Maintaining Volume of the Batch

I have not yet tried all-grain brewing, but as I have done a few extract batches I am ready to take the next step. Thru all of my reading and research on the subject though, I still have one question that remains unanswered. How does the volume of the batch get maintained? - I.E. If you are making a 5 gallon batch how do you maintain you end up with 5 gallons? I have not read anywhere any instruction on adding water to the fermenter to bring the btach up to 5 gallons as in extract brewing.

First off, you'll make everything a lot easier if you're doing full volume boils. Then you just set up assumptions for grain absorption, boil off, etc. By far the easiest way is to use brewing software like Beersmith. Just plug in what you want your batch to be and the equipment you're using and it will spit out the volumes of water you need based on some preset assumptions. If you find that those assumptions aren't quite accurate for your setup, you can always tweak them.

The basic idea in most AG brewing is to use specific quantities of water in your mash (when you soak your grains in water at a specific temp to convert the starches in the grains to sugars) and your sparge (when you rinse the grains to remove as much of the sugars as possible into the kettle) to achieve a volume that will boil down into 5 gallons, or whatever final volume you're shooting for.

The exact volumes you will use depend on a lot of variables, including but not limited to:
-the water-grain ratio you want in your mash
-the temp you'll be mashing at
-how many steps you'll use and whether you raise temp by infusion or not
-what kind of sparging technique you use (if any)
-how long your boil is
-what your boil-off rate is
-how much loss you expect (due to mashtun design, grain absorption, etc)

Brewing software is probably the easiest way to streamline these variables as most of the relationships are modeled and all you need to do is enter your parameters. I use both Brewsmith and Hopville.com (which is free and easy for quick recipe mockups and calculations), others have their favorites. But either way, it's good to understand what the computer is calculating, even if you're not running the formulas yourself. If you don't have a basic brew book like Palmer's How to Brew or Papazian's Joy of Homebrewing, they give good overviews of the AG process that should get you started. If you have other questions, there's a wealth of knowledge on this site.

Cheers

@Jerrodm

Exactly what I'm trying to do. I want to understand why the computer spits out and calculates its information when formulating a recipe. I do have the Palmer book, but he doesn't get into water quantities.

Ah OK. Well if you want the specific equations, I would look at the partigyle/batch sparge calculator on BrauKaiser's website. It's an excel spreadsheet that has formulas for a lot of the things that the software packages calculate for you: water temp/volumes for mashes, water absorption, boil off rates, etc. It's not too complex, it's a little like watching an engine run with the hood open. And you can input different variables and see how it impacts your final volumes, efficiencies, etc. The link is here.

Hope that's helpful.