Up until now ive only followed recipes. I have done a number of extract brews and partial mashes. Im looking to get started with all grain at this point. While looking at the recipes i was curious as to how they come up with the grain bills. I have a decent understanding on pitching rates and hop utilization, etc. But as of right now i have no clue as to how to figure out what grains to use or how much to use to hit a target OG. Any help?