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What is the perfect cellar temperature?

Here's an important area where the science is not fully formed, though a sufficient consensus exists to give useful advice.The uncertainty arises from the different storage environments that exist in different countries around the world. The ambient temperature in warehouses and cellars in Burgundy, for example, or in Spain, has been higher than in Britain, yet these are regions with traditions of long term cellarage.

Which is better? For many years I for one took the view that the model was the cellar underneath a top Bordeau chteaux - what was good enough for them was good enough for the rest of us - until I visited one in a particularly hot summer when the cellar temperature must have been in the upper 20s Centigrade. I believe that air-conditioning has now been installed.

Global wine trading and global warming has changed the pitch to the extent that we have witnessed a growing awareness of the importance of temperature and an unwillingness to tolerate risk of heat damage. Temperature and humidity audits are seen as more critical and you can now buy 24/7 monitoring systems that alert you via the web, wherever you are in the world, of any deviation from the pre-set norm.

So what should be the norm? I have heard advice suggesting that an all-year temperature of below 12 (Centigrade throughout) is the best; Jancis Robinson supports 13. In winery cellars where I have checked the thermostat I have observed 14.

It does depend on the wine to some extent as some are less sensitive than others; but if you have a mixed cellar then I would opt for an annual range which does not fall below 10 and does not rise above 20. Why a range? Back to Bordeaux chteaux for a start, which have always experienced summer/winter variation. There may just be a benefit in this for the natural evolution of wine.

But energy usage is an increasingly important point. Working with rather than against seasonal changes in temperature will impose substantially lower energy demands on your refrigeration system, which is good for your pocket as well as for the environment, and with no evident detriment to your wine provided limits are not exceeded.

However staying within the limits is not always easy to do, even with air-conditioning. There will always be a lag between temperature change and the control response. Very short term spikes in temperature - less than 24 hours - may not be dangerous owing to the thermal inertia of wine inside its bottle and inside its case. But even short-term temperatures above 25 may cause long term damage and should be considered unacceptable. Somewhere around this level corks may be dislodged through expansion; and heat damage results in chemical changes which are irreversible.

At the other end of the spectrum, if the ambient temperature falls below 12 for any length of time the rate of evolution slows noticeably, not always ideal if you want to drink the wine in your lifetime. And below 5 there is a different risk, that of accelerated precipitation, either of tartaric crystals (white wines) or of anthocyanin-derived matter, pigmentation and tannins (red wines). Bottles kept at domestic fridge temperatures for long periods can lose flavour intensity too.

Humidity is even harder to pin down. The range is 0-100%, with 100% representing precipitation - rain, in effect. This is almost certainly ideal for the wine itself but distresses capsules, labels and cartons. Somewhere below 50% will avoid the effects of damp (though the impact itself is temperature-dependent) but there is a growing risk of evaporative loss from within the bottle, 'drying out of the cork' as it is sometimes loosely called. What's the control figure? Somewhere between 60 and 80%, though the higher the temperature, the lower the humidity needed to achieve a constant moisture content.

So that's the chapter and verse, but it's far from Gospel. There was a report last year of 1907 vintage champagne recovered from a shipwreck off Finland after almost a century under the sea. The bottles were totally immersed so the humidity was a guaranteed 100%. Temperature was not given, though the range experienced on the Finnish coast is probably somewhere between 5 - 10C. And it would certainly have been stable. The wine was, as reported, delicious and still youthful, apparently in a state of suspended animation.

And every bottle of Australian, Chilean, South African and New Zealand wine consumed in the Northern Hemisphere (including UK and USA) has crossed the equator. Unless in a 'reefer' (refrigerated container) it will have experienced a few days at massively above 20C. I once saw a max/min thermometer taken out of a container of Australian wine which had just arrived in the UK. It registered an upper reading of 53C. The wine itself was unaffected. It was young and robust, of course, but this finding was a source of reassurance nevertheless. In fact I have never, to my knowledge, come across a shipment-affected bottle of wine from one of these sources.

But contrary to this is the widespread experience from the US of mature claret advancing more rapidly than the same wine cellared in the UK. 1982s for example, which many critics see as over the hill in the US but still reasonably fresh and alive in the UK today (2008). Most American collectors are assiduous over their cellar environment, so the explanation is less than clear. Something to do with shipping through the Panama Canal, perhaps?Hugo Rose is a Master of Wine specialising in evaluating fine and mature wines. He is a regular judge on Decanter panels and has written on food and wine, terroir and the en primeur system.

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