My wine cellar is below my front porch. The temperature from September to June averages 16, but in July and August can creep to 21 for 10 or 15 days. How does the temporary rise affect the maturity date of my wines? I assume there could be a 10-per-cent acceleration in maturity.
I suspect your guess is in the right ballpark.
I am unaware of a scientific study replicating the rough conditions you cite, but I would have ventured an estimate of somewhere between 10 and 25 per cent. As you imply, elevated temperatures accelerate the chemical reactions that contribute to wine's flavour evolution over time. Ideal cellar temperature of 13 C is believed to achieve the most beneficial evolution over the long haul, but one need not have an expensive, climate-controlled room or fancy wine fridge to obtain reasonably favourable results more quickly. If you're looking for good results over 10 years for most wines, a so-called passive (or non-air-conditioned) cellar is fine in most parts of the country, providing it's properly insulated from the warmer regions of the house.
Many wine pros believe that a sustained period above 21 Celsius – I'm talking a couple of months a year – is a big no-no and will lead to cooked and other unpleasant flavours. In other words, a kitchen counter or main-floor broom closet is no place to "cellar" wine. You should also be wary of regular, significant fluctuations in temperature, either daily or throughout the year – up-down, up-down. As the liquid expands and contracts because of the swings, it will draw in and push out air through the cork's pores like a pump, eventually oxidizing prematurely, leading to off flavours.
I'd say you've got reasonably good conditions in your home (even if it's not the optimum space for pricey Bordeaux or Barolo for long-term storage). A gradual seasonal migration from 16 to 21 and back, providing the temperature remains at 21 only for a few days, should be fine.
In a study published in 2012 in the Journal of Wine Research, a team led by C.E. Butzke of Indiana's Purdue University found that wines shipped across the United States in non-refrigerated containers were in some cases exposed to temperatures as high as 44 C and to daily swings of as much as 4 to 21 degrees. Using complex scientific models for wine aging, the researchers concluded that, in the course of their brief transport to market, some wines were exposed to heat corresponding with added bottle age of between one and 18 months compared with wine stored under ideal cellar temperature. I'm not sure what this implies for your specific case, but it sounds to me as though wine would be much safer for years in your basement than it would be for a couple of weeks in a truck on the road.
For Ontario readers: Vintages will host a "Taste the Classics" preview from 6:30 to 9 p.m. on Nov. 26 at Liberty Grand in Toronto. Among the more than 65 wines to be poured are the Masseto 2010 from Tuscany's Tenuta dell'Ornellaia and Vega-Sicilia Unico 1999 from Spain. Tickets are $125 a person. Further information at vintages.com.
Beppi Crosariol is the co-author, with Lucy Waverman, of The Flavour Principle, a sumptuous new cookbook and drinks compendium, published by HarperCollins.