Without feeding the muscles right after you have worked them, you are essentially depriving them of the nutrients they would normally use to build themselves back up after just being broken down during the workout.
If those nutrients are not there, you will not build new muscle tissue nearly as effectively as you could be.
That said, not all post-workout protein shakes are created equally. Here is what yours should have in order to build muscle as quickly as possible.Whey Protein Isolate
Isolate protein powder is a form that is going to be digested most rapidly in the body and as such, will get into those tissues that need it right now.
Be sure to look for this specific kind when you are purchasing your protein powder, rather than just getting a generic whey.
Aim to take in about 20-30 grams of protein both before and after your workout. About an hour later, you'll want to follow this up with another dose of 20-30 grams of protein in the form of solid food.
Next up, you're going to need to supply your body with the energy it needs to repair the muscles and build new muscle tissue. This will come from fast acting carbohydrates.
Ideally you want the carbohydrates in your post-workout shake to increase insulin levels so that they are immediately taken from the blood stream and directed into the muscle cells.
Dextrose is the choice of many here, as this is easily mixed right into the shake. If you'd like another source of carbohydrates, one that's slightly slower acting along with it, I'd suggest also mixing in some raw oats.
The texture may take a little while to get use to but this is a terrific source of energy for your body.
Aim to eat at minimum, 5 grams of carbohydrates for every two sets of lifting you do. Ideally you will want to take in more than this though, as that will be what prompts your muscles to grow.