Why do you have to throw away baby formula after one hour?

That is to ensure your baby doesn't get any bacteria that may have formed in the milk after you have begun feeding for a time. In the hospital the regulations are stricter and they tell you to throw it away after 30 minutes, at home the environment is different so after one hour, all used formulas that have touched the baby's mouth will need to be discarded.

If you prepare the formula using powder, you can store it in the fridge up to 24 hours.

If you use the pre-made formulas in the cans, you can store it up to 48 hours.

You should never freeze formulas also.