They believe professionals were at work and could strike again.
Red pinot noir and white chasselas grapes are the most common varieties grown in Switzerland.
According to newspaper reports, thieves broke into a vineyard near Ins in the Bernese Seeland district at the end of September.
Winegrower Lorenz Hämmerli said the protective nets covering his pinot noir vines had been cut at the sides.
The brazen thieves had simply picked the chasselas grapes from the vines along the roadside, Hämmerli said.
He said several people had probably been involved.
A neighbour noticed torchlight coming from the vineyard at 3am on the night of September 23rd, but believing it was the vintner himself checking on the crops, did not alert the police.
Although the grapes make up just a small percentage of Hämmerli's total stock, he is angry at the loss, having put a lot of work into ensuring a good crop of grapes.
Swiss winegrowers have had a difficult year, with frost and hail destroying crops in some places.
A spokesperson for Bern cantonal police said it was the first time a grape theft had been reported in the area, which has about 246 hectares of vines.