A spate of hot and humid weather has led many Bordeaux estates to bring forward their Merlot harvest, as overall conditions remain 'hugely challenging'.

Almost every classified property in Margaux, including Palmer, Lascombes and Chateau Margaux itself began harvesting Merlot grapes on 27 September, as did Chateau Latour in Pauillac.

Merlot had been expected to remain on the vine until early October. Cabernets are now likely start on 4 October, also a few days earlier than anticipated, as estates seek to make the best of a tough year by balancing ripeness against the threat of rot.

‘There is no longer hope for a great vintage, that is over,’ Stéphane Derenoncourt, consultant for estates across Bordeaux and including Prieuré Lichine in Margaux and Petit Village in Pomerol, told decanter.com.

‘It is a vintage for rich winemakers; those who have the means to spend the necessary time, care and effort. The wines will have aromatic intensity but many will lack tannic maturity.’

However, he said low Merlot yields mean there has been ‘just about enough time for them to concentrate the sugars and reach phenolic maturity’.

The Bordeaux 2013 harvest is set to be the region’s lowest since 1991, and down by 20% versus last year, according to official estimates.

David Pernet, consultant with Sovivins, said, ‘the key factors for quality this year will include a light fruit load, grass-covering between the rows to soak up excess water, good green harvesting, early intervention against rot, careful sorting and plot-by-plot measurements of maturity’.

The onset of rot is causing increasing concern, although an improved weather forecast, with cooler nights and a north wind, could help to aerate vines.

‘For the moment, clay soils are resisting the best, as they are more acid, meaning rot doesn’t spread as fast,’ said Derenoncourt.

‘It’s very hard to say what is going to happen. We have fought like dogs all year against the weather, and it’s still hugely challenging.’

Written by Jane Anson in Bordeaux