Recirculation (vorlauf)
Term from the Brauwerkstatt brewing glossary, category “Brewing and equipment”.
Explanation
At the start of lautering the wort is cloudy because husk particles and flour run out with it. You catch this cloudy wort and pour it gently back on top of the grain bed until the wort runs clear. In all-in-one systems the pump recirculates the wort continuously during the mash.