Michelle, the guys have a good point about re-using brine, but it doesn't sound like that's what you're doing. A freshly-made brine should actually last quite awhile in the fridge without issues. It's essentially preserved with the salt in it, and really nothing to "spoil," if kept around 40° in the fridge. Just don't add any fresh ingredients (chopped garlic, onions, orange slices, etc.) until ready to take the meat for a swim!