The sparge process is simply rinsing sugars and proteins from the grain bed and moving your wort (sugary liquid) from the Mash/Lauter Tun into the boil kettle. It is at this point in the brewing process that the brewer tries to collect as much fermentable sugar as possible to achieve his/her target gravity. Gravity is simply the density of your wort with sugar and proteins. Many brewers will check gravity readings at the end of the sparge process, prior to pitching yeast in the fermenter and at points throughout the fermentation process. The goal is to understand, did we extract the right amount of sugars from the grain bed, and was the yeast healthy enough to consume enough of the sugars to provide the right alcohol by volume?
Before starting the sparge process, the brewer will ramp the Hot Liquor Tank (HLT) water up to 172°F and ramp the Mast Tun to roughly 166°F. There are two reasons for this. First, 166°F stops the enzymes from trying to convert starches into fermentable sugar and freezes your wort at a specific gravity. Second, 172°F rinse water helps thin out the sticky sugars and separate it from the grains. It is crucial that you don’t let your sparge water get higher than 172°F or you will extract tannins from the grain husks. The last important part is to calculate how much water from the HLT is needed to rinse the grain bed and transfer the right volume of wort into the boil kettle. Here is how the sparge process works in pictures on a 2 Barrel electric brewing system at the Fainting Goat Brewery.
Last and final step is not pictured but is hugely important. I keep an eye on the sight glass on the HLT and once the water level drops to the mark needed, I immediately shut off the HLT pump. At this point, we have the exact amount of water needed in the Mash Tun to rinse the sugars from the grain bed.