A Decanter reader in the UK said their Swisscave wine cooler was turned off for nine days during a heatwave, with temperatures hitting 30 degrees Celsius at certain times.
They said the fridge is in a first-floor flat but not in direct sunlight. What might be the long-term effects on the wines, which are part of a growing collection intended for extended ageing?
What happens if your wine cooler is unplugged in a heatwave?
Swisscave’s MD and founder, Hanspeter Jaeger, and expert David Way, of the UK-based Wine & Spirit Education Trust (WSET), highlighted several things to consider but were generally optimistic about the wines’ prospects – particularly given the short period of potential exposure to higher temperatures.
A wine cooler or fridge aims to replicate gold standard storage conditions. This is not only to avoid heat spikes, but also to prevent regular fluctuations in temperature.
‘The conventional wisdom is that wine intended for long-term ageing should be kept in conditions similar to an underground cellar with a temperature in the range of 10–15°C, in the dark and with no vibration,’ said David Way, wine qualifications developer at the WSET.
‘If a wine fridge is unplugged and the air temperature rises to 30°C, then the rising temperature will affect the speed at which the wine develops and, in extreme cases, age [the wines] prematurely and irreversibly,’ said Way.
However, there are several variables.
These range from the temperature of the fridge before its was switched off to the length of time wines are exposed to higher temperatures and the number of bottles in the fridge.
‘The air temperature is not necessarily the same as the temperature of the wine in the bottle,’ said Way.
Even with the cooler unplugged, he also said ‘the wine will have had some protection from both the insulation in the fridge and, further, from the thermal mass of the number of bottles stored together that had originally been refrigerated’.
The more bottles, the bigger the insulation effect. ‘A large fridge that contains 180 bottles will give more protection and for longer than a small fridge with 12 bottles.’
Where wine is exposed to excess heat, some studies have shown that this can reduce levels of SO2, causing a ‘browning of the colour’. This is particularly visible in white wines, he said.
‘However, the good news is that wines intended for long-term ageing typically are to a degree more resilient to the ageing process.’
He added, ‘In comparison to simple wines made for early consumption, they have greater fruit concentration, sometimes higher acidity and, in the case of red wines, colour molecules and tannins which give greater protection to the wine.’
Highly tannic reds should withstand heat better than lighter styles, such as Pinot Noir.
A note of caution would be that some studies have shown that white wines can lose fruity aromas if stored for seven days at 26.6°C (80°F), versus a control sample at 18°C, Way added.
‘When wine was stored at 30°C for a year, it developed faulty characteristics, while wine stored at 40°C showed changes in colour and flavours after only a few days.’
In summary, however, Way said, ‘If the fridge was big enough and cool enough originally, and the exposure to heat was only a matter of a few days, it is likely that the wine will not have been damaged, even if it will for that short period have aged a little more rapidly.’
Humidity and temperature
Swisscave’s MD and founder, Hanspeter Jaeger, said that he wouldn’t expect ‘anything noticeable’ to happen to the wine if exposed to ambient temperatures over a short period of time, such as weeks or even months.
He said it was ‘certainly a different story’ if bottles are exposed to frequently changing temperatures or even 30°C heat with very dry humidity for a longer time, such as years rather than months.
‘Many wine lovers have this scenario in mind and get nervous when their wine bottles are at ambient temperatures for days or weeks. They should not,’ said Jaeger.
‘Low levels of humidity will, over time, damage your wine,’ said Sebastian Riley-Smith, founder and MD of Smith & Taylor, in the latest issue of Decanter magazine.
‘Fine wine should be stored at 65-70%, allowing the best corks to permit only 1mg of oxygen to enter the bottle per year. This moderates the process of wine developing complexity, softening tannins, and keeps the identity and vital statistics secured to your bottles.’
One potential issue in the shorter-term was that higher temperatures can cause the wine bottle to expand slightly, he said.
‘If the cork is not perfect (and many corks are not), then it may happen that a little wine presses through the cork to the outside. Now there is a liquid bridge between inside and outside, which over time (several months or longer) can bring oxygen to the inside. If this happens the wine may go bad.’
He said that in a situation ‘where the wine was at a very high temperature for weeks, I would advise [people] to check the corks’ – although this can be difficult depending on the bottle. If wine spots are visible on the cork, then it may be better to drink the contents of the bottle sooner.
Callum Dooley, director and UK sales manager of Elite Wine Refrigeration – official UK partner to Swisscave – also said that the thermal mass of the wines inside the fridge should mean that ‘it will only be a few days where the wine may have been slightly warm’.
Published in August 2020 and updated in June 2021.