Occasionally, insects are detected in beer in the market. When an insect is detected in pasteurized beer, it is now possible to determine whether it entered the beer during the packaging process or in the market by measuring the catalase activity of the insect. However, this method is unreliable when used to analyze unpasteurized beer. A new method has been developed that is suitable for unpasteurized beer. The change in activity of a variety of insect enzymes when an insect is soaked in beer was investigated. A certain degree of cholinesterase and acetyl cholinesterase activity was detected in fresh insects. These activities decreased when the insects were soaked in beer. The length of time the insect had been soaked in beer could be estimated by measuring the residual activity of these insect enzymes.