A 50 year old man died of internal burns when he was served cleaning fluid instead of wine in a bar in Benicarló in the northern part of the Valencian region last Sunday.
It appears the soapy fluid was stored in a wine bottle, and then accidently put in the fridge by accident.
Emergency services rushed him to hospital where he later died.
The Guardia Civil is investigating to see if anybody could be held criminally responsible for manslaughter.
The bar owner was arrested before being released, pending further enquiries.