The present invention relates to a method for producing phytase variants which has at least 74% identity to a phytase derived from Citrobacter braakii and comprises at least two additional disulfide bonds as compared to this phytase. These phytase variants have modified, preferably improved, properties, such as thermostability, temperature profile, pH profile, specific activity, performance in animal feed, reduced protease sensitiliby, and/or an modified glycosylation pattern. The invention also relates to the variants produced, DNA encoding these phytases, methods of their production, as well as the use thereof, e.g., in animal feed and animal feed additives.