Task:

casein slow digesting protein between meals and night

Not all proteins are created and digested equally.  Different proteins get broken down and absorbed at different rates.  You will use this to your advantage and plan accordingly.

Whey protein isolate is broken down and absorbed very quickly.  This makes it excellent for your post workout shake.  Other than that, you will want be using casein protein.

Casein proteins gel up in the stomach and can take more than twice as long to be broken down into their amino acid sub components by the body.  This trickle of nutrition can give your body the steady stream of nutrients it needs without any spikes and droughts.  Your body does not do a good job of storing protein, so you want this time release to keep your body fueled.

Use casein proteins for your between meal and bedtime shakes if you can't get enough proteins from your normal meal plan.