So let me address a few things here....
BTB is not a thing low oxygen brewers outside this circle really use, we don't really see a need for it. I have many BTB free beers that are just are fresh as the day they were spunded 8 months into kegging. Since we are using yeast and sulfur as our scavengers, there isn't these fenton reactions, so soon.
@Beersk, German recipe literature say 1% max of roastmalz, there really isn't a need for more, but if for some reason you want to, Sinamar is your answer. My last bottle lasted me a year, with no issues.
Make sure and take about 20% off the color when lox oxygen brewing, your old recipes will no longer be the same color. The oxidation browning will not be adding to SRM.
Also be very wary of the CO2 you use, simply force carbing has enough oxygen potential to oxidize a batch by itself. This is why sulfur fades in the keg