I did my second batch of AG today. This one was different from the first because it required significantly less grain and volume of water than the first.
I realized a difficulty when I poured water into my kettle to heat the strike water: the thermometer on my kettle was higher than the water level - making the thermometer useless. In an endeavor to get an accurate reading for my strike water, I borrowed volume from what was to be my sparge water, and mashed with a higher volume of water. I could then read the strike water temp easily (although it made reading the smaller remaining sparge water temp very difficult).
With some minor adjustments, I hit my hour long target mash at 152 F. The temp held well for the full 60 mins. Things seemed to go tickity-boo.
I was then to target a volume of 175 F sparge water. However, since I already had more water in the mash than was originally called for, I reduced the volume of sparge water accordingly. So I raised the temps a bit on the sparge water (to about 180f instead of the target 175f) and went and did the sparge.
My OG after the brew nailed the OG targeted by the recipe perfectly (I think I was lucky?).
So my question is this:
What happens in the sparging process that requires a specific volume of higher temp water? What are the trade offs for using more water in the mash with the same grain bill, and still sparging but with less of the recipes recommended volume?
I'm not exceedingly worried about this brew (although maybe I've screwed up in ways I've yet to find out). However, I'm curious as to both the theory and practical results of the strike vs. sparge processs.