Italy is set for one of its smallest wine harvests after an arid, torrid summer – and will almost certainly cede its title as the world’s biggest wine producer to France.

Growers say scorching temperatures and meagre rainfall have affected crops, but add that predicted autumn rains could save the quality of a vintage that has so far been disappointing. The exceptional weather brought forward the harvest in most parts of the country by two weeks or more. White wine producers in the north began in mid-August.

Last year Italy topped the list of international wine producers, but France is expected to overtake it with a predicted bumper harvest.

A survey released on Tuesday by the Italian Wines Union (UIV), and a government body, Ismea, forecast that production would fall to barely 42m hectolitres – 10% below last year’s level. In Spain, too, a relatively modest harvest was predicted: officials said the yield would drop to below 40m hectolitres, which would be 5% lower than in 2010.

France, by contrast, was expecting a bumper vintage of almost 48m hectolitres – a 6% increase on the previous year. There, big swings in the weather were reported to have split growers on the timing of the harvest, leading to the possibility of widely varying qualities within the same vintage.
Hot, dry weather dehydrates the grapes, reducing the yield. But it also generates proportionately more sugar in the fruit and – with the help of some rain – can produce excellent vintages.

“It means less, but better, will be drunk,” declared Lamberto Vallarino Gancia, the president of another body representing the Italian wine business, Federvini. But his optimism was not shared by the government agency, Ismea.

“Caution is needed this year as never before,” it said in a statement which pointed to “significant downturns” in the quality of the early harvested grapes.

It added, however, that “rainfall in the next few days could improve the situation of the late-harvested ones”.

Italy’s wine production has fallen below the 43m hectolitre mark on only two occasions since the mid-1950s. But then August was the eighth driest – and 10th hottest – month in the country for almost two centuries.

So far, September too has been unseasonably hot: in the Tuscan wine producing region of Chianti the temperature on Wednesday peaked at 32C (90F). But rain is forecast there, and in several other parts of the country, early next week.France had a dry spring, followed by a wet July and August that may have disappointed holidaymakers, but irrigated the vines and held out the promise of an exceptional vintage.

The Beaujolais harvest started on 24 August, the earliest date since the exceptionally hot summer of 2003. But Melina Condy, of Inter Beaujolais, told Reuters: “The small berries boast an excellent juice to skin ratio. This is great news as the compounds that give the red wine its wealth of colour and tannin structure are mainly to be found in the skin.”

In Chablis, some growers began their harvest on 30 August, while others waited until 5 September. Among those who held off was Daniel-Etienne Defaix, who said the delay could make a crucial difference to the quality: “This year, we could see that, with time, there appears to be two different 2011 vintages with a different imprint by man.”