Alternate methods for oxygen scavenging mash water

[Bilsch]

Someone said to me, in the context of pitching in oxygenated wort, yeast are the best oxygen scavengers we know. Shortly thereafter, while reading up on calibration of DO meters, I came upon the mention of zero water and the ways to make same. This got me thinking maybe we can harness the wee beasties for more than just turning wort into beer. Possibly they can help us before the mash by cleaning up dissolved O2 in our brewing water and save the time and energy needed for boiling and cooling the strike water. For lack of a better term, let’s call this process yeast oxygen scavenging. To that end, I did several small tests using cheap and available baking yeast for this purpose. It also seemed reasonable to assume that the yeast might need some fuel, beyond their reserved glycogen, to do their job more effectively. Initial tests employed dextrose and subsequent ones DME.

YOS test 1:
450ml RO water @27c in 500 ml erlenmeyer flask with stopper
0.02g MgSO4
0.05g CaCl
0.25g Dextrose
0.2g bread yeast, dry
Initial DO reading- about 6.5 mg/l
1 hour - 0.33mg/l
2 hours - 0.27mg/l
3 hours - 0.31mg/l
5 hours - 0.36 mg/l
17 hours - 0.47 mg/l

It should be noted here that the best DO reduction I could get by boiling alone was 0.48 mg/l and that was under reduced pressure for 1.5 hours.

YOS test 2: (reduce the amount of yeast by ~½ from test 1)
450ml RO water @27c
0.02g MgSO4
0.05g CaCl
.27g/l DME
0.1g bread yeast, dry
Initial DO reading ~6.92 mg/l
6.23ppm @ 6 min
2.29ppm @ 40 min
0.86ppm @ 60 min
0.31ppm @ 104 min
0.44ppm @ 122 min
0.30ppm @ 154 min
0.28ppm @ 213 min

YOS test 3: (test to evaluate the process with no added sugars)
450ml water @ 35c, with same mineral profile as above
0.1 g dry bread yeast
Initial DO reading ~6.52 mg/l
5.41 ppm @ 26 min, 33c
4.25 ppm @ 60 min, 30c
2.73 ppm @ 120 min, 28c

So it would seem that the yeast has insufficient glycogen reserves, at least the type I was using. Which it should be noted the product I was using was at least 1 year out from manufacture date.

YOS test #4 (to evaluate scaling the process)
8 gal carbon filtered tap water @ 35c (in stainless brewpot with lid, no mash cap)
13 g dry yeast
13.4 g DME
Initial DO reading ~6.46 mg/l
0.47 ppm @ 20 min, 35c
0.26 ppm @ 43 min
0.25 ppm @ 60 min, 35c
0.19 ppm @ 90 min
0.18 ppm @ 130 min, 34.4c
0.25 ppm @ 170 min
0.18 ppm @ 15hr, 26c

The next tests were slated to evaluate heating this water to boil and then cooling to see what effect the temperature cycling had on the yeast in the water. Unfortunately I have not had time to do this yet, but will report in when that is finished. For the time being though I am very pleased with the results. What small amount of yeast used in this process should most certainly be denatured by the heat of the mash and turn into nutrient for the ferment. And while I have not actually read the Reinheitsgebot, it is assumed that since this method which only uses RHG compliant materials may very well be allowed.

[Owenbräu]

Outstanding Bilsch! Thanks for posting. Considering the total surface area for absorption, there is nothing better than yeast for consuming oxygen

[Brody]

Interesting test, very cool. Think you would you use something like this in conjunction with SMS? Thinking with the yeast being denatured by the mash you'd loose any protection during and after the mash.

[Bilsch]

Definitely. This might only replace the boiling and cooling to reduce DO levels. Yeast dies above 140f so you'd still need the SMB for protection in the mash.

[Owenbräu]

I wonder if active sauergut would be just as effective. You could eliminate DO and correct your pH in one step.

[mpietropaoli]

so yeast actively scavenges O2 even if there aren't fermentables present?

[Owenbräu]

[mpietropaoli]

Ah, sorry missed that.

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[Brody]

I'm wondering if preboiling and adding some active yeast would get it even lower? Or if the lack of 02 would make it too tough for the yeast to go to work.

[Owenbräu]

The whole point is to avoid the time and cost of pre-boiling, especially if you brew 50-100L batches. My propane bill has gone up quite a bit.