I’ve been trying to find info on the timing and dosage of PMB/SMB, Brewtan and ascorbic acid for oxygen scavenging. PMB/SMB is added to the mash water if I am not mistaken. Brewtan is added to the mash and late in the boil in dosages of 1/4 and 1/2 tsp respectively for 5 gal, also if I am not mistaken. What about the ascorbic acid? How much and when?
I have reviewed the stoichiometry of chemical and biologic deaeration and found that deaerating strike and sparging water via yeast scavenging is a wise approach. That is due to the oxygen load from the supply water being the largest dose that the mash and wort incur and using yeast scavenging effectively reduces the need for chemical scavengers. However, we still need to apply a prophylactic dose of any of those chemical scavengers to protect during mashing and boiling processes.
If I’m adding Sodium Metabisulfite to address chloramine in my tap water, do I want to do that before or after yeast scavenging? For yeast scavenging, just use something like bread yeast and table sugar? Amounts?
SMB or KMB additions should be dosed AFTER the yeast scavenging process, to avoid consuming that prophylactic dose. If your mashing methods are fairly air-tight (mash capped, not stirring the mash, etc), then the size of the prophylactic dose can be pretty small.
de-aerate with 1 gram per gallon each active dry (bread) yeast and (table) sugar heated to 114°F for 20+ min. The yeast will consume the sugar and all the O2 in the water. This can be done the day prior to brewday. The water will maintain zero O2 for several days. After 20+ min continue to heat water to strike temp.