"The substance was originally for industrial use..."
The restaurant was shut down on 25 August and ordered to pay a fine after a salmonella outbreak affected 102 people.
There are 215 confirmed cases of listeriosis on the mainland, principally in Andalusia.
Three people got salmonella poisoning after eating at the restaurant in June.
Of the 91 people affected, nineteen were positive for salmonella.
The large variety of food served at the restaurant has made detecting the precise source quite difficult.