I must confess I do none of these, though some, such as underletting, seem quite feasible with my current system. However, the "Low vigor boil" concerns me. I thought the point of boiling (besides sterilization, alpha-acid conversion, Maillard reactions, yada, yada) was to drive off DMS, and that the vigor of the boil, its length in time, and even foam production (see
Janish's excellent article) accomplished this.
After some idle speculation, one idea is a CO₂ injection in the boil. I am by no means suggesting the creation of a "CO₂ blanket" on the surface of the wort to protect it from oxygen. Instead, picture what is going on in a normal boil. The bubbles popping at the surface are mostly water vapor, and because these bubbles are hotter than the ambient air and water molecules are lighter than the two main components of air, O₂ and N₂, the water vapor is considerably less dense than surroundings and rises rapidly. Like a miniature nuclear mushroom cloud, the rising water vapor pulls a vortex ring of air underneath it, dragging oxygen down to the wort surface. In a nutshell, oxidation in a normal boil comes from water-vapor-induced turbulent mixing of the air above the kettle.
With CO₂ injection, each bubble would have a mix of CO₂ and H₂O that would make the average molecular weight closer to that of ambient air. The gas from the emerging bubble would rise at a more stately rate, leading to a weaker vortex ring and less down-movement of air. Slower rise would allow for more horizontal mixing of adjacent bubbles into a joined mass of CO₂/H₂O, filling more of the volume of the above-wort portion of the kettle. A dense, collimated column of slower moving CO₂/H₂O would push its way out of the kettle, allowing for less oxygen infiltration.
I can think of a lot of downsides, including the expense of the CO₂ (unless you've been capturing your own and don't know what to do with it all?), and that the expanded CO₂ will be cold and will eat some of the heat from your burner. Might want a longer length of hose to allow ambient air to warm it up, but make sure you don't melt that hose. I imagine you'd direct it through a stainless steel spike down to the bottom of the kettle (no air stone, that would foul up instantly, or perhaps even disintegrate).
Alas, McMullan, I have no data, just a thought experiment. I'd be curious to know if someone has tried this before.
