I have long been intrigued by this old method, but have never gotten around to attempting it. Back in the 1850s, during the period that English beers were hopped to the point of being silly… this process was developed as a means of getting more hop presence in beer than could be achieved by adding to the boil, or by dry hopping (most English hop varieties don’t dry hop well anyway).
Unlike FWH or mash hopping, this process is carried out independently.
Hops, typically one ounce per pint of water, were placed in water at 160 degrees. Six hours later, the water was added to the wort, sometimes at the beginning of the boil, mostly at the end of the boil.

To do this, say for a 5-gallon batch…. Calculate gravity based on a five gallon batch. Then decrease the strike and sparge water until the post boil volume is 4.5 gallons. Add hops aggressively during the boil as normal.
Six hours before the end of the boil, pre-heat your oven to 160. Heat ¾ gallon of water to 165 or so… and add 8 ounces of hops (whole, no pellets) Heat on the stove gently until you get to 160 degrees, put a lid on it and stick in the oven.
After six hours, pull out the pot, drain off the liquid and squeeze the hops until you get a half gallon. Add this to your wort at the end of the boil.

I have absolutely no freaking clue how to calculate IBUs for this….. But, if FWH, for the short time the hops are steeped, increases hop flavor, and adds a smooth bitterness….. I can only guess what SIX HOURS of this would do…
I believe that this would really, really, really lend itself well to a big, intensely hoppy American IPA…..
Anybody care to give it a try??? Say with Citra???? @frydogbrews ????