I've been getting into overnight oats recently, and thinking about getting more protein in them. Some recipes (for example, here) suggest just adding protein powder.
But, at least one manufacturer says this:
Q: Will my protein drink lose potency if I pre-mix ahead of time?
A: Not necessary – but, it will spoil if it’s not stored properly or used too long after it’s prepared. For best results, mix-up no more than a day’s worth of protein at a time, store it in the refrigerator (in a covered container), and use within 2 days of preparation.
I usually make a few days to a week's worth of oats at a time, and not knowing what exactly causes protein powder to "spoil," I'm wondering if protein powder will indeed spoil in overnight oats specifically over up to five days.