Low attenuation from harvested yeast.

I don't often repitch yeast but decided to repitch the Nottingham I'd used in my previous batch as it wasn't tainted with dry hops.
The original batch was a 1.059 beer pitched with 2 packets of dry Nottingham, mashed at 151, aerated by shaking and fermented at 63, finishing at 66. It finished out at 1.012 within 5 days and I considered it to be a healthy fermentation.

I didn't rinse the yeast but simply filled 3 sanitized jars equally (often recommended way to do it on here) with the slurry and put them in to the fridge.
So for my next batch, a 1.060 beer, brewed only 7 days after collecting the slurry, I pitched one of the jars of slurry directly into the 151 mashed wort, aerated by shaking and fermented at similar temps to the original batch.
It didn't take long to start up but was more sluggish than the original pitch and took 7 days to reach 1.018 which now appears to be the Fg as it has stood at that for 4 days.
Any ideas why it has stopped there? I know it's not too high but it should go lower with it being Nottingham.
I wonder which part of my practice is bad? My main guess is that the repitched yeast needs more oxygen than 2 packets of dry yeast or that I should have rinsed it to get the best of it.

Another thought is that I maybe pitched it too cold? I chilled the wort to around 66f but by the time It was in the fermentation chamber, the STC-1000 was reading 57-59 as it was a cold day. It took a good few hours to get to up.

After a week the slurry would have compacted. How many milliliters of the compacted slurry did you pitch?

flars said:

After a week the slurry would have compacted. How many milliliters of the compacted slurry did you pitch?

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To be honest I didn't measure the exact volume but it was around a third of the total slurry harvested from a 5 gallon batch, which should have been more than enough according to Mr Malty.

I say harvest yeast from the other side of things by saving a bit from each starter you make. That way, your yeast is healthier and purer from not being exposed to hop compounds and stressed through a fermentation. Though plenty of people have had success with harvesting slurry or dumping a new batch on top of a yeast cake, I always have preferred to treat my yeast as well as possible to ensure they do a good job

Was the malt bill of beer2 significantly different than that of beer1? Is it possible that beer2 contained more crystal/caramel malts and was therefore less fermentable?

m00ps said:

I say harvest yeast from the other side of things by saving a bit from each starter you make. That way, your yeast is healthier and purer from not being exposed to hop compounds and stressed through a fermentation. Though plenty of people have had success with harvesting slurry or dumping a new batch on top of a yeast cake, I always have preferred to treat my yeast as well as possible to ensure they do a good job

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I recently started doing this as well and LOVE it. So much easier on transfer day as well.

as far as the issue at hand it could be a couple things. did you warm up the slurry before pitching it at all? could have pitched too cold from what i have read but i honestly have never done that and have no experience there but i think stratslinger is likely already on the solution. Your malt bills could for sure be the culprit.

beerkench said:

To be honest I didn't measure the exact volume but it was around a third of the total slurry harvested from a 5 gallon batch, which should have been more than enough according to Mr Malty.

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There are several things that could have gone wrong. I am assuming you are brewing 5 gallons and your SG readings are with a hydrometer.

Your mash temperature could have been over 151°F in all or a greater proportion of the mashed grains, resulting in more unfermentable sugars.
Insufficient aeration. Dry yeasts can sometimes ferment out a small beer with no aeration. Liquid yeasts need good aeration, especially as the estimated OG increases.
May have been an under pitch because the available yeast was not evenly distributed in the three jars. One-third of the cake, based on my smallest harvest of 275 ml of clean yeast and estimating 2 billion cells per ml, should have been very close an adequate pitch.

Warm your beer to the upper 60°s, and give the yeast cake a gentle stir with a sanitized spoon. Let it go another week before checking SG again.

Hope this was somewhat helpful.

stratslinger said:

Was the malt bill of beer2 significantly different than that of beer1? Is it possible that beer2 contained more crystal/caramel malts and was therefore less fermentable?

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It was actually. The first recipe had no speciality malts in it whilst the latter contained 3% crystal and 3% amber. Could this be it?


Sent from hell
using Home Brew

Probably not - that's still a really low amount of specialty malts.

One thing that I read recently in White/Zainisheff's book Yeast, is that if you don't use an appropriately sized yeast pitch, or sufficiently oxygenate your wort, that it can lead to lower attenuation in subsequent repitches. If anything, it sounds like you overpitched on the first batch (2 packets of dry yeast into a 1.060 wort, unless the packets were really old, is probably twice as much as you need). I'm not sure if an overpitch could result in those kind of issues, but it'd be worth investigating.

Depending on if it is a yeast health or sugar composition issue there are two different paths to take. Which of the two it is can be determined by chromatography. (I'm working on a way to make this practical for us homebrewers)

Giving the carboy a swirl (instead of sticking anything into your beer) to resuspend the yeast, and moving it to a warmer area will generally help things along. If it is a yeast health issue then adding plant sterols, and or yeast nutrient should help. If it is a sugar composition issue, there isn't much you can do unless you want an extremely dry beer.

The dry yeast packets were nearing the use by date so I pitched 2 just to be on the safe side. I don't think that pitching 2 would be overpitching by a huge amount.
It's certainly not my mash temps as I use a Braumeister that has automated temperature control function.
It's soundning like the lack of oxygen which leads me to ask, why is it ok to underaerate when pitching a fresh pack of dry yeast but not ok when using it as a harvested pitch?

beerkench said:

Why is it ok to underaerate when pitching a fresh pack of dry yeast but not ok when using it as a harvested pitch?

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This topic really deserves much more discussion, but I'll try to sum it up.

Dry yeast is grown areobicly and dehydrated at a point when they have adaquate sterol content and glycogen reserve. (liquid) Yeast will quickly loose it's glycogen during storage (in the refrigerator) and requires oxygen to synthesis sterols. While the liquid yeast will work even without these, the lack of these will cause it to be slower.

How big were the jars? Three pint jars are a lot less yeast than 3 quart mason jars. You might have simply under pitched.

As stated try swirling the carboy to get the yeast back into suspension AND get it to a warmer temp if it isn't around 70 currently and see if that helps.

Man this is a head scratcher. Repitched yeast usually kicks ass. The pitch rate sounds like plenty, the time between batches is fine, the grain bill seems fine. I can only guess that the initial pitch and 1st beer weren't ideal, and maybe they didn't get quite enough O2. Then they went into another beer, and possibly didn't get enough O2 again. I don't think mash temp is the culprit, but I guess it's worth checking and calibrating all your instruments (hydrometer too).

To elaborate on glycogen and sterols:

Glycogen allows synthesis of sterols without pulling in sugar from the wort, and sterols aid in membrane permeability which helps in regulation of compounds in and out of the cell and is required for cell budding and growth. If the sterol level drops to about 10% of the original the cells ability to divide will be compromised.

Just the way the math works out this typically rears it's ugly head on the second batch.

With adequate aeration I agree, "repitched yeast usually kicks ass." However what is adequate is strain dependent. There are some good papers on this topic.

WoodlandBrew said:

This topic really deserves much more discussion, but I'll try to sum it up.

Dry yeast is grown areobicly and dehydrated at a point when they have adaquate sterol content and glycogen reserve. (liquid) Yeast will quickly loose it's glycogen during storage (in the refrigerator) and requires oxygen to synthesis sterols. While the liquid yeast will work even without these, the lack of these will cause it to be slower.

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Interesting information here.
The yeast had however only been in the fridge for a week after racking off from the original beer. Is this enough time for it to use up its glycogen?
I would really like to nail this yeast problem without having to buy an oxygen bottle. Otherwise it's just as cost effective for me to buy the dry yeast with every batch.

Maybe when you collected it, you managed to get some of the more flocculent yeast and they flocculated out before finishing the ferment.

beerkench said:

Interesting information here.
The yeast had however only been in the fridge for a week after racking off from the original beer. Is this enough time for it to use up its glycogen?
I would really like to nail this yeast problem without having to buy an oxygen bottle. Otherwise it's just as cost effective for me to buy the dry yeast with every batch.

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Yeah, a few days is all it takes. I could dig up a paper if you want. The way many breweries get around this is by aerating twice. Yeast will metabolize the oxygen in a few hours. There is a paper and a presentation I could dig up on this if you are interested.

WoodlandBrew said:

Yeah, a few days is all it takes. I could dig up a paper if you want. The way many breweries get around this is by aerating twice. Yeast will metabolize the oxygen in a few hours. There is a paper and a presentation I could dig up on this if you are interested.

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I would really be interested in reading the paper if it's not too much hassle for you to dig out. Thanks.

WoodlandBrew said:

This topic really deserves much more discussion, but I'll try to sum it up.

Dry yeast is grown areobicly and dehydrated at a point when they have adaquate sterol content and glycogen reserve. (liquid) Yeast will quickly loose it's glycogen during storage (in the refrigerator) and requires oxygen to synthesis sterols. While the liquid yeast will work even without these, the lack of these will cause it to be slower.

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If the conclusion is that harvested yeast need more oxygen than dry yeast, do you have a method or solution to using harvested yeast effectively without the need of using pure oxygen. Would a longer shake or a aquarium pump be useful in achieving this, and or do you recommend doing a starter with the yeast first?

beerkench said:

If the conclusion is that harvested yeast need more oxygen than dry yeast, do you have a method or solution to using harvested yeast effectively without the need of using pure oxygen. Would a longer shake or a aquarium pump be useful in achieving this, and or do you recommend doing a starter with the yeast first?

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Most of the time aeration is not a problem even with yeast that has been stored for longer than a week. It's the same with a vial of yeast you might buy. Oxygen requirements are strain dependent. If you do have a problem, or just want to play it safe, you can just aerate twice. Pour the wort back and forth between buckets just after you pitch. Clean the kitchen, then pour the inoculated wort back and forth again.

references:
BOULTON, Fermentation Management A Practical Guide (from mbaa.com)

and...

Jakobsen, M., and R. S. W. Thorne. "Oxygen requirements of brewing strains of Saccharomyces uvarum (carlsbergensis)—bottom fermentation yeast." Journal of the Institute of Brewing 86.6 (1980): 284-287.

WoodlandBrew said:

references:
BOULTON, Fermentation Management A Practical Guide (from mbaa.com)

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This was an certainly interesting read. I see that the experiments were based on huge commercial batches but I usually just pour in my yeast and let it ride. I never really mix it in with the wort properly. I guess I'll change my approach.
Do you think occasional swirling of our homebrew fermenters during fermentation could be of benefit to fermentation? If so I wonder why the practice is never preached.

beerkench said:

This was an certainly interesting read. I see that the experiments were based on huge commercial batches but I usually just pour in my yeast and let it ride. I never really mix it in with the wort properly. I guess I'll change my approach.
Do you think occasional swirling of our homebrew fermenters during fermentation could be of benefit to fermentation? If so I wonder why the practice is never preached.

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Agitation of the fermenting beer will speed fermentation. In my experience this is the main reason that stirred starters grow yeast more quickly than still starters. It's more common to swirl or shake the fermentor thought fermentation when making mead.

Im not sure why it isn't more common when brewing beer. Perhaps it's an unwarranted fear of oxidizing the beer. It could change the quality of the beer, but I wouldn't know how. Perhaps it's a "if it's not broke, don't fix it" mentality.