°F). The results were quite dramatic. With a wine aged for six months under the domestic conditions showing as “old” as the wine aged for two years under the controlled conditions. The wines under the domestic conditions were aging four times as fast!
At higher temperatures, SO2 levels in the wine drop faster, along with the levels of antioxidants and some aromatic compounds, leading to cooked or Sherry-like aromas as well as significant browning and/or loss of color, among other unfavorable consequences. It’s certainly not what most people will be looking for in their Beaujolais or Napa Cabernet. For Dr. Mattivi, awareness of the significant effect of storage conditions should be in consumers’ minds when they get a bad bottle of wine: “If I buy a wine I know at a shop and it is showing below expectations, perhaps I should go find out about storage conditions.”
Fluctuate without sinking
Saying that lower temperatures are better is not the same, however, as saying that a wine that spends some time in a higher temperature will automatically be ruined. Research conducted by Wessel du Toit, a professor at Stellenbosch University, in South Africa, seems to point out that variations in temperature are less important than the total number of heat units that accumulate over time.
In a study meant to mimic the effects of transportation on South African wines to their primary export markets in the Northern Hemisphere, du Toit exposed wines to variations in temperature ranging from -4°C to 37°C, as if the wines had spent a while on the docks in the South African summer, before arriving at their destination in the middle of European winter. Three other sets of wines were stored in three constant temperatures: -4°C, 15°C and 37°C.
The study points out that high temperatures were clearly to be avoided. After only two weeks of storage at constant temperatures, the wines stored at 37°C and 15°C showed significant differences in sensory panels.
More surprisingly, variations in temperature were not as significant as constantly high temperatures. In sensory tests and chemical analysis, the wines that had gone through the variations in temperature performed fairly similarly to the ones stored at a constant 15°C. For the Chenin and Sauvignon Blanc used in the study, in any case, heat units mattered more:
It thus seems that temperature variations does not seem to play such a large role in white wines matured in the bottle, but rather the average temperature it is exposed to. A white wine thus stored at say 2 – 12’C (which is a temperature variation of 10’C), will thus age much slower than the same wine left at say 20 – 22’C (which is a temperature variation of only 2’C).
That seems to indicate that if you store your wine in the basement of your home, and that temperatures follow a slow curve of heating and cooling over the seasons, that will probably not have any major effects. The key factor is more the accumulation of excessive temperatures, which add up over time in creating adverse consequences.
Interestingly enough, du Toit also points out that beyond the oxidative “maderization” of overheated wines, some of these negative effects are felt even if the wines are being protected from oxygen:
High temperatures are known to increase acid hydrolysis of certain fruity esters, as well as the hydrolysis of 3-mercaptohexanonacetate, which is responsible for the passion fruit and guava aromas in Sauvignon and Chenin blanc wines (Coetzee et al., 2012). These breakdown reactions do not need oxygen and can thus proceed even if the wines are closed under screw cap, which should be kept in mind by the producer when shipping or storing wines.
In other words, when a wine suffers from the heat for any prolonged period of time, a lot of bad things start to happen. Wines can easily get the summertime blues.