The optimal time to harvest the protein will depend on the specific properties of the protein being expressed and the selectedExpiCHO expression system protocol.

At the time of harvesting, cell viability should be at least 75% or higher. These values will ensure maximum performance of the ExpiCHO system. If the cell viability decreases during the process and/or it is lower than 75% at the time of harvesting, this indicates that conditions may need to be further optimized to obtain maximum performance.

Having a cell viability of 75% and above indicates that cells were healthy and could make maximal protein. However, it also means that you will find fewer proteases in solution and less cell debris which would lead to easier protein purification procedures.