stuck fermentation - mash temp or under pitching?

[klinus]

Hi! I've made some small 5 liter (1.3 gal) batches, and all have been going pretty smooth so far. But I decided to upgrade a little to 10 liters recently. For the 5 liters I used half a packet of US-05, but when I was going to pitch my 10 l batch, i read on the label that a packet 11.5g is enough for 20-30 litres, so I decided to still pitch only half.

I brewed an ipa, OG 1.069, and the first couple of days it bubbled away good in the closet, and everything was nice. 12 days later, i checked SG to see if it was time to dry hop, but I was only down to 1.032, and has been stuck there for three days now.

Today, i took a chance and pitched another half packet of us05 in there, and now, around 7 hours later, the airlock is bubbling again.

Does that mean that I under pitched, and should use a whole 11.5g for my 10l batches in the future?

Or did I mash too high? I think I did. I use biab, but read somewhere (for an all grain - non biab recipe) that it was good to get your strike temp around 8-10 degrees C over your desired mash temp. So I threw in the malt at 74 C (165F), but it went down to my desired temp at 68C (154F) in around 5 minutes.
Now I've read a little more, and I realize that I might not need to exceed my temp that much, and also that maybe I should mash lower as well?

thanks!

 

[Nuggethead]

As far as the stuck fermentation goes, what was the temperature in the closet.
According to Mr. Malty calculator, you needed .4 of an 11.5 gram package, so under pitch should not be an issue.

 

[klinus]

As far as the stuck fermentation goes, what was the temperature in the closet.
According to Mr. Malty calculator, you needed .4 of an 11.5 gram package, so under pitch should not be an issue.

thanks for the reply! The temp in there is 22 C, 71.6F, and has worked perfectly with the other beers, another 5 liter is fermenting in there right now.
I have to check mr malty, because I tried brewersfriend a couple of hours ago, and it said that I was 9 billion cells short (see screen shot below). I might have made a mistake somewhere there though, I didn't really get all that with the cell density.

 

[Nuggethead]

Sorry, i double checked the info you gave and M.Malty says you needed 7 grams of dry yeast for a 1.068 Ale at 2.60 gal. or 10L.
So even at that, you weren't to bad at 1/2 package/5.75 grams.

 

[Hex23]

Was the yeast expired or mistreated in any way? Did you aerate or oxygenate? 1.069 is getting pretty high. If your thermometer is accurate 154 isn't so high that it would make your wort that unfermentable.

Sent from my DROID RAZR using Home Brew mobile app

 

[klinus]

Was the yeast expired or mistreated in any way? Did you aerate or oxygenate? 1.069 is getting pretty high. If your thermometer is accurate 154 isn't so high that it would make your wort that unfermentable.

Sent from my DROID RAZR using Home Brew mobile app

Uhm, I dont think so. I half the packet about a week earlier, but kept it wrapped in aluminium foil in the fridge until a couple of hours before brewing, so it should be ok, right?
Yeah, I shaked the bucket pretty wildly, for around a minute, but I dont know, maybe it wasnt enough? Is there anything I can do about that now? 1.069 is pretty high, got a little higher efficiency and a little more boil off than calculated.
The thermometer is one of those analog chemistry thermometer, its brand new and I think it should be correct. A little hard to read though, it flickers a lot sometimes. Going to se how accurate it is with boiling water though!

Next time, do you think I should pitch a whole packet, or try mash at a lower temp?

 

[TimmyWit]

Are you re-hydrating your yeast prior to pitching? It looks like you slightly under-pitched which isn't a big deal by itself. But, if you didn't re-hydrate your yeast prior to pitching, you lost some viability on top of slightly under-pitching.

Now that fermentation has started, if you do pitch more, re-hydrating would be even more critical. As the cells are re-hydrated, they gain the ability to regulate what passes through the cell wall. If they go directly into fermenting beer, all that alcohol will be allowed to pass.

Here's a good write-up on re-hydrating:
http://www.northernbrewer.com/connect/2010/06/the-importance-of-being-hydrated/

 

[calvey]

+1 for the idea of rehydrating the yeast. I know the calculator says <1 packet of dry yeast, but I have to say it's not a bad idea to go ahead and pitch the whole thing. I never really know how nicely those packets were treated before they got to me, so I assume less than optimum conditions for the yeast viability.

Also, for you strike temp, you can use my http://biabcalculator.com tool to get it right. It's specifically for BIAB style, whole volume strike/mash and has done pretty well in real life testing. Be sure to measure your grain temperature too - it's a little difference, but it counts.

 

[Hex23]

In theory dry yeast don't need much, if any, 02. But it shouldn't hurt. Dry yeast are suspended in a state where their reserves are built up. But your gravity is at a point where I think using pure O2 could always be helpful.

Sent from my DROID RAZR using Home Brew mobile app

 

[Weezy]

Could the fermentation temp have varied much? It doesn't seem like you under pitched enough for it not to attenuate more fully, especially with that yeast. Its obviously not your mashing since the ferment started up gin after repitching.

 

[JordanKnudson]

Also, for you strike temp, you can use my http://biabcalculator.com tool to get it right. It's specifically for BIAB style, whole volume strike/mash and has done pretty well in real life testing.

+1. The grain will drop the temperature of your strike water pretty immediately by several degrees, but I haven't ever encountered a situation where the strike temp needed to be 11 degrees F above target. You'd have to be doing a pretty thick mash for that to be necessary.

 

[klinus]

I think I found the problem, it was the mash temp. I brewed yesterday, and tried another thermometer, and it showed around 7-8 degrees C higher, and boiling wort was only 92 degrees C hot with the old one (should be 100C). That would mean that I actually mashed in at 74+7 = 81 C (177F), and then it dropped to 75C (167), and that, I guess, would be way to hot?

Although the fermentation started again when I added more yeast, it didn't last for long. I'm gonna look again tomorrow, hopefully it dropped a few points, but I doubt it dropped all the way down to target, 1.016. I guess this batch will be 10 liters of sweet ipa, but at least I learned something.

@Timmywhit & Calvey: nope, didnt rehydrate, I was under the impression that dryyeast was ready to, just sprinkle, but Im gonna read up on that! Thanks! Do you just rehydrate it in a bit of water a couple of minutes prior to pitching, or does it need longer?

 

[Hex23]

Yes, 177 dropping to 167 is def too hot. Its a little surprising to me that you were able to get such good efficiency. Those temps would do a pretty good job denaturing enzymes. I'm not sure what the gravity contribution of starches is, but definitely lower than sugars. Maybe you ended up with lots of long chain dextrins which would boost gravity.

Best to follow strain specific manufacturer instructions for rehydration.

Sent from my DROID RAZR using Home Brew mobile app

 

[Hex23]

I guess this batch will be 10 liters of sweet ipa, but at least I learned something. ?

It may not be sweet, just heavy mouth feel/body. Its a common misconception that high FG equals sweet. It can be the case, but if your yeast ate through the truely fermentable parts of an all malt wort, then it should not be very sweet.

 

[Weezy]

Mash temp doesn't explain the ferm stalling then restarting when you add more of the same yeast.

 

[Hex23]

Mash temp doesn't explain the ferm stalling then restarting when you add more of the same yeast.

I think OPs signs that ferm restarted was more bubbling. Bubbles are no guarantee of ferm. If OPs gravity changed, then yes, maybe the first pitch had stalled.