Oxidation during fermentation

[KarlKrook]

https://imgur.com/a/hZv0AZG

I happened upon something I’ve never seen before. I’m fermenting a NEIPA
92% Extra Pale Maris Otter and 8% flaked oats. Mashed at 64C.

Hopstand at flameout for 10min.
Wort cooled while transferred to fermenter keg, the temp was ranging from 20-50C during the transfer and likely landed around 30C which was the goal. Pitched a good amount of OYL-091 and threw in my dry hops at the same time and then aerated a little with a wine degasser.

Day 4, fermentation is coming along just a little slower then expected, OG 1.056 SG 1.030 (final gravity according to forced fermentation with same wort and yeast landed on 1.010 after 4 days)

The beer was put under 15 PSI from beginning of fermentation and the pressure has been held the whole time so absolutely 0 oxygen has entered the fermenter.

The funny thing is, I’ve made loads of NEIPAS with very similar grain bills and hopping and this one is noticeably darker and slightly clearer. It looks and tastes typically oxidized.
And I know my oxidized beers, I used to bottle condition NEIPA and IPAs back before I knew any better. ;-)

So, how is this possible? Too warm yeast pitch? My previous batch was pitched at 40C with Sigmund Gjerne’s and had Golden Promise and that beer was fine at day 4 and much brighter.

To the photo. The beer on the left is the one still fermenting (day 4) in a closed environment with 100% no oxygen exposure whatsoever and has a lighter SRM / EBC than the one on the right which is 3 weeks old.

The fine one had more oxygen introduced hot side than the bad one too..

 

[ncbrewer]

Maybe it happened during transfer to keg? Just a wild guess.

 

[okiedog]

ncbrewer may be right, but sometimes it's hard to be certain unless you are checking it with a DO meter at all the different stages. I had a pumpkin ale that looked like the one on the left. It never cleared up, but I think it was because my mash pH was off. I nearly always keg condition so the yeast can clean up as much O2 as possible.

 

[Rodent]

So, how is this possible? Too warm yeast pitch? My previous batch was pitched at 40C with Sigmund Gjerne’s and had Golden Promise and that beer was fine at day 4 and much brighter.

you pitched yeast at 40C?

all of the yeasts I use for IPAs (west coast & NE styles) are recommended for 18C - 23C.

 

[ccous]

It doesn’t look oxidized. Could it just be that MO has a slightly higher lovibond than GP?

you pitched yeast at 40C?

all of the yeasts I use for IPAs (west coast & NE styles) are recommended for 18C - 23C.

he used kviek I think. High temps are ok, even beneficial for orange esters

 

[mongoose33]

In what way was your process different this time from the other times you brewed this? Same yeast? Obviously pitch temps differ.

You said you put it under pressure from the beginning. I'm assuming you added CO2; unless you're paying a lot extra for "pure" CO2, the typical beverage CO2 is going to be about 99.5% pure. If the remaining .5 percent is air, then of that 21 percent is O2, and thus you're pressurizing with gas that is .1% oxygen.

I typically wait until just a few points of gravity remain before full attenuation, close up the fermenter, and let itself-carbonate (ala bottle conditioning) the rest of the way. That way the CO2 is pure, as in produced by the yeast.

 

[azmark]

Oxidation at higher temps will be increased quite a bit. Heat speeds things up including the reactions that cause oxidation.

 

[couchsending]

Yeast starts to die at PSI above 10.

Lager yeast can handle more pressure, Ale yeast not so much.

I’m a big proponent of keeping O2 at bay but pressure fermenting is overkill unless you’re using a yeast designed for it.

 

[Vale71]

You said you put it under pressure from the beginning. I'm assuming you added CO2; unless you're paying a lot extra for "pure" CO2, the typical beverage CO2 is going to be about 99.5% pure. If the remaining .5 percent is air, then of that 21 percent is O2, and thus you're pressurizing with gas that is .1% oxygen.

I typically wait until just a few points of gravity remain before full attenuation, close up the fermenter, and let itself-carbonate (ala bottle conditioning) the rest of the way. That way the CO2 is pure, as in produced by the yeast.

Just out of curiosity, how do you purge the headspace in your fermenter after pitching?

 

[Vale71]

Yeast starts to die at PSI above 10.

No it doesn't. Actual death starts at around 30 bar or above, but of course lower pressures will still affect the yeast, just nothing so dramatic as killing them off.

 

[mongoose33]

Just out of curiosity, how do you purge the headspace in your fermenter after pitching?

?? I don't understand. I don't purge the headspace after pitching. Two things happen to the oxygen in that headspace. One is some of it is absorbed into the wort where it is used up by the yeast. The other is it's purged out of there by the CO2 produced by the yeast.

 

[Vale71]

So basically you are starting with 21% oxygen in the headspace whilst the OP is maybe, in the worst case, starting with 21.1% (assuming 99,5% CO2 purity which is below food grade standard and that the remaining 0,5% is indeed all air which is actually never the case). Why do you think the fermenter will only contain "pure" CO2 in the end in your case and will on the other hand be significantly contaminated with O2 in his?
Assuming of course identical conditions such has same OG and final attenuation and headspace to wort volume ratio.

 

[SRJHops]

My best guess is the slow fermentation start, though you said it was under pressure the whole time? My NEIPA's are going strong the next morning, so the headspace oxygen has been pushed out quickly. Maybe consider switching yeast? I use Safale-04, though there are other yeasts that also work more quickly.