A method for cleaning used beer kegs employing an aqueous solution of phosphoric acid, nitric acid and one or more surfactants, e.g., a detergent and/or wetting agent. Preferably, the aqueous cleaning solution has a total nitric acid content of 12 wt % or less. Complete cleaning can be achieved without using any caustic. The cleaning solution can be recycled repeatedly to clean multiple kegs on numerous occasions over a period of time, e.g., several weeks.