why we expose SCDA plates for four hours?
It is a regulatory requirement.
Regulatory environment that is why plate exposure time is 4 hours…
to prevent the dehydration of the TSA media in the plate and become less sensitive for Bacterial growth.
SCDA media having dehydration time I.e 4:45hrs maximum.
This medium can growth Bactria and fungi on the surface and call general media
It is regulatory requirement. Apart from regulatory requirement u can validate the plate exposure ( passive monitoring) timing (In house).
Firstly its regulatory requirement, you can expose plates for 2 hrs and replace them with another plates for next 2 hrs . finally you have to calculate CFU/ 4 hrs only.