Interesting topic, MS. At first, I thought this dissolved oxygen issue was settled and for home brewers there was relief because a)Hot Side Aeration (Oxidation) is a myth and b) there is not much one can do without going to extremes.
I read the referenced
paper It is clear to me that they are primarily concerned with Helles and Bavarian brews (lagers), the most sensitive to oxygen’s influence. Extrapolation to ales is assumed, not proven. I also read the links you provided. The first article has some things that are not exactly correct, especially, “A no-sparge mash would avoid potential aeration from sparging, but lower potential mash efficiency.” We know that is wrong and there is no mention of water volume or time for mashing to make it seem right. You may have seen posts about it on the forum
here and
here.
The pdf proposes using sodium metabisulfite (SMB) to adjust dissolved oxygen levels to below 1 ppm, or down to 0.5 ppm, without having to use a closed system. Dissolved oxygen (DO) levels get lower as the water temperature rises and they are decreased as other dissolved things increase. With 5 ppm as a starting point for untreated real world dough-in, their claim that it is detrimental may have some validity for Helles lagers. They add a reducing agent, SMB, before grains are added in the mash step to get the DO down.
Yes, but… For the lighter flavored beers they are making, adjusting the DO below 1 ppm might have a positive effect, but they give subjective interpretations of flavor as their mark of success. I would like to see analyses that measure aldehydes (i.e. some flavors subject to oxidation) with SMB and without it. Also, they are adding a reducing agent to a complex mixture and it may be reacting with components other than just oxygen. Note that the SMB levels they add are slightly in excess of the DO measured. Excess SMB can do more, perhaps even create the enhanced flavors they mention.
They did not seem to have investigated the closed system they mention. You may not need a
fully closed system to lower the oxygen level while avoiding the addition of SMB. I think that would be a better test. If one bubbled nitrogen or carbon dioxide through hot strike water for a few minutes, DO would be gone by displacement. Adding grist blanketed with CO2 while continuing the bubbles in the strike water would probably work to keep DO low enough for comparison. One could keep bubbling through the mash, even during the boil (boosting the evaporation rate). Then we might find that SMB is not necessary or it creates new flavors. Of course, they seem to say that all the good stuff would be transported away as volatiles and this wouldn't work (Ha!). I no longer have access to all the neat tools that I would use to check this out. I would rather go brew another ale and not be concerned about 5 ppm of DO.
And for anybody using BIAB to make Helles bock, good luck. If you find lowering DO helps let us know.