sparge

What exactly is sparging and when is it necessary?

Sparging is basically rinsing your mash, to extract more sugars from the grains. I would think it's always necessary in AG brewing, if only to try to maximize efficiency. There are multiple techniques, but I am only familiar with batch sparging. Here, you heat water to 170*F (the amount is determined by your recipe, somewhere in the neighborhood of 40-60% of your preboil volume). Someone else would have to fill you in on the other techniques as I have no experience with them.

sparging is only done in all grain brewing. first you mash to extract sugar from the grain, then you rinse the grain with hot water to get as much sugar out as possible.

i had terrible results with batch sparging. i was getting less than 50% efficiency. you should get 70% to 80% efficiency if you are doing it correctly.

so, i built a 3 tier rack so that i could fly sparge. the sparge water pot on the top, the mash tun in the middle, and the boil pot is on the bottom. now i get 75% efficiency.

fly sparging means that you start running the sparge water into the mash tun while the mash water is running out of the tun.