My normal protocols are Yeast Oxygen Scavenging (YOS) and adding 1.8 grams Trifecta per 10 gallons of strike water.
The YOS treatment gets done the night before brew day, and supposedly will continue to reduce dissolved O2 to “barely measurable levels” for several days, or until it gets denatured early in the mash.
The Trifecta gets added with the brewing salts and calculated acidification just prior to mash in. It’s been so successful for me that I no longer bother with underletting the strike water. There’s no D.O. in the strike water, and the Trifecta takes care or any O2 pickup during the actual mashing.
In the two years I’ve been doing this, my beers have shown amazing shelf life, though hoppy beers still tend to fade a bit with time. But staling of the beer and its associated off-tastes get held off for months. It’s been a while since I’ve had a ‘dumper’ due to sherry-like or ‘wet cardboard’ from an older beer.
I tend to brew mostly lighter ales and Continental lagers, which tend to not age gracefully and leave no cover for flaws. Off-flavors from oxygen staling would be easily noticeable.