Baboons have devoured tons of grapes - enough to fill thousands of wine bottles - in a series of brazen raids on farms in the heart of the Cape winelands.

Farms in the fertile Franschhoek Valley are being stripped by troops of Chachma baboons, despite guards in the vineyards.

Mark Dendy-Young, manager of the farm La Petite Ferme, said the animals were particularly fond of Chardonnay grapes.

"They can easily wipe out up to 2t of grapes a week when you're not watching, and that makes about 1500 to 2000 bottles of wine."

Dendy-Young said he lost up to 40% of his harvest last month to the baboons.

But, on the bright side, Dendy-Young said the thieving was taking farmers back to the traditional ways of French wine making.

"The grapes left on the vine become the tastiest because there is more nutrition from the vines going into those berries, giving the wine intense flavours. When they pluck those grapes, what you're left with then becomes quality. In some parts of France, they would let you yield only a small amount ... the baboons are doing it naturally for us."