Regarding capping on foam, off the AA topic a bit. I'm using a counter pressure bottle filler ( williams warn type), it's a closed transfer from the keg to the purged bottle. You fill to the top from the bottom and it vents the bottle of CO2 to balance the pressure so no excess foaming and then when you take the bottle off the volume displaced by the filling straw means the headspace is left. Because the beer is carbonated it will bubble up slowly and fill that headspace to the top with foam or I just give the bottle a jiggle and when the foam rises I then cap on it. In the meantime I've already got the next bottle filling. It works really well and is a non messy procedure.
Getting back to AA I came across this paper
Chemical Stability of Ascorbic Acid Integrated into Commercial Products: A Review on Bioactivity and Delivery Technology published January this year so up to date.
" Ascorbic acid is also used as an antioxidant to protect the sensory and nutritional properties of foods. As an anti-browning agent, it can inhibit the browning of vegetables and fruits caused by oxidation. The formation of quinones mediated by polyphenol oxidase causes the accumulation of H2O2, which in turn causes the browning of polyphenols mediated by peroxidase [
25]. Ascorbic acid inhibits browning by reducing the o-quinone produced by polyphenol oxidase to the original diphenol through a process called “deactivation reaction” [
26]. In addition to the regeneration mechanism of polyphenols, the protective effect is also attributed to the competitive inhibition of polyphenol oxidase activity by ascorbic acid. Meanwhile, addition of ascorbic acid causes a decrease in pH and is not conducive to the expression of polyphenol oxidase activity [
27]."
same paper re temperature
" The degradation or oxidation products of ascorbic acid heated at 100 °C for 2 h include furfural, 2-furoic acid, 3-hydroxy-2-pyrone and an unknown compound. Among them, furfural is one of the main degradation products of ascorbic acid, which can polymerize or combine with amino acids to form brown melanoids, causing the browning of ascorbic acid-containing juice products [
62]. Furthermore, thermally oxidized ascorbic acid was identified as a potential precursor of furan; it is a possible carcinogen usually produced in some heated food products [
71]. "
So I'm not sure how a one hour boil can see any residue carried over that's of benefit. Some of the above products are made below 100C and so will be forming during the mash.
But oxidation definitely makes NEIPA go brown so adding it later may be of benefit. Whether the prooxidative actions mentioned in the paper because of metal ions can be promoted the Mg and Ca ions I'm not sure, but Fe and Cu are implicated.