Can someone shed light please, on why harvested yeast packaged in spout pouches in the absence of oxygen and wort/food, over time swells the pouches? How can co2 be produced when there are no nutrients and no oxygen in the bags? The ones we buy from the Wyeast, WhiteLabs etc. don't do that ...
Harvested yeast and CO2
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If you don't wash the yeast with saline there is still residual extract in the beer you collect with the yeast. Plus there is CO2 in the beer and the yeast itself that will slowly outgas. Yeast you buy is washed so there is little to no food/CO2 in the pouch.
Correct about the saline ! I completely discard the wort (of at least 98%) then I use 0.9% saline to store it (1 part saline - 2 parts yeast). I also flush with CO2 the pouches prior to filling them. I could use Nitrogen but I don't think it will do much of a difference (or will it?) . The only thing that comes to mind is that my pouches are not CO2 permeable (while the ones the big guys use are?). Do you mean yeast rinsing ? Or indeed yeast washing?
They don't? I try to avoid Wyeast because the pouches seem to puff up half the time (without the inner pouch being ruptured). I have an expanded pouch of Omega (Tropical IPA) in my fridge. The issue for me is more the storage room that an expanded pouch takes up than an issue with quality.
It makes me a little curious what White Labs does before packaging. I know they ferment the yeast in a plastic bladder, then seal up different sized pouches for brewery or homebrew pitches. I recall reading their patent on the process, and it seemed interesting.
Hmmmm...only a couple of times it has happened to receive a swollen pouch (with Wyeast) . With Omega , WhiteLabs and Imperial I have never received one...(so far I have received about 60-70 total) . That's why I was so curious how they do it 
acetobacter?
" In the general process of aerobic respiration, initially pyruvate is completely oxidized to carbon dioxide (CO2) in the citric acid cycle. "
just guessing...here what i was reading trying to figure it out myself....
https://onlinelibrary.wiley.com/doi/full/10.1111/1541-4337.12440
" In the general process of aerobic respiration, initially pyruvate is completely oxidized to carbon dioxide (CO2) in the citric acid cycle. "
just guessing...here what i was reading trying to figure it out myself....
https://onlinelibrary.wiley.com/doi/full/10.1111/1541-4337.12440
Reading into this article, regarding pyruvate: (I read from other sources) : When the yeast cell grows under anaerobic conditions, the pyruvate is converted into carbon dioxide and acetaldehyde. From there, during normal brewery fermentations, acetaldehyde will be converted to ethanol.
So that means that there is no pyruvate at the end of fermentation, correct?
Also further down it says: "... When ethanol has been completely oxidized and depleted, some genera of AAB, namely Acetobacter, Gluconacetobacter, and Komagataeibacter, can assimilate acetic acid and oxidize it completely to CO2 and water using the citric acid cycle and glyoxylate shunt, which is known as acetate “overoxidation” ... "
But in my case there is no oxygen in the packaged yeast, so how can "overoxidation" take place?
In general I was under the imression that no AAB exists in the yeast as these are considered spoilers...
There must be a hidden truth somewhere why this happens
So that means that there is no pyruvate at the end of fermentation, correct?
Also further down it says: "... When ethanol has been completely oxidized and depleted, some genera of AAB, namely Acetobacter, Gluconacetobacter, and Komagataeibacter, can assimilate acetic acid and oxidize it completely to CO2 and water using the citric acid cycle and glyoxylate shunt, which is known as acetate “overoxidation” ... "
But in my case there is no oxygen in the packaged yeast, so how can "overoxidation" take place?
In general I was under the imression that no AAB exists in the yeast as these are considered spoilers...
There must be a hidden truth
somewhere why this happens You're forgetting that yeast has glycogen reserves it can use at any time if it "wakes up". That glycogen is broken down into glucose units and those glucose units are, as you might have guessed, fermented into alcohol and CO2 if under anaerobic conditions.
You're forgetting that yeast has glycogen reserves it can use at any time if it "wakes up". That glycogen is broken down into glucose units and those glucose units are, as you might have guessed, fermented into alcohol and CO2 if under anaerobic conditions.
Indeed, but how can it wake up when stored in the fridge at 2C?
Besides that, is it safe to assume that the glycogen present is enough to cause the pouches to swell? How do the big guys avoid that? One thing (please correct me if I 'm wrong) is if yeast is stored under CO2 (therefore pressure) is bad for the cells causing mutations etc. Could longer starters (e.g. 4-5 days - instead of 2-3 - help? Without causing stress to cells staying due-to-longer-times under beer?)
CascadesBrewer mentioned above, that pouches puff up half the time , is just it almost never happened to me and from other people I asked around they mentioned the same.
Either way, If there are "things" going on during storage, I would assume this is not good for viability etc. as the cells are doing stuff when they shouldn't...please share your thoughts...
Besides that, is it safe to assume that the glycogen present is enough to cause the pouches to swell? How do the big guys avoid that? One thing (please correct me if I 'm wrong) is if yeast is stored under CO2 (therefore pressure) is bad for the cells causing mutations etc. Could longer starters (e.g. 4-5 days - instead of 2-3 - help? Without causing stress to cells staying due-to-longer-times under beer?)
CascadesBrewer mentioned above, that pouches puff up half the time , is just it almost never happened to me and from other people I asked around they mentioned the same.
Either way, If there are "things" going on during storage, I would assume this is not good for viability etc. as the cells are doing stuff when they shouldn't...please share your thoughts...
Well, much less than "half" but it has happened enough times that it caused me to avoid Wyeast packs. It might be something on my end like not keeping the packs cool on the way home from the shop, or fluctuating temps with packs stored in the door of my beer fridge. I just looked at the Omega pack and it is only partially puffed up. It was not like that when I put it in the fridge, but it has been in there for about a year (I picked up some extra supplies a year ago not knowing if stores were going to shut down).
My harvested jars of yeast tend to off gas quite a bit. Even after being in my fridge for a month or two, I have to keep the lids a little loose.
Carry on...I have learned a few things from this thread.
Yes that's exactly what's happening
and am looking for ways to avoid that...Happy to hear that
Well, I can't think of anything else how they do it, other than what mentioned... I even thought they probably use some permeable to CO2 pouches to relief excess Co2 inside (or some kind of sandwiched material between the layers with Co2 absorbing qualities? ) . The problem with Co2 (compared to Oxygen) is that its molecular diameter is bigger than Oxygen's...so if the pouch allows something "bigger" to exit wouldn't that mean that oxygen being "smaller" can enter? Ohhh so frustrating
I have read that WhiteLabs use (as they say) some special film, but I don't think that's the "deal maker" here, as others don't...My bet is that somehow they have these cells completely dormant when ours are not?
Maybe
If one from the "companies" is reading this post can help ? I would assume that glycogen reserves are not the cause here as A) low temperatures are used to store and B) 1-2 months time C) Also if the cells do that then so soon would go "bad" if you know what I mean, I could be wrong, please correct me if I am.
Hmmm...now that I 'm thinking around it: unless they use some agent to keep them dormant? Don't know if that would qualify as GM, many say they don't use GM, but then with various national and international laws a substance may not be required to appear on the bag... Just thoughts...
Edit: One more thing : if Glycogen reserves are the case, when we use petri dishes to store cells for months and months, when revived and propagated in test tubes and then larger and larger quantities (if the first sample was bad -e.g. mutated/starved etc.) wouldn't that mean that the final batch of cells would be bad? In my case (and am sure with others) this is not what's happening ...the results are fine.
i just did some math, and it would only take 0.02 grams of co2 to swell and entire 12 oz can....
figureing 5 gallons of co2 weighs 1.23oz's....and 5 gallons is 640 oz's, so i multiplied that by 28.3, got 18112...divided 1.23 by 18112....and well if it helps the conversation i got roughly 0.02 grams would swell up 12 oz jar, empty.....
edit: and figuring there's ~1 vol of co2 disolved in beer just from fermentation.....
figureing 5 gallons of co2 weighs 1.23oz's....and 5 gallons is 640 oz's, so i multiplied that by 28.3, got 18112...divided 1.23 by 18112....and well if it helps the conversation i got roughly 0.02 grams would swell up 12 oz jar, empty.....
edit: and figuring there's ~1 vol of co2 disolved in beer just from fermentation.....
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You are 100% correct and that is the reason why yeast packs have a BEST BEFORE date. They also keep loosing viability long before that date is reached.
You have to actually freeze them for that to happen but it makes handling a bit more complicated. The next best thing is to keep the yeast packs refrigerated at all times which is what we normally do.
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