This is to ramp the temperature up to 75°C (167°F) in brewery beer brewing process. This denatures the enzymes and prepares the grain for sparging. the wort is typically recirculated at this temperature for 10 minutes...

A black sludge on the inside of fermenter is normal. The sludge is oxidised hop proteins that often appear as a dark brown/black sediment on the sides of the fermenter at or just above the wort level....

After the mash is complete, the next step in the brewing process is to separate your sugar-rich wort from the leftover spent (ie used) grains. To do this, the grains must be strained away from the wort, and rinsed....