How long does beef stay fresh when marinating?

Answer 1

In a covered container in a cold fridge, covered in marinade, depending on the marinade anywhere from 3 days to over a week, as long as it is stirred.

It seems to be an oxymoron to call marinated beef 'fresh'. Depending upon the marinade, it could be adding acid, salt and/or sugar which could have some preservative properties that might allow for a longer shelf life compared to non-marinated beef.

Use a recipe from a trusted source and don't push the time table to it's limits.

Answer 2

Up to 7 days, so long as it has not exceeded it use-by, and is kept refrigerated at all times during the marinading process. (Although somewhere around 4-5 days it's probably better to at least drain the marinade off, even if you intend to cook the beef in another 2-3 days. If the marinade is very acid the beef could become an odd texture if it's left in there for the full 7.)

It also depends on the keeping qualities of the marinade - if it's yogurt based (such as in some curry dishes), 3 days is the maximum (so long as the yogurt is not out of date before then).