Quaffing South African wine won't be a problem during this summer's World Cup but suppliers could take a hit next year as poor weather reduces the grape harvest.

Official figures from South Africa Wine Industry Information & Systems estimate this year's national harvest, which is near completion, will be 6.5% lower than in 2009 and winemaking heartland Stellenbosch has recorded losses of 40%.

The Cape Winemakers Guild trade body said most of its members had reported yields that were between 15% and 35% lower, due to strong winds during the key flowering season last November.

However, despite the substantial volume losses, the cold and wet conditions had improved the quality of the surviving crops, with greater fruit and colour intensity, it added.

"They're still bringing in the grapes, but it looks as though there'll be a double-digit decline on the normal harvest," said Lindsay Talas, buying director at importer Thierry's.

The decision of South Africa's state energy company Eskom to increase the price of electricity for this year and the next two by 25% would also squeeze winemakers, she added.

South African winemaker Dr Paul Cluver of Paul Cluver Wines agreed, saying that as electricity was used in the pumping and cooling processes, the price increase would raise costs in a sector already struggling to deal with the effects of the weak pound.

However, cost pressure from the exchange rate and the knock-on effects of a smaller harvest wouldn't impact shelf prices until the end of the year, predicted trading manager at Musgrave Retail Partners Henry Moran. "The impact depends on your perspective," he said. "The lower yield ought to mean better quality coming through, but South Africa hangs its hat on a very commercial proposition, so we need to make sure it retains that."

South African wine supplies for the World Cup had already been shipped to the UK, so the 2010 harvest would not affect availability over the summer, assured UK market manager at Wines of South Africa Jo Mason.