Chicken and beef cuts of meat can safely marinate for 24 to 48 hours before spoiling. Fish should not be marinated for more than 1 hour.
Using marinades results in a more tender piece of meat. The ingredients in the marinades are also absorbed by the meat and provide enhanced flavor.
If marinades are highly acidic, the amount of time the meat needs to soak should be reduced. Leaving the meat in acidic ingredients for too long can toughen the meat.
Leftover marinade should not be used unless it is boiled first. Boiling the marinade destroys any bacteria left behind from the raw meat.