HERMS Mashng - Grain bed under water

New to HERMS. When I am mashing, I assume I need to keep the grain bed under water while recirculating? Add the stike water and then a little more to keep up with the absorbtion in the grain?

I currently fly sparge, if I switch to batch to control ph issues, then I just need to calculate absorbtion amount and add enough water to obtain pre boil level?

Yeah, you want to keep the grain bed completely submerged during the circulating mash time. I use about 1.5 qt of water per pound of grain for the mash. In my round cooler, I have a few inches of liquid above the grain bed.

As for the batch sparging question....

When your mash is over and you drain/pump the wort into the kettle, the grain will already have absorbed all the water it is going to absorb. So, what you can do is just measure how much liquid you collected from the 1st runnings and subtract that amount from the pre-boil volume target is.

That will directly tell you how much sparge water you have to put in. No more absorption, so everything you put in for the sparge will come back out to the kettle.

Thanks. When batch sparging, do you recirculate your second batch of sparge water before draining into the boil kettle, or do you add the water and go?

After adding the sparge water, I stir the mash up well, and then I circulate it for a while until the grain bed settles and the liquid clears up, then I send it to the kettle. I basically just use the pump as a vorlauf to get the grain bits out of the way and keep the wort going into my kettle very very clear.