ABIDJAN, Aug 18 (Reuters) - Ivory Coast's cocoa grind dropped 31.2% year-on-year in July to 39,301 metric tons, data from exporters' association GEPEX showed on Monday, with grinders citing poor bean quality and low volumes of the mid-crop.

The total grind - part of the process of transforming cocoa beans into chocolate - from the start of the 2024/25 season in October until the end of July stood at 515,055 tons of beans, down 4% from the same period last season.

"July's grinding has fallen dramatically this year compared to last year, mainly due to the quality of the beans," the director of an international grinding company based in San Pedro told Reuters.

"They are mediocre this year, so we are rejecting a large quantity due to a lack of fat and a high acidity level."

Between April 1 and August 17, cocoa bean arrivals at Ivory Coast's two main ports of Abidjan and San Pedro reached only 350,000 tons, down 30% from around 500,000 tons during the same period of last year, exporters said.

Exporters also said grinders have no stocks left and that they will have to rebuild them in order to return to the average grinding rate during the main harvest.

"We are waiting for October to get good beans to rebuild all our stocks and return to the grinding level for the period, i.e. just over 58,000 tons per month," the director of a grinding company based in Abidjan told Reuters.

"This will require us to be aggressive in our purchasing from the start of the season."

The GEPEX data covers six of the largest grinding companies, including Barry Callebaut BARN.S, Olam OLAG.SI and Cargill Inc CARG.UL.

Ivory Coast has a total grinding capacity of around 750,000 tons. It is the world's top cocoa producer and vies with the Netherlands for the leading spot for grinding.

(Reporting by Ange Aboa; Editing by Anait Miridzhanian and Jan Harvey)

((Anait.Miridzhanian@thomsonreuters.com;))