It never does. 'Packaged' blood is still stale as long as it's not fresh from a body, and you can never get the proper nutrients from it.

Listen, I'm sure drinking from a live source isn't the most appealing, but you can drink from me, if you'd like. It'll allow you to get the food you need without hurting strangers or people you love. Additionally, I'm a True Blood vampire, you'll get more energy longer from my blood than you would from humans.