Following the incident, the coffee was sent for testing. The police confirmed that the narcotic had been identified, yet kept silent about exactly what substance had been found in the coffee.
"At some point we will of course tell, but because of the ongoing investigation we will not yet say," lead investigator and senior criminal officer Seppo Leinonen said.
At present, Finnish police are considering charges relating to assault and drug offences.
"We have checked who was present when the obvious exposure took place. Currently we are investigating the people's backgrounds and doing other analysis work to determine who has put the substance in the coffee," Leinonen said.
All of the workers affected were middle-aged men, and all were hospitalized for treatment. The case was described as "highly unusual."
"I have been a criminal investigator with the Savonlinna police for 14 years and I don't remember any other similar case," Leinonen told Yle.
Finnish people are the world's most voracious coffee-drinkers. According to statistics, one of every hundred coffee beans is exported to Finland. The Nordic nation's total yearly consumption tops 12 kilograms per capita, more than Norway, Iceland, Denmark or Sweden.