AN attempt to extort $500,000 from a drinks manufacturer by threatening to poison its product ended in a six-year jail sentence for 31-year-old Chen Chun-man. A High Court jury found him guilty after hearing that in September 1991 he had telephoned the Yakult company in Kwun Tong several times demanding $500,000, and saying he would ''add something'' to the firm's drinks if he was not paid. Police were notified and negotiated with him. One officer was told that if the money was not paid, an advertisement would be put in newspapers that Yakult drinks had been poisoned. That call was traced to a restaurant in Tsing Yi, and when Chen left, he was arrested. The phone number of the Yakult company was found in Chen's flat. In mitigation, Mr Stephen Franklin said no violence was used, no one was harmed and there was no evidence that Chen would have carried out his threat. He said Chen was not a professional extortionist and the amateurish plot was doomed to failure from the beginning. Passing sentence, Mr Justice Leong said blackmail was a despicable offence. Chen was blackmailing a large company, whose product was consumed by many. His threats would have alarmed the public, the judge said.