How do you properly bring a contract brew through the production system when the raw ingredients were purchased by the contractee?
The best way to do this is to setup a Contract Brewing warehouse, where you can bring into stock normal raw materials, but at $0 if you need to. Then you can have them on BOMs, Prod Orders, etc. and can consume them in production without having them increase the value of the beer.
This works because OBeer inventory costing is "at the warehouse level", which means that the system holds costs separately at each warehouse, and the cost applied to the item being produced comes from the cost of the raw materials in the specific warehouse they are consumed from.
Once you create the warehouse, you'll need to add it to each item that needs to be in that warehouse.
Then, if you have BOMs specific to those contract brews, you can setup the BOM to pull from the Contract Brew warehouse, instead of your normal warehouse.
This setup helps keep inventory separate between your inventory and the inventory purchased by the contractee.