I've read a ton of debate between pitching a starter at high krausen or letting it finish out then cold crashing the night before or whenever and decanting. I'm wondering - because I am using the Brulosophy method of yeast harvesting which I'll do and crash tonight and pitch it tomorrow - my starter is currently at high krausen. If it's at high krausen say right before I go to sleep tonight, is it ok to cold crash the starter while it's at high krausen, or is there something going on there where if you're not pitching it into more sugar at high krausen you want it to fully ferment out and start storing up prior to cold crashing?
Cold crash starter at high krausen?
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D-Train
Well-Known Member
I've been using the same yeast harvesting technique. I typically ferment for 48 hours, split, and then cold crash for 48 hours. No doubt there's more lag time with this approach but as a homebrewer that isn't much concern. It's been working for me and I can't remember the last batch where I bought a pack of yeast.
Let the starter finish. If it's showing signs of fermentation it's not finished. More yeast cells are being produced. That is the purpose of a starter.
Cooling the starter will stop yeast activity and fermentation. This is not desirable.
Cooling the starter will stop yeast activity and fermentation. This is not desirable.
From my understanding, this isn't true. Yeast first goes through a growth phase, where it uses energy reserves to reproduce, this requires oxygen. After oxygen runs out, it moves into ethanol production. Granted, I'm sure ethanol is produced during the growth phase as well.
With that said, from what I've read, if you have fresh wort ready at high krausen, that's ideal. Your yeast starter had gone through its growth phase, and the cells are at the highest possible vitality. If you won't be ready to pitch your starter into fresh wort at high krausen, it's good to let them finish thier job before cold crashing. As they wrap up fermentation, they prepare for dormancy, thus being more prepared for a shocking cold crash.
We have differing understanding if the process.
There are many who advocate a small starter to be pitched at high krausen.
I don't but there is certainly a good rationale for it.
There is no sense in cooling a starter at high krausen. If you can explain that I'm all ears. Again, not talking about pitching at high krausen. That's a different ball of wax.
Oxygen should be readily available in a starter. The more agitation the better. That's not at issue.
The braukaiser has great info on all if this.
There are many who advocate a small starter to be pitched at high krausen.
I don't but there is certainly a good rationale for it.
There is no sense in cooling a starter at high krausen. If you can explain that I'm all ears. Again, not talking about pitching at high krausen. That's a different ball of wax.
Oxygen should be readily available in a starter. The more agitation the better. That's not at issue.
The braukaiser has great info on all if this.
At "high krausen" the yeast could still be reproducing. Sometimes my yeast show a krausen that starts a couple hours after making the starter and lasts through the period that the starter is running. So if you pitched when it looks high it might be just getting going.
On a stirplate your growth phase should be done in 18-24 hours. After that, leaving it longer is unnecessary as the yeast have already reproduced to cell counts to ferment the starter. So after 24 hours you are not increasing cell counts. If you cold crash the yeast will go dormant. When you decant and set the small amount left sit for a while the temperature will rise fairly rapidly. So when you pitch the yeast should not be significantly shocked. You can add a small amount of wort to get them energized. I have never done this step and my yeast starters usually take off within a couple hours after being pitched.
After the 24 hours: cold crash, decant then pitch the yeast slurry.
If you are not using a stirplate the timing needs to be extended because the yeast are not constantly exposed to oxygen thus the reproductive phase takes longer.
On a stirplate your growth phase should be done in 18-24 hours. After that, leaving it longer is unnecessary as the yeast have already reproduced to cell counts to ferment the starter. So after 24 hours you are not increasing cell counts. If you cold crash the yeast will go dormant. When you decant and set the small amount left sit for a while the temperature will rise fairly rapidly. So when you pitch the yeast should not be significantly shocked. You can add a small amount of wort to get them energized. I have never done this step and my yeast starters usually take off within a couple hours after being pitched.
After the 24 hours: cold crash, decant then pitch the yeast slurry.
If you are not using a stirplate the timing needs to be extended because the yeast are not constantly exposed to oxygen thus the reproductive phase takes longer.
muddy1015
Well-Known Member
Thanks for input - just pitched it I decided to try cold crash while it still had a good krausen on it last night and then pulled it out when I started the brew this morning
Well...wouldn't you know by the time I got around to decanting it had picked back up again pretty quickly and I was seeing some bubbles, etc. so I decided to just not decant and put the whole starter in (it was about 1L so shouldn't have too much effect on beer I think/hope)
I'd imagine in the end all these methods probably get you to the same place, but we'll see what happens here!
Well...wouldn't you know by the time I got around to decanting it had picked back up again pretty quickly and I was seeing some bubbles, etc. so I decided to just not decant and put the whole starter in (it was about 1L so shouldn't have too much effect on beer I think/hope)
I'd imagine in the end all these methods probably get you to the same place, but we'll see what happens here!
The reason you might want to cold crash at high krausen is because that is when the culture is at maximum cell density in the wort, as well as maximum yeast health. After high krausen, it's true that there is continued reproduction, but that reproduction is almost entirely for cell replacement, not growth. Unfortunately, that cell replacement uses up sterols and other nutrient reserves that the yeast need to multiply. So if you let your starter ferment to completion vs. crashing at high krausen, you'll end up with the same number of cells either way, but the yeast allowed to ferment to completion will have fewer nutrient reserves and be less healthy going in to your "real" fermentation.
How much this all matters in practice, I'm not sure. I typically let my starters go until the foam begins to subside and then crash and decant.
How much this all matters in practice, I'm not sure. I typically let my starters go until the foam begins to subside and then crash and decant.
I would disagree here as it implies yeast start dying off after this subjective point.
This is not supported by Braukaiser's data. Again it also implies that things will remain static once the starter is cooled.
The link essentially states that potting yet growth over time in a non- ideal growth medium like a starter is not feasible. The maximal cell count is dependent on the quantity of available nutrients. (Starter volume and SG within a reasonable window)
Picking an arbitrary time point at which to halt yeast metabolism (cold crashing) seems pointless to me unless all the usable nutrients are gone.
The linear model you describe simply does not apply. It assumes all the yeast are at the same metabolic stage. This is not the case.
There is a lot of discussions like these. I think the approach is needlessly complicated and not based in any sound rationale to be honest. All the stuff I've read on the topic does not support the practice of cooling a starter prior to its completion at some arbitrary visual point. (Look there is a lot of foam, better cool my starter because there will be no more budding of daughter cells.)
Pont me in the right direction to better science. I'm not claiming there is no other info out there to support what you describe. If you can share it with me I'd love to read it.
Braukaiser has tons and tons of fantastic info on starters. I'm certainly no guru but the excelence of his work is incredible. I would encourage anyone to read it and read it again.
Hermit
fuddle
Buy the 'Yeast Book' and read it. A lot of standard practice is not supported by the research done by professionals. I plan on rereading it soon.
Brukaisers data does not show that starters should "ferment out" and is totally unrelated to this question as it does not show yeast growth over time.
It shows that yeast will grow at different rates depending on their initial concentration in given volume of wort (how many billion yeast have to share the same gram of sugar). Read Kai's response to the first comment and he explains this.
It is true that not all yeast cells are in the same stage if life at the same time, but they do react as a population to some stimuli. Growth (generally across the population) does slow as sugar/nutrient/oxygen is depleted. Growth then reaches an equilibrium where yeast is budding at a rate determined by the amount of available sugar/nutrient/oxygen and others are simultaneously dying. That means that after a certain range of time the yeast population will stabilize for a given pitch rate to a given wort.
That time period is 12-18 hours as stated on the wyeast website and repeated by Jamil on Mr. Malty.
It doesn't matter what the starter looks like, high krausen or not. It's all about the growth curves and equilibrium yeast population which is based on a balance equation between wort volume, gravity, pitch rate, nutrient and oxygen levels.
This understanding of population equilibrium is not a debated topic. It happens. It is the foundation of the entire field of microbiology and is a fundamental concept which applies to every microbial lifeform, and all macroscopic life too: population reaches an equilibrium with food supply.
So yeast will grow according to the standard growth curve and the population will level off. Yes new cells are being produced continually, but old cells are also dying so the overall cell count changes very little.
In actual practice of making home brewed beer, I honestly don't think it matters much whether a starter sits for 0 hours, 18 hours, or 48 hours. Good beer has been made with all three and its just a matter of preference and semantics. Beer is forgiving.
I'm not sure you agree or disagree with me @Themadking .
I think agree?
Taking an arbitrary point in time with a non-ideal growth medium (a stirred starter) and inferring it has reached this maximal point gives an excellent chance there is more yeast to be had. Krausen formation is highly subjective.
Braukaiser's data is all open source and he clearly states that his data does not plot growth over time.
Let's see a link to something supporting the practice of cold-crashing at high krausen.
I favor the simpler approach.
I think agree?
Taking an arbitrary point in time with a non-ideal growth medium (a stirred starter) and inferring it has reached this maximal point gives an excellent chance there is more yeast to be had. Krausen formation is highly subjective.
Braukaiser's data is all open source and he clearly states that his data does not plot growth over time.
Let's see a link to something supporting the practice of cold-crashing at high krausen.
I favor the simpler approach.
Sorry I should have been more clear on that. I agree with you mostly, but I thought you were saying that brukaisers data was showing that yeast populations continue to grow until all fermentation activity is complete, but I was just misreading your first post I think.
I guess I was just confused about why you cited Kai's data when it doesn't really apply in this situation.
