What is whirlpooling?
You may hear the term whirlpool in discussion by professional brewers and some homebrewers alike.
Whirlpooling is the process of getting the wort in the kettle spinning to generate centrifugal force. Just like being a kid in a pool, once you get the wort spinning enough there is a density gradient created that forces any solids (hops and break material) towards the center of the kettle.
After the whirlpool slows down considerably, the wort can be slowly drawn out of the kettle from the edge where there is the least amount of kettle debris. In some kettles, there may even be a diverter plate installed on the inner-most side of the valve opening to hold back kettle material as the flow of fluid tries to draw it into the draining valve.
What’s the benefit? Clearer wort into the fermentor means less loss to cold-break material and yeast debris in the fermentor. It can also be speculated that clearer wort at this stage improves the chances of clearer beer in the final package.
How do you do it at home? When I finish my boil, I leave my stainless steel spoon in the kettle to keep it sanitary from the heat. Then I start my chill with an immersion chiller that entered the wort 15 minutes before the boil ended. As the wort chills, I can stir occasionally with the spoon. This leads to more efficient contact of hot wort with the cold coils of the chiller, reducing chilling time. After the wort reaches my chilled temp, I pull out the chiller. Then with the still sanitary spoon in the fermentor, I start to stir in big circles. This creates a very nice whirlpool. I pull the spoon out and put a lid on the kettle to let it spin and slowly stop. Generally, I let it rest for 20 minutes or so while I clean up and prep a fermentor and airlock. When I am ready, draw the clear wort out of the kettle.
Another way that’s slightly more fancier is to use a brewing pump to create the whirlpool. Pulling wort out of a valve at the base of the kettle, then reintroducing a 6-8 inches below the surface and parallel to the surface. This creates a whirlpool using flow rate. If you have the equipment and do this while using an immersion chiller, you get superior chiller-wort contact. (As reported by Jamil Zainasheff).
I hope that helps describe whirlpooling and its applications in clearing wort and chilling wort.