A fresh freezing medium assured you a clean culture. Personnaly I don't use medium that have more than 2 weeks.

For freezing, I use a 90% FBS- 10% DMSO solution. Easy and rapid to make !

I use 50%FBS, 40% DMEM and 10% DMSO.

Thank you for your response, i should hence throw the freezing media.

thank you Antonio, that would help

Antonio has good advice. Fresh is best...