The increase the titer can be as follows: after complete reproduction of the virus, and the manifestation of cytopathogenic effect, until the affected monolayer of cells has come down, you can remove some of the culture medium. Then pass all the procedures for extracting the virus from the cells.

You should use Vitamin C.

thanks Efimova and Muthanna. But what did u mean by using vit c?

I doubt that vitamin C will help to increase the titer of the virus. before freezing the infected cells, they can be precipitated on a 3000-5000 g centrifuge and resuspended in a small volume of medium, then destroying the cells to extract the virus. Sorry, for bad english.

Iagree with M. A. Efimova ,very good informations to slove your problem