PARIS — Winemakers in the Beaujolais region have been accused of illegally adding sugar to fortify their wines or increase volume.

Police suspect up to 100 growers or cooperative members of purchasing almost 600 tons of sugar and using it to raise alcohol levels above official limits. They are also suspected of exceeding wine volume quotas and selling the extra bottles on the black market.

The investigation is the latest blow to the region — hit by a recent scandal involving mixing wines and accusations of favoring quantity over quality.

Police arrested four people earlier this month who reportedly acknowledged having transported and sold the sugar in northern Beaujolais between 2004 and 2006. The area — encompassing northern Rhone and southern Saone-et-Loire — is home to more than 2,500 wine producers and 12 different appellations.

Police suspect winemakers of not mentioning the “invisible” sugar supplies in their carefully monitored records on “chaptalization” — adding sugar to unfermented wine musts. Chaptalization has been used since the 18th century, but there are strict limits to how much sugar can be added. Others may have used the sugar to increase volume and feed excess wine into a “parallel” market to circumvent quotas. Until now the probe has focused on those providing the sugar but has now moved on to the winemakers.

The first discovery in the case was made three years ago, during the 2004 harvest, but it may have been taking place as early as 1998 and continued up to 2006.

The inquiry could put into question all the 2004 and 2005 vintages of the producers implicated.

Ghislain de Longevialle, the head of Inter Beaujolais, the region’s winegrowers and traders body, condemned any “illegal practices” and said his organization could file for charges against a “small minority” who tainted the region’s reputation.

“This is the last thing we need, as it threatens to overshadow all our efforts to reduce volume and improve quality over the past 10 years,” he said.

Last year, the French wine producer credited with transforming Beaujolais Nouveau into a global phenomenon was found guilty of mixing low-grade wine with top vintages.

Georges Duboeuf, 72, the self-styled “King of Beaujolais,” was convicted of “fraud and attempted fraud concerning the origin and quality of wines” and fined 20,000 pounds.