reuse of yeast cakes - consistent stuck fermentations - lets discuss

[lone_wolf]

Brudders and Sistaz
I am being suddenly yet consistently and oxymoronically plagued with stuck fermentations on batchs of beer I brew on yeast cakes. The operative word here is consistently - down to the FG that the damn batches stall on.
first the environmental factors:
1. I always pitch close to the entire yeast cake
2. I always pitch into wort that represents a decent gravity step-up. e.g cake from a 1045 batch into a 1062 or summin
3. I do not brew huge beers. OGs are never more than 1066ish
4. I typically pitch a cake that is less than three weeks old (from the start of the first batchs fermentation)
5. I always brews super fermentable wort (mash 150f religiously)
6. I control my temps - never above 70f
7. I use S-05 religiously (basically i have no imagination)

Secondly the experience:
1. After repitching, fermentation starts almost immediately(why wouldnt it, I must have a gajillion active cells available)
2. becuase I control temps, fermentation is vigorous but not explosive for about 3 days. Then it just stops. super abrubtly.
3. The wort is now give or take a point, always now at 1020. I can see the yeast cake reforming pretty quickly at this point too, like its pre-flocculating

WTF?

I have tried gently restirring the yeast into suspension, but this only knocked 4 points of one batch and didnt make a difference on another.

I am throughly confused by this. If it makes a difference Im a fairly experienced AG brewer and I dont recall having these issues in the past. Someone got a shoulder to lean/cry on?

 

[bu_gee]

Do you use a yeast nutrient when you repitch?

 

[brew_ny]

do you raise the temperature towards the end ?

I reuse US-05 all the time, after 72 hour at 65 f I let the temperature go up to 70 f

to finish

always hit my FG without a problem, I really like 05 for an ale yeast

all the best

S_M

 

[lone_wolf]

Do you use a yeast nutrient when you repitch?

hmmm thats an interesting point.
The answer is no I dont, only coz I figure what I have is a billion billion cells that have recently proved themselves in battle and are fighting fit.
Is this yeast-nutrient on a repitch conventional wisdom?

 

[flars]

For FG are you using a hydrometer or refractometer?

 

[bu_gee]

hmmm thats an interesting point.
The answer is no I dont, only coz I figure what I have is a billion billion cells that have recently proved themselves in battle and are fighting fit.
Is this yeast-nutrient on a repitch conventional wisdom?

The manufacturers of the yeast put an adequate amount of nutrient in their packages for one brew. The second one is on you. The yeast need more than just maltose to thrive. I am however surprised by the suddenness of the drop-off in activity.

It is my understanding that the mash needs special treatment if you're looking to repitch. Either you need to add a commercial nutrient or follow a special procedure during mashing to help extract those nutrients from your grains.

I should say tho, that I'm not a repitcher, so this is all based on reading and not experience.

 

[lone_wolf]

For FG are you using a hydrometer or refractometer?

Hydrometer - I should say it did occur to me for a sec that my hydro might be faulty but it appears 100% reliable on all the first generation batches?

 

[lone_wolf]

The manufacturers of the yeast put an adequate amount of nutrient in their packages for one brew. The second one is on you. The yeast need more than just maltose to thrive. I am however surprised by the suddenness of the drop-off in activity.

It is my understanding that the mash needs special treatment if you're looking to repitch. Either you need to add a commercial nutrient or follow a special procedure during mashing to help extract those nutrients from your grains.

I should say tho, that I'm not a repitcher, so this is all based on reading and not experience.

Thats the thing, I figure an issue with yeast nutrition would manifest itself differently - slow start or weaker than expected fermentation, off flavours etc. Not a perfect fermentation for 3-4 days and then silencio.

That said, you have given me a glimmer of hope and I'm going to cling to it. thanks for your comments bro!

 

[bu_gee]

I found a post on here where a guy boils a package of bakers yeast in a little bit of water to kill the yeast and keep the nutrient and puts that in his beer.

If nothing else, it seems a cheap way to test if that is your issue.

 

[bu_gee]

Thats the thing, I figure an issue with yeast nutrition would manifest itself differently - slow start or weaker than expected fermentation, off flavours etc. Not a perfect fermentation for 3-4 days and then silencio.

That said, you have given me a glimmer of hope and I'm going to cling to it. thanks for your comments bro!

Good luck. Let me know if it helps.

 

[stpug]

The main point I'd like to emphasize is that you are doing yourself and your beer a disservice by pitching on the entire yeast cake. My recommendation would be to, at the very least, toss 3/4 of the yeast cake down your drain and pitch on the remainder.

Wort has sufficient nutrients for yeast growth when starting from a reasonable cell count unless you're using high adjuncts or simple sugars, in which case you might some nutrients.

Oxygen is also very important in yeast growth.

Yeast growth is important in fermenting wort to a proper level with proper esters - regardless of strain.

 

[lone_wolf]

The main point I'd like to emphasize is that you are doing yourself and your beer a disservice by pitching on the entire yeast cake. My recommendation would be to, at the very least, toss 3/4 of the yeast cake down your drain and pitch on the remainder.

Wort has sufficient nutrients for yeast growth when starting from a reasonable cell count unless you're using high adjuncts or simple sugars, in which case you might some nutrients.

Oxygen is also very important in yeast growth.

Yeast growth is important in fermenting wort to a proper level with proper esters - regardless of strain.

I did think about this as a possibility, but I cant get a grip on the principle of the bad-science involved. Ive read all the articles on overpitching leading to missing esters (if thats important) and over attentuation etc but never stuck fermentations?.
I also pride myself on my wort oxgenation habits. I siphon and splash from kettle to fermentor and then just to really show off, I typically perform about 5 mins of fermentor shaking. and yes my arms and lower back are completed screwed for a week afterwards

 

[bu_gee]

I've been trying to wrap my head around this for the past few hours (mostly because it is an interesting problem) and I have come up with the following conjectures with the tests for potential solutions:

1. Overpitching may be an issue here only because once they hit the fresh sugar, they just go into overdrive and use up their dwindling resources that much more quickly and this might explain the sudden stop versus a gradual one. Solution: Try pitching 1/4 of the cake and see what happens.

2. Oxygenation is less likely to be a concern/issue here just because your yeast are already alive and kicking. I don't think you have to reduce your oxygenation, but you may not need to be as extreme about it as you do for the first pitching. Solution: Not really a solution, but once you have the problem figured out, maybe go back and try a batch without as much vigorous shaking and see what difference it makes.

2a. The excess of oxygen may require the addition of citric acid since the yeast need to return to citric acid cycle, aerobic respiration.

3. The wort change might be causing an excess of need for nutrients. If you pitched on the exact same wort twice, you might enjoy better success because the yeast have already tooled up for that mix of food. Solution: Try the exact same recipe twice on the same yeast.

4. By the time you repitch, the yeast may be in what I call "redigestion mode" (where they're breaking down by-products more than they're breaking down sugars) so they may be having a hard time going back to sugar digestion especially without the nutrients they need to make up the enzymes they need. Solution: Rack off of the primary early into a secondary and try pitching on that yeast cake.

These are all in addition to the yeast nutrient. Naturally, I'd recommend trying to change one thing at a time so you can tell what the problem really is.

 

[kaconga]

Sounds like you have a mutation. Are all these batches the same yeast cake? I think it could be a petite mutation, one in which the yeast fail to utilize the oxygen for growth and this stunts the colony. Also you might have accidentally selected for more flocculent yeast and they are dropping out before the job is done.

 

[bu_gee]

Sounds like you have a mutation. Are all these batches the same yeast cake? I think it could be a petite mutation, one in which the yeast fail to utilize the oxygen for growth and this stunts the colony. Also you might have accidentally selected for more flocculent yeast and they are dropping out before the job is done.

Selecting on a mutation requires a massive die-off which that mutation protects against. What he is describing doesn't seem to indicate that there was a massive die off or a stressor to select on a mutation. Also, what is the chance that multiple mutations that exhibit themselves in the exact same manner would happen from different batches of yeast.

Also, since he is using the whole yeast cake, I would think that he's not picking yeast mechanically which is the only way I can think of to pick more flocculent yeast.

 

[kaconga]

Selecting on a mutation requires a massive die-off which that mutation protects against. What he is describing doesn't seem to indicate that there was a massive die off or a stressor to select on a mutation. Also, what is the chance that multiple mutations that exhibit themselves in the exact same manner would happen from different batches of yeast.

Also, since he is using the whole yeast cake, I would think that he's not picking yeast mechanically which is the only way I can think of to pick more flocculent yeast.

I was a bit vague on if the OP was referencing a first and second generation each time or just kept reusing yeast. I reread it and agree with you that mutation is not a likely culprit. Although I would like to point out that petite mutants can and will occur with far greater regularity than people realize. However for the entire colony to become compromised it would be nigh impossible with what the OP is describing. Thanks for keeping me honest

 

[pdxal]

How are you storing the yeast cake between batch #1 and batch #2?

 

[lone_wolf]

I've been trying to wrap my head around this for the past few hours (mostly because it is an interesting problem) and I have come up with the following conjectures with the tests for potential solutions:

1. Overpitching may be an issue here only because once they hit the fresh sugar, they just go into overdrive and use up their dwindling resources that much more quickly and this might explain the sudden stop versus a gradual one. Solution: Try pitching 1/4 of the cake and see what happens.

2. Oxygenation is less likely to be a concern/issue here just because your yeast are already alive and kicking. I don't think you have to reduce your oxygenation, but you may not need to be as extreme about it as you do for the first pitching. Solution: Not really a solution, but once you have the problem figured out, maybe go back and try a batch without as much vigorous shaking and see what difference it makes.

2a. The excess of oxygen may require the addition of citric acid since the yeast need to return to citric acid cycle, aerobic respiration.

3. The wort change might be causing an excess of need for nutrients. If you pitched on the exact same wort twice, you might enjoy better success because the yeast have already tooled up for that mix of food. Solution: Try the exact same recipe twice on the same yeast.

4. By the time you repitch, the yeast may be in what I call "redigestion mode" (where they're breaking down by-products more than they're breaking down sugars) so they may be having a hard time going back to sugar digestion especially without the nutrients they need to make up the enzymes they need. Solution: Rack off of the primary early into a secondary and try pitching on that yeast cake.

These are all in addition to the yeast nutrient. Naturally, I'd recommend trying to change one thing at a time so you can tell what the problem really is.

I think your point #4 is the most interesting one. Ive also been brain-racking as to when these problems started and *I think* its when i started being fascist on my temp control in primary. What this has translated to is quite long slow primary fermentations on the first batch (like close to 3 weeks on s-05 which I find to be a slow fermentor at best of times).
In the past I wouldnt temp control which would translate into a hot and fast fermentation on the first batch and from memory I would reuse the yeast cake at about a week. As you say its plausible under the latter conditions the yeast are still amped and gagging for maltose, but in recent times and after 3 + weeks they are confused about what their next meal should be.

 

[bu_gee]

Although I would like to point out that petite mutants can and will occur with far greater regularity than people realize.

Possibly far more than we'd like to think. Estimates for saccharomyces base pair mutation are roughly between 3*10^-10 and 6*10^-10. That coupled with a genome size of 1.2*10^7 roughly translates to 1 of every 250-500 cells with a DNA copying error. My guess is that the majority of these errors are lethal.

One study I found showed roughly 1100 successful mutations (those that don't inhibit the survival of the yeast) in 311,000 generations.

 

[stpug]

Yeast, Chapter 5, page 121, second paragraph:

"What are the consequences of overpitching or underpitching? In general,
underpitching affects flavor more, while overpitching negatively affects yeast
health more over generations. However, both can result in less than ideal
fermentation with high level of diacetyl, acetaldehyde, and low attenuation."

So, if there is a remote possibility that severely overpitching is causing low attenuation, isn't it simple enough to simply trash 3/4 of the cake and pitch on the remainder, just to test the possibility?

 

[kingwood-kid]

I'm with St Pug. Here's a link to support the point: http://sciencebrewer.com/2012/03/02/pitching-rate-experiment-part-deux-results/

If you can't be bothered to read the entire thing, it contains a quote from Brooklyn Brewing's Garrett Oliver. "Overpitching ages the culture – fewer daughters, over time, leaves you with a lot of battle-weary scarred cells with inflexible membranes that are no longer at their best. And not as many young, scar-free new cells.”

 

[davejanssen]

Cool, I'm stpug brought up the yeast book. As people have previously pointed out, pitching the entire cake is not great and may be contributing to your problems.

I would suggest adding yeast nutrient and pitching a portion of the cake to see if that helps.

Also potentially at play is that shaking/splashing wort for aeration doesn't get you quite enough O2. Even if you get complete saturation with ambient air, it is a bit low (especially for higher OG beers). Check out the Yeast book, pp77-83. This can lead to under-attenuaton (see figure 4.2 on pp.80) and if you continue repitching yeast that have been O2 stressed it can cause further under-attenuation (fig 4.5 on p.83).

 

[bu_gee]

I hate to bump, but I'm curious to see if you have had any success with repitching. If so, what did you discover?