For cell expansion, E. coli cells are grown in EB™, while the production of the recombinant protein is almost completely repressed. For high level protein expression, the expanded cell culture is simply added into OB™ media. By using the Dual Media Set™ system, protein overexpression can be reliably controlled for many proteins. In some circumstances, such as when expressing toxic proteins, or when the expressed protein is poorly soluble, over-expression is counterproductive. In such cases, limited protein production can be initiated by adding the specific inducer (IPTG for lac-based promoters) to cells growing in EB™.