National Homebrew Club Ireland

Did a sweet stout about two weeks ago. Fermented vigorously for 2-3 days then slowed as expected. OG 1.062, gravity at day five was only down to 1.030. Bit high, but all the lactose and crystal malt plus mash temp of 68 probably explains it. I increased the temperature from 18 degrees up to 20 and roused the fermenter to see if I could get a few more points out of the yeast but it was still at 1.030 two days later. Then the weirdness: at this stage there is no krausen and no airlock activity, but suddenly another day later the airlock is going like mad and there is a thick raft of yeast floating on top, thicker even than when fermentation was at it's most active. This yeast raft has persisted for the past week now and the airlock is bubbling like mad, but there has been absolutely no change in gravity. Beer smells and tastes fine, but I have never experienced anything like this before. Yeast was Mangrove Jacks Empire Ale (sent by mistake from homebrew shop instead of S04), which I've never used before. Has anyone ever experienced anything similar?

I don't see how you can have that kind of metabolism but no gravity change.

Double check your hydrometer, take readings at 20C and correct for  temp. Also taste your samples for sourness or declining sweetness

Quote from: TheSumOfAllBeers on November 15, 2016, 10:12:35 AM
I don't see how you can have that kind of metabolism but no gravity change.

Double check your hydrometer, take readings at 20C and correct for  temp. Also taste your samples for sourness or declining sweetness

Exactly! I'm baffled.

Hydrometer is accurate and beer tastes fine. Taste hasn't changed since last week. I have no idea what's going on!

I've had similar experience with Mangrove Jacks yeast. I did a beer and it took off like a rocket then stopped at 1.030. Did exactly the same as you by ramping up the temp from 18 to 20 for a few days and nothing.

I didn't rouse the yeast at all, I considered it a stalled fermentation and moved on.

I've had varying experiences with Mangrove Jacks, most recently it took almost 3 days to see any activity then it chugged along for another 5 days producing this amazing clean and well attenuated beer.

Remember a lot of the Mangrove Jack yeast packs, while being 11g, have a lower cell density then the other brands. In most cases, you're looking at 50-60B cells per pack, in comparison to ~100B in a liquid vial and ~120B in something like US-05 (I think!)

This can account for the lag some people get, as you're effectively under-pitching.

+1, 2 packs for big beers, great product but a lightweight.

I would never have picked the particular yeast myself, as I said it was sent to me by mistake. I said I'd chance it though. Will be sticking to US05 and S04 in future. Anyway, I have this beer cold crashing now for bottling in a few days. We'll see how it turns out.

This is very strange. I just done an exceedingly good IPA recipe from HBC and they sent me mangroves also. Never used it before. It took off fine, after 3 days it looked completely different, and it went from 1.060 to 1.022. Hasn't budged since either, after ramping up the temp to 21 (from 18) and also rousing the trub.

Debating wether to actually dump it......haven't tasted it yet.  But finished at 1.022 I'm already dreading it being clawingly sweet


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On reflection, it states on HBC website that this recipe should be 4.6%......which is bang on with 1.022. Just never had a beer finish this high on me, what to do


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Try it and see! It is high, but sounds like your yeast either stalled, was underpitch or wasn't kept at a steady temperature. See how it tastes, look at your notes and try it again with tweaks.

Watch out for specialty malts in the grist, they may contain a high proportion of sugars that certain yeast strains cannot metabolise

Interested reader of this thread, I done one of the HBC mash kits at the weekend as my first AG attempt. It was bubbling away like mad the first couple of days but I noticed a slow down last night aswel. I'll check the numbers when I get in from work.

If HBC are using Mangrove yeasts in all their mash kits they really should be sending people two packs for anything with projected OG of 1.060 or more. Someone write a sternly worded letter!!

I've had serious problems with Mangrove Jacks yeast, and I've tried a few. Their French Saison is a beast though!

Quote from: vinyljunkie on November 17, 2016, 11:39:23 AM
Interested reader of this thread, I done one of the HBC mash kits at the weekend as my first AG attempt. It was bubbling away like mad the first couple of days but I noticed a slow down last night aswel. I'll check the numbers when I get in from work.

10 days on this has fully fermented out and tastes lovely! FG is about 1.008