cause of stuck ferm?

I brewed the DFH 90 min clone about 4 weeks ago and I just racked to secondary. I checked the SG and tasted a bit, it tastes fine but overly sweet and the SG is ~1.045. I'd like to understand what I did wrong so I don't make that mistake again.

My extract efficiency was pretty bad, somewhere around 45%, so I ended up adding 1.6 lbs of pale DME to get the OG I was aiming for, 1.088. I added the recommended amount of Wyeast yeast nutrient during the boil. I had a long and complicated starter process but I ended up pitching about 1/3 cup of thick, healthy slurry. I aerated with a ceramic airstone for about 20 mins. There were visible signs of fermentation within a few hours, and a large explosion at about 14 hours, because I used an airlock naively assuming that fermcap would take care of things. I was out of town most of the time but I believe the air temps were around 72, possibly a few degrees lower for the second two weeks.

The only thing that I can think of that may have caused fermentation to stop is the decrease in temperature, but it seems really unlikely.

What was your mash temp?

That does sound fishy. To me it sounds like you did everything well and should of had a good fermentation. but 1.045 what gives?????? If it were me i would A. drink some sweet nectar B. pitch some more yeast on it and let it continue to ferment

Yeah I washed the yeast after I racked to the secondary and I'm going to make a starter and repitch if the SG hasn't moved in a few days.

Mash temp was 149 for an hour, I think the conversion probably wasn't complete and that was part of the reason for my poor efficiency. I'm going to have to buy some of those test strips, and a mill.

I think I read somewhere that the temperature going down could cause the yeast to prematurely flocculate, any idea how much of a temperature change it takes?

I had a barley wine get stuck. The consensus was that because I didn't oxygenate the wort the yeast ran out of O2 and couldn't finish. Your original gravity was pretty high, if you didn't oxygenate that might be the problem.

I aerated for 20 mins with a ceramic air stone, should that be enough?

I would think that would be enough. I'm guessing you use a fish tank pump? I have hear of people oxygenating for up to an hour with that system. I now us an oxygen bottle with a valve, a vinyl tube and a very fine stone. One minute does the trick. Remember you want to oxygenate, not aerate your wort.

Yeah I'm using an aquarium pump, it seems to put out a lot of air. It has two air connections but if I use both the wort will bubble up out of the fermenter, even with fermcap. Oxygenating and aerating are basically the same thing. Air is mostly oxygen and nitrogen, and dissolving nitrogen in the water doesn't do anything bad since it's so stable.

Air is 30% oxygen and 70% nitrogen. Hopefully your filter, filters out small particles that might harbor bacteria. Like I said I use an O2 tank for one minute. I would give the beer a shot of O2 and re pitch new yeast (make a starter) making sure that you keep the beer under 70 deg. What do you have to lose?

The stuff I read about repitching said not to aerate the beer, just pitch a well aerated starter after decanting off as much of the wort as possible.

I have a batch that was stuck at 1.042 (started at 1.095). Last week I dropped in some yeast energizer and it dropped to 1.040 after two days and then stopped again. Yesterday I made a 1L starter with some yeast I washed from the primary and dumped the whole thing in this morning (at high kreuzen, about 18 hours in). The airlock has been bubbling away with increasing intensity since then (about 8 hours now) so it's looking a lot better. I'll take a gravity reading tomorrow and in a week to track the progress.

P.S.

This batch had 3 pounds of sugar in the boil so I think the yeast just quit after eating all the sugar.

NotALamer said:

The stuff I read about repitching said not to aerate the beer, just pitch a well aerated starter after decanting off as much of the wort as possible.

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OK, then if that's what you are comfortable doing, you should do that. With my barley wine I aerated and re pitched and it got going again. It hasn't completely stop fermenting yet. I have tasted it and I don't taste any off flavors, just a little sweet still.

So I guess I'll try to aerate longer next time, I can't really think of anything else other than temperature control. The air stone tends to make a lot of foam even with fermcap so I'll have to turn it off for a little while and let the foam subside.

What temperature did you ferment at??

EvilGnome6 said:

I have a batch that was stuck at 1.042 (started at 1.095). Last week I dropped in some yeast energizer and it dropped to 1.040 after two days and then stopped again. Yesterday I made a 1L starter with some yeast I washed from the primary and dumped the whole thing in this morning (at high kreuzen, about 18 hours in). The airlock has been bubbling away with increasing intensity since then (about 8 hours now) so it's looking a lot better. I'll take a gravity reading tomorrow and in a week to track the progress.

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1 day after repitching I'm down from 1.040 to 1.034. That's more like it! :rockin:

Awesome, I'm gonna check the SG in a few days and repitch if it hasn't moved. The air temperature has been around 72.

NotALamer said:

The stuff I read about repitching said not to aerate the beer, just pitch a well aerated starter after decanting off as much of the wort as possible.

Click to expand...

You read right. At this point even if you do manage to get some renewed fermentation going the yeast will not be utilizing oxygen to do it. Aeration at this point will become oxidation. So yeah, repitch like you said. And hope.

It really sounds like a mash problem. Poor conversion, incorrect thermometer, I couldn't know, but with your efficiency and now poor attenuation something sure seems off there.

If that is the case then playing with yeast will not help much because the sugars that are left would be unfermentable.

If all else fails you might try some amylase enzyme to break some of those unfermentables down to a more yeast friendly state. (Last resort though.)

Hmm we'll see what happens when I repitch I guess. I think my low efficiency was because I didn't mash long enough at such a low temperature, and the grind was fairly coarse. The mash started at 149 and finished around 147 an hour later, so it should be fairly attenuable.

I made a 1L starter last night with a jar of washed yeast and pitched it today. I checked the SG before I pitched and it was around 1.038 so it looks like transferring to secondary might have gotten it going again, but not very quickly. After listening to the BrewStrong on attenuation, I'm thinking it might have quit early due to temperature fluctuations. I don't think it fluctuated too much but they said even a few degrees could do it, and I wasn't around for most of the fermentation. Looks like a temperature controlled chamber will be my next project when I've got some money to spend on it.