After some research, I’m having some trouble grasping the concept of this chart. It would seem to me that the mash 1st runnings gravity reading would be dependent on the amount of grain in the mash vs the mash grist ratio. I would like to take a gravity reading during the RIMS process to see when the conversion is done. Is this chart correct or is there a better equation to predict the gravity reading?
Yes, the chart is generally correct. The chart is a little inaccurate if you use 6-row because there is less starch in 6-row.
The amount of the total mash wouldn’t matter, just the ratio. For example, if I made a mash with 1lb of grain and 1.5qt of water, I should run off about 1.080 (1.5qt/lb). If instead I did 10 times that, so 10lb of grain and 15qt of water, I should get the same thing since the ratio is the same.
Maybe think of it like you have a fixed amount of sugar, and you are diluting it in varying amounts of water. That isn’t exactly true since I think the extraction rate changes with the grain/water ratio, but as a conceptual tool I think it works. So, if you dilute 40 gravity points of sugar (about a pound) in 4qt, your runnings would be 1.040. If you instead used 2qts, your runnings would be 1.080. Same amount of sugar, just less diluted.
Sorry if that wasn’t helpful at all.
The chart should work pretty well. If you want to plug in some different assumptions I have a calculator that’s a little more flexible: Batchsparge « SeanTerrill.com