By Alexander (Al) J. Pandell, Ph.D.
There are three storage conditions of concern to collectors and consumers of fine wine: light, humidity and temperature. The storage area for wine must be dark because ultraviolet (UV) light will damage wine by causing the degradation of otherwise stable organic compounds found in wine. Since these organic compounds contribute to the aroma, flavor and structure of the wine, the changes caused by UV light result in the deterioration of the essence of wine. (Note: Fluorescent lights emit a significant amount of UV light.)
The only reason humidity is an issue in wine storage is because of the use of the traditional cork seal. The relative humidity of the storage area (i.e., the amount of gaseous water in the air) can exacerbate the rate of evaporation of wine from the bottle if the cork is defective. Since corks are far from perfect in their ability to seal a bottle of wine, ullage (the space between the bottom of the cork and the wine level in the bottle) develops in almost all bottles stored for extended periods due to evaporation. If the cork (seal) is defective, low humidity in the storage area will result in wine moving out of the bottle faster over time and significant ullage will develop in less time under these conditions. Thus, the more important issue is the quality of the cork seal and not the relative humidity in the storage area. Of course, very low humidity can dry out the cork leading to sealing problems.
Assuming one has good cork seals, and a non-drying (i.e., moderately humid) and dark storage area, the most important factor in the storage and aging of wine is temperature. If you ask most anyone associated with wine, from collector to so-called expert, they will most likely tell you that the ideal storage temperature is 55° to 60°F. According to conventional wisdom, wine develops most harmoniously if stored in this temperature range with little or no fluctuation. So, for example, an excellent storage temperature would be 55°F with a fluctuation of plus or minus one degree. A well-known wine personality and executive from Burgundy told me recently that the ideal temperature for wine storage is 13°C which is equivalent to about 55°F. Degrees (°) C refers to the Celsius temperature scale on which water freezes at 0°C and boils at 100°C. This scale is used throughout Europe and most of the world. The 13°C temperature makes historical sense since wine storage in France is typically in caves and the natural underground temperature is around 13°C. Thus, the "ideal" seems to have been the result of regional custom and practice rather than scientific study.
What will happen to a wine stored at room temperature (73°F) in a dark closet rather than in a temperature-controlled environment of 55°F, the commonly accepted "ideal" temperature? This is the question I will attempt to answer in the following discussion. To do this, we must consider some chemical principles to help us understand why high temperature is detrimental to wine.
Bottle aging of fine wine is a result of many chemical changes (reactions) taking place over time. Each of these reactions occurs at a certain speed or rate, and each reaction is affected differently by temperature changes because each has a unique energy factor or natural energy barrier, the "hurdle" that must be overcome ("jumped over") for the reaction to occur. Using well founded and accepted chemical principles that will not be discussed here, one can estimate the effects of temperature increases above the (assumed) ideal 55°F on the increase in rate or speed of aging. These calculations are made assuming two different energy barriers, or hurdles for reaction to occur, (low and high) and three different temperature changes, 55° to 59°F, 55° to 73°F, and 55° to 91°F. By choosing the low and high extremes for the energy barrier, one can be fairly certain that the true reaction barrier lies between these extremes. After examining reactions similar to those that occur in wine during aging (e.g., oxidation, reduction, esterification, etc.), I am persuaded that the true reaction barrier lies closer to the high energy barrier than the low energy barrier. The results are summarized in the table below.
|How Temperature Can Affect The Rate Of Aging of Wine
|INCREASE IN RATE OF AGING ASSUMING ENERGY BARRIERS TO REACTION ARE:
The first two columns in the TABLE show the temperature change, and the third and fourth columns show the increase in the rate of aging associated with each temperature change based on LOW and HIGH energy barriers. For example, the first row shows a temperature change of 55°F to 59°F with a calculated increase in the rate of aging of 1.2 times assuming a LOW energy barrier and an increase of 1.5 times assuming a HIGH energy barrier. One can conclude from these calculations that the increase in the rate of aging for a temperature change of 55°F to 59°F is between 1.2 and 1.5 times. This means that if your cellar is at 59°F instead of 55°F, your wine ages 1.2 to 1.5 times faster than if it were at 55°F.
As the data in the TABLE show, going from 55°F to 73°F, an increase in temperature of 18°F(10°C), doubles the rate of a reaction if it has a LOW energy barrier. If the reaction has a HIGH energy barrier, the rate of the reaction increases by a factor of eight for this temperature difference.Translated, this means if your cellar is at 73°F instead of 55°F, your wine ages 2.1 to 8.0 times faster than if it were at 55°F. Thus, 3 years at 73°F is equivalent to between 6.3 and 24 years of aging at 55°F. These differences are very significant.
It gets worse as the temperature difference increases. As seen in the TABLE, a change from55°F to 91°F increases the rate 56 times for reactions with HIGH energy barriers and 4.1 times for reactions with LOW energy barriers. So if your storage is at 91°F instead of 55°F, your wine ages 4.1 to 56 times faster than if it were stored at 55°F. One month of aging at 91°F is equivalent to between 4 months and 18 years of aging at 55°F. As stated earlier, the "true" situation probably closer to the 18 year end of the range. These calculations show that higher temperatures markedly speed up the aging process and result in maturation of a wine over a very short time.
But it doesn’t end there. Another concern is that higher temperatures will result in undesirable chemical reactions taking place that were either too slow or nonexistent at the lower temperatures. I think this is as important an issue as speeding up changes that have a desirable effect on the bouquet of a wine as it ages. If these undesirable reactions have HIGH barriers to reaction, which is very likely, then over a moderate aging period for a quality red wine, say 15 years at 55°F, little reaction has occurred and the wine is relatively unaffected. But, if the storage temperature is 73°F,the undesirable reactions will have occurred 8 times faster which means the same reactions have occurred in less than 2 years. Another way to put is that 15 years at 73°F is equivalent to 120 years (8 x 15 years) at 55°F. Of course, very high temperatures for even relatively short periods can lead to nasty reactions producing compounds with foul odors and off tastes. This situation undoubtedly prevails at temperatures above 90°F where the rates of high energy barrier reactions increase by a factor of 56 times or more.
In summary, doubling, tripling or quadrupling the rate of the desirable reactions is not the only issue in the aging process. Increasing the rates of UNDESIRABLE reactions that are very slow at lower temperatures may be an equally or more important issue. Higher storage temperatures make available many new pathways for desirable AND UNDESIRABLE reactions. Chaos reins in the bottle!Excessively high temperatures for several hours will surely have a detrimental effect on a wine’s chemistry with the production of off-flavors resulting from oxidation and other undesirable reactions whose rates have been dramatically increased by the higher temperature. It is not going to matter what temperature YOUR cellar is if somewhere along the distribution line the wine is COOKED on the dock or in a hot warehouse.
What does one see and taste in a heat damaged wine? One important indicator of heat damage is color. Pre-mature browning can be an indicator of oxidation due to heating. A brick edge in a young red wine is a telltale sign of oxidation due to excessive heat. Since Sherry is an oxidized wine,another indicator of heat damage in table wines is a sherry-like taste.
If 55°F is better than 73°F for wine storage, why isn’t 49°F better than 55°F? It may very well be! Clearly, the rates of all reactions will be slowed even more at the lower temperature. However, 49°F may be too low a temperature to allow some desirable aging changes to occur at a rate that is comparable to the human life cycle. Remember from our earlier discussion that different reactions are affected differently by temperature changes because each has a different barrier to reaction. Reactions with high barriers are more sensitive to temperature changes and with decreasing temperature will slow down more than reactions with low barriers.Since the harmonious aging of wine is due to many different chemical reactions occurring in a naturally orchestrated manner, the lower temperature may slow down some reactions to the point where they become non-contributors to desirable flavors, and, therefore, the wine’s evolution is thrown out of sync. It would be interesting to carry out research on this, but the time line required is beyond that of most humans.
As a final thought, and in keeping with the discussion above, be sure to store your opened bottle of wine in the refrigerator. If you must keep an opened bottle of wine for a few days, the best place to store it is in your refrigerator which is typically at a temperature of about 41°F (5°C). The chemical reactions leading to spoilage (primarily oxidation-reduction) will be slowed down by a factor of 6 to 16 times compared with storage at room temperature (about 73°F). Therefore, a wine should last 6 to 16 times longer in the refrigerator than at room temperature. Red wine can be poured in a glass and allowed to slowly warm before consumption or put in a microwave oven for 15-20 seconds.
Re-published from The Alchemist’s Wine Perspective™, Issue One, November 1996.© 1996, 1998 by Alexander J. Pandell. All rights reserved.