When brewers mention a whirlpool addition of hops they are talking about hops, either pellet or whole hops, being added at “flame out” this is after the boil time of your wort. In many cases the presumed temperature is 80c or lower, the point is that you are trying to extract flavour and aroma rather than bitterness. Often you will read that bitterness is only extracted at 80c or above, this is not true however, less bitterness is released at the lower temperature.
Recently we have learnt from Siren Craft Brew that they have practiced whirl-pooling at 87c and this has produced increased dominant fruit flavours. We are experimenting with this method at TMM HQ at the moment.
Whirl-pooling hops has two clear benefits, it increases the amount of soluble compounds released from the hops over simply steeping them. It also concentrates the hops and trub into the centre of the boil kettle. This enables clearer wort to be drained from the side of the kettle.
This second point is very important when it comes to using pellet hops, and believe me, use them once and you wont be using leaf again, the utilisation if far better with pellets. Do bear in mind that since the hops and trub will be concentrated in the centre of the kettle, this is likely the exact spot that your hop filter is picking up from. In this case it is certain that your filter will block within seconds. To successfully use pellet hops it will be necessary to completely remove your hop filter. If using leaf hops it will be safe to use a hop filter but you will need to take it slowly, this is key. The procedure is as follows:-
Allow your wort to cool ( or force cool ) to your desired temperature
with a sanitised spoon / paddle ( leave in the boil for the last 10 minutes ) gently rotate the wort within the kettle so that the whole mass is moving round, it is important that it is the whole mass of wort is moving, not just the top. This will take a minute or so.
Add your charge of hops for the desired amount of time. You may want to get the wort moving again, maybe a couple of times.
Once your hope have had their allotted time, make sure that the wort has completely stopped moving, it is still.
Open the valve on the kettle very gently at first, you do not want to disturb the trub/hop cone that you have built up at this stage.
When the kettle is nearly empty you will be able to see the hop/trub cone. Do not drain too much from the kettle as you want to leave as much of that cone behind as possible.
Whirl-pooling can be successfully carried out as a manual process however, even more utilisation will come from using a pump setup. The idea is that wort is dropped from the kettle valve to a pump, then back from the pump to a whirlpool return. This is normally somewhere above the kettle valve but placed to accommodate the rest of your brewing system. A valve is required on the outlet of the pump, this is used to throttle back the flow. A valves van be mounted to the pump or and in some circumstances, ideally mounted to the kettle. Wort is then directed round the inside of the kettle by using something as simple as a 90 degree elbow and silicone tubing or a dedicated whirlpool valve. Again the key is to start and drain very gently.
Whirlpool hop editions and the use of plate chillers. This is where many brewers fall foul of a blocked chiller. My recommendation is to keep a plate chiller out of the loop when whirl-pooling, add it back in once that trub/hop cone is formed and drain the kettle from the side well away from it.