Wine 101: Passive Wine Cellars
Passive wine cellars use ground temperature to moderate the temperature swings and make the temperature swings seasonal instead of daily. Whereas refrigerated wine cellars can go anywhere in your house, a passive wine cellar must be located in a subterranean basement.
Annual Temperature Can Fluctuate
The graph above charts ground temperature variation over a year by depth below ground level. This chart is for a temperate climate and can vary if you go north to a colder climate or South to a warmer climate.
I picked two ground depths for discussion 7’-6” for an average basement ceiling height in an older home and 9’-6” for an average height in upscale newer homes. The funnel which looks like a champagne glass is the high and low temperature of the soil at a given depth. The closer you get to the surface the temperature of the soil swings broadly from summer to winter with an mean of 56 degrees. At 7’-6” which is represented by the first horizontal line the soil temperature varies from a low in the winter of 48 degrees and a high during the summer of 64 degrees with the mean of 56 degrees. At 9’-6” the temperature seasonal swing is 51 – 61 degrees. 55 to 56 degree is considered the ideal wine cellar temperature. Why, mostly because of convention. The European wine cellars of the famous wineries in Europe store their wines in deep caves, which are frequently stone quarries from Roman times. These caves are usually 20’ deep or more. At that depth they stay at the mean temperature of 56 degrees plus or minus less than one degree over the year.
A passive wine cellar in a home can never achieve the tight temperature range of the deep caves but it can make the swings moderate and seasonal. At 7’-6” the temperature swing is 16 degrees from 48 -64 and at 9’-6” the swing is 10 degrees 51-61. Without going into the why, which is the subject of another blog, the lower the temperature that wine is stored at the slower it ages. Temperature swings if significant, 14 degrees or more, cause your wine to breathe through the cork which increases the aging process significantly. If the temperature swing is seasonal the damage is much less then if it is daily by a factor of 365 days.
To create a passive cellar in your home basement, you allow the cool temperature from the floor to enter while you block out the higher temperature from the house and higher ground levels on the exterior walls. The diagram above shows a passive wine cellar construction detail. By using a vapor barrier and high R value insulation, you block temperature exterior to the wine cellar and allow the ground temperature from the floor to enter. In this case the exterior concrete basement wall was insulated on the outside but it can also be insulated from the inside. To this you need to add an exterior grade door with full 360 degree weather seal around it.
Higher temperatures and significant temperature swings accelerate the aging process which is not necessarily a bad thing if done on a controlled basis like a passive cellar. It just means your wines are ready to drink earlier. Where this does make a difference is maintaining your wine in the optimal drinking range once they have peaked. Many whites and some reds are at their peak when bottled. Some reds take years to age to their peak. Once at their peak you want to keep them there to enjoy as long as possible. The proper cellar environment is the key. A refrigerated cellar gives you total control but a passive cellar is the next best thing.
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