Thanks for the replies. Instead of starting a new thread, I have a couple other questions in the same realm.
What is the relationship between grain amounts vs OG vs volume of water?
At a consistent mash temp temperature, as grain amounts go up does OG go up or does it depend on the volume of water used?
There is a fixed amount of sugar available in a fixed amount of grain. But the sugar starts out as starch, which must be converted into sugar. The percentage of starch that you convert into sugar is your conversion efficiency, which can reach 100%, but is often less. The biggest factors affecting conversion efficiency are mash time, mash temp, and crush fineness. Mash thickness and pH are secondary factors in conversion efficiency.
The SG in the mash will depend on the conversion efficiency and the grain to water ratio. The more water, the lower the SG. The lower the conversion efficiency, the lower the SG.
The next factor is lauter efficiency. This is the percentage of the sugar actually created in the mash that makes it into your boil kettle. Lauter efficiency is alway less than 100%, because you just can't rinse all of the sugar out of the grains (without using an infinite amount of water.) Lauter efficiency drops as the grain bill weight increases for a fixed batch size. This is because more grain will retain a larger fraction of the wort volume, and the retained wort contains a significant amount of the created sugar. Sparging methods have the largest effect on the lauter efficiency, with no-sparge having the lowest efficiency, batch sparging higher efficiency (with more sparge steps giving incremental improvements), and continuous (or fly) sparging having the potential for greatest lauter efficiency. However, a poorly conducted fly sparge can have terrible efficiency. Lauter efficiency is also greatly affected by the grain absorption rate. Lowering the absorption rate (by squeezing for example) will increase the lauter efficiency. Undrainable wort volume in the MLT will also lower lauter efficiency.
Your mash (or pre-boil) efficiency is equal to conversion efficiency times lauter efficiency. If your conversion efficiency is essentially 100% then mash efficiency equals lauter efficiency.
So, there is no simple relationship between grain bill weight, water amount, and OG, unless you know your typical conversion efficiency, and lauter efficiency, and these are different for everybody's processes.
It is possible to measure both conversion efficiency and lauter efficiency, and it's possible to simulate lauter efficiency for no-sparge and batch sparge processes (fly sparging is way complicated.) The chart below shows how lauter efficiency is affected by sparge process, grain absorption rate, and grain to total brewing water ratio.
Brew on