mkarnas said:
I wanted an understanding of why some instructions tell you to sparge until you get to your volume. That would just dilute the wort and thus lower OG.
Those kind of instructions are intended for people who fly sparge, which is really just continually rinsing the grains (as opposed to batch sparging, where you use specific volumes of water and stir it to dissolve all the sugars at once). Because of this, it won't dilute the wort if you fly sparge.
mkarnas said:
Here's another way of looking at my question. How much water should you sparge?
If you batch sparge (or even no sparge) , you need to calculate how much water is needed, which depends mainly on 1) the "dead space" in your system, which is the volume of water that remains on the bottom of your mash tun, in the hoses, etc (i.e. the volume that doesn't make it to the boil kettle when you dry run your system without any grain at all) and 2) how much grain is being used, because the grain absorbs some of water.
Because of the first factor, the amount of water needed to sparge varies from brewery to brewery, which is largely why it isn't typically included in recipes. And because of the second factor, it needs to be calculated for every recipe. Brewing software will simplify this for you, by automatically calculating how much water is needed based on your brewery profile, the amount of grain used in the recipe, as well as things like the mash water/grain ratio and the number of batch sparges you desire. And software allows you to constantly tweak all aspects of your recipe and preferences without having to do all the calculations every single time - they are automatically updated every time you make a change. It really is such an invaluable tool in the modern brewer's toolbox.