Two water samples from the sewage system of the Warsteiner brewery suggest the Legionnaires bacteria has been found.
The environment ministry in the state of North Rhine Westphalia is now probing whether the bacteria has got into the water supply of the brewery in the town of Warstein, or if it is just in the sewage system.
Public health officials also need to discover whether the bacteria found in the sewage system was spread through the air or whether the brewery's water source has been contaminated. Results are expected on Friday.
A spokesman for the environment ministry said the beer had not been affected as it was produced in a sealed area and water is heated to almost 100C during the brewing process. The Legionnaires bacteria die at 60C.
A spokesman for Warsteiner stressed that the beer was safe to drink. "Our production process is safe," the brewery said. The brewery added it was doing everything to protect the health of their employees.
The Legionnaires outbreak in North Rhine Westfalia has affected 165 people with ten needing intensive treatment, including people in the town of Warstein, newspaper the WAZ reported.