Global warming and winemaking

Remedies for high alcohol content

By Ian Hickinbotham
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Ian Hickinbotham, author of Australian Plonky

Ian Hickinbotham, author of Australian Plonky

Australian Plonky by Ian Hickinbotham


Increasing alcohol content of table wines, due to global warming, is concerning wine drinkers in all countries. Wines that were 12 percent alcohol can now be 14 percent alcohol when made from the grapes of the same vineyard.

The simplest proof of global warming and perhaps the simplest to understand was related to me by oenophile and marine biologist, Mike Sugden.

The acidity of the sea is increasing: that is measurable. Even if you did not do school chemistry elaboration is simple. Carbon dioxide is represented by the formula CO2 (the '2' spells the 'di’ of ‘oxide') and when dissolved in water (CO2 + H2O), it becomes H2CO3, a very weak acid that was probably the first disinfectant of surgery. In fact, when you drink straight soda water, you are really drinking carbonic acid.

So, for the sea to become increasingly acidic, the carbon dioxide can only come from the atmosphere above it.

Experiments are continuing apace in universities in many countries to remove part of the alcohol content in normal table wines. It should be understood that for such wine types, the most popular the world over, all of the grape sugar is fermented by yeasts into alcohol (and gas). It has ever been thus, since time immemorial.

Nowadays, winemakers can stop a fermentation before all of the alcohol is developed. But such wines contain varying amounts of sugar, the grape sugar that has not been fermented, and generalising, though we might like them when young, universally our taste preference is for wines without that residual sugar. And it has taken some 10,000 years at least for our tastes to be so entrenched. We do appreciate sweet wines but only occasionally and we do not drink much quantity in normal social circumstances: at least that is the circumstance in those countries that have an entrenched wine consuming culture.

Importantly, alcohol, as such, tastes slightly sweet though somewhat imperceptible. Ordinary vodka is the least flavoured of the spirits: it is not even aged in oak barrels – and it is possible to taste its slight sweetness.

Distillation is an obvious treatment, but heating a wine to boiling point is very severe. So trials are done at low temperatures in a near vacuum.

Reverse osmosis is perhaps the most promising and available, but rather technical to explain. The most meaningful explanation of osmosis itself is the well known fact that if we drink seawater we eventually die because our internal membranes allow transfer of the salt itself to other organs. Reverse osmosis works because small molecules pass under pressure through a membrane more easily than large molecules.

Whatever, experiments so far indicate (as might be expected) that professional and experienced wine drinkers do not like alcohol-reduced table wines. New wine drinkers, however, are not so positive and maybe the market for partially de-alcoholised wines is well into the future. At least such consumers may not be so critical of the potential gross interference with winegrowing, the worst in wine's long history.


Ian Hickinbotham, one of the most innovative and influential oenologists in Australia over his 50 year career, is the author of Australian Plonky (see related review below).


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October 31st, 2012
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