Yeast Pre-Oxygenation - Oxygenate your yeast, not your wort.

[Craiginthecorn]

Would a starter with an active stir bar produce any oxygen? Curious. No idea.

Never tried that unless my stir bar adds some oxygen. I usually rock a bucket.

Curious to hear experiments on this.

A starter never "produces" oxygen. The stir bar is more about keeping the cells in suspension than adding more oxygen, which is why a whirlpool cone isn't needed. What's interesting to me is the question of how to load up yeast cells with the sterols and fatty acids needed for reproduction in the starter. My guess is that this is why the low gravity/high FAN starter discussed on the BruLab works. Not enough food to progress beyond the lag phase into the growth phase.

 

[mashdar]

A starter never "produces" oxygen. The stir bar is more about keeping the cells in suspension than adding more oxygen, which is why a whirlpool cone isn't needed. What's interesting to me is the question of how to load up yeast cells with the sterols and fatty acids needed for reproduction in the starter. My guess is that this is why the low gravity/high FAN starter discussed on the BruLab works. Not enough food to progress beyond the lag phase into the growth phase.

FWIW, Braukaiser detected stir-speed dependent yeast growth. Do you have data or guidance from elsewhere indicating a vortex does not matter?
https://braukaiser.com/blog/blog/2013/03/25/stir-speed-and-yeast-growth/

edit: spelled Braukaiser wrong!

 

[ninkwood]

I just did for the first time on an American Pilsner (aka a Hoppy American Lager). 2L starter, crash, decant, dilute with 2 liters of wort, oxygenation with a stone for 30 seconds, let it rest while the remaining wort was chilling down to the final pitching temperature.

I did essentially the same thing as you're describing here on 2 of my last three batches. I made a starter, crashed, decanted, and then pumped the first ~2L of chilled wort onto the yeast and put back on the stir plate (I've yet to invest in o²) for a 2-3 hrs while I finish cleaning and in the case of a lager, let it finish cooling in the fermentation chamber.

Both beers have come out great, and I was most impressed with the lager. It finished very clean, especially considering it's a Czech strain.

 

[Craiginthecorn]

FWIW, Braunaiser detected stir-speed dependent yeast growth. Do you have data or guidance from elsewhere indicating a vortex does not matter?
https://braukaiser.com/blog/blog/2013/03/25/stir-speed-and-yeast-growth/

I always love a comment based on hard science! I stand corrected and just a little bit more knowledgeable than I was before.

 

[ninkwood]

I brewed a hazy IPA today and thought I'd shoot a video of my current method for aerating yeast with a small portion of the finished wort. With a 2" stir bar, I can get a pretty good vortex going. I know this isn't the same as hitting it with pure o2, but it's the best I've got at the moment.

 

[Broothru]

What about the common argument that yeast on a vortex producing spin will become "stressed"? I'm not sure how that argument can be proved or disproved, but it sure has it's adherents. Further, where is the balance point where the number of "stressed" cells compared to fewer "contented" cells becomes empirically tipped in favor of one method or the other? All I want is a metric crap ton of cells, munching away at all those sugars I'm able to coax out of the grist. Are fewer 'happy' cells better than more 'angry' ones?

 

[Bobby_M]

What about the common argument that yeast on a vortex producing spin will become "stressed"? I'm not sure how that argument can be proved or disproved, but it sure has it's adherents. Further, where is the balance point where the number of "stressed" cells compared to fewer "contented" cells becomes empirically tipped in favor of one method or the other? All I want is a metric crap ton of cells, munching away at all those sugars I'm able to coax out of the grist. Are fewer 'happy' cells better than more 'angry' ones?

I think that's an argument for limiting stir time because the stir bar is physically beating up the yeast cells. Stirring harder is bad and stirring longer is too. Whether a vortex would help draw oxygen in would be very dependent on how much air exchange you're getting. I don't think I've ever heard an explanation of why we use Erlenmeyer flasks vs a wider opening beakers. Loose fitting foil, even though a little leaky, would seem to encourage a lot of escaping CO2 velocity that would reduce room air from getting in. Hmm, extremely slow dosing of pure O2 through the foil?

 

[IslandLizard]

What about the common argument that yeast on a vortex producing spin will become "stressed"?

The vortex induces a "shear force" on the yeast cells, which can damage them over time.

From what I've read the maximum stir speed one should aim for is a mere dimple in the surface, nothing stronger than that.

I use lab shakers that make the starters slosh around. Although the agitation is much more "violent" than a stir plate's vortex, the yeast cells are deemed to fare better on the shakers.

I've never noticed any issues with yeast starters coming of a stirrer or a shaker, but haven't done any comparative tests either.

 

[mashdar]

Braukaiser's results indicated faster spin = more cells. He also did staining to determine viability, and did not note any big dropoff.

I have never seen actual empirical evidence for the whole shear force thing. As far as I can tell, it was kicked off by a handwavy blog post, and people who don't want to bother with a stir plate let confirmation bias carry it forth. It's an interesting idea, but the only people I've seen with empirical results all use stir plates.

Re O2 for stir plates, early on the yeast is not producing CO2 and is consuming O2, so solution concentration drops and vortex lets more O2 into solution. Once CO2 ramps up, you're not getting any O2 benefit, but lower CO2 theoretically is less stressful. Braukaiser did find that aerating a stirplate increased yield, but IIRC it was small (10-20%).

 

[ninkwood]

I've been doing this for a handful of batches now, and while obviously anecdotal, I've kept doing it because it leads to the fermentations tend to take off quicker than average and the beers have come out good.

I never even considered that a stir bar could be harming or stressing the yeast, but I wouldn't do my best work if you stuck me on a tilt a whirl for a few hours beforehand!

 

[HighVoltageMan!]

The vortex induces a "shear force" on the yeast cells, which can damage them over time.

I have never seen actual empirical evidence for the whole shear force thing.

Shear force on this level is nonexistent. The amount of force needed is greater than the small stir plate can produced. Yeast shear is more often associated with yeast harvested through a centrifuge. The centrifuge can produce an enormous amount of power and force.

The main indication of yeast shear is a permanent haze cause by the gradual "shearing" of the the cell wall releasing proteins into the beer that cannot be removed with filtering or with clarifiers. I have been using a stir plate for 13 years and I have never had a problem with clarity.

Yeast shear in home brewing is a myth, unless you have a industrial centrifuge.

 

[Broothru]

I have a Maelstrom unit that produces a large vortex on its highest speed setting. With clear water (SG 1.000) at the 1500 ml volume level in a 2000 ml Erlenmeyer using a 1” stir bar, the vortex will reach from the surface of the liquid to the bottom of the flask. But as you pointed out, likely not enough to generate shearing stress on the yeast cells.

With that said, I’ve adopted a mixed process of Shaken Not Stirred that uses an Erlenmeyer with intermittent pulsing on the stir plate. Instead of agitating a Mason jar of starter each random time I pass by it on the counter, I pulse the stir plate for a minute instead. It seems to achieve a more thorough and even mixing, releasing CO2 from the fermenting and the settling yeast/trub.

One thing I think needs mentioning is the release of CO2 from the mix, the elimination of which aids in boosting the efficiency of the process. I keep the vessel open during the agitation to release the CO2 into the atmosphere which is replaced with air (19% O2) that equilibrates with the atmosphere in the flask. Oxygen is necessary for cell growth.

In turn, the agitation in the Erlenmeyer introduces the gaseous O2 into the wort. Any bacteria or airborne yeast or microorganisms are outcompeted by the heathy yeast colony.

At least that’s my theory. I’ve had pretty good luck propagating yeast from frozen, refrigerated, out-of-date, and overbuilt step starters from fresh yeast. In fact there are five going at varying stages right now: one saison, one Kolsch, one lager (all out of date); one Kolsch (frozen); and one Kolsch (fresh, over built). All doing well and throwing off increasing amounts of creamy white yeast.

 

[VTMongoose]

https://www.lallemandbrewing.com/en...and-more/best-practices-rehydration-protocol/

I went down the rabbit hole of yeast rehydration for dry yeasts recently. It seems like based on what I am reading online, rehydration in hot filtered tap water (between 80 and 100°F) containing minerals is likely superior to direct pitching into wort. I have been experimenting with doing this on my recent batches, and they take off significantly faster than either with direct pitching, or with other methods of rehydration I have tried in the past. It seems like it might even be on par with a vitality starter.

The one thing Lallemand does not specify, but I have seen elsewhere - pitch the rehydrated yeast no more than ~30 minutes from the start of rehydration. This seems to be critical.

Usually I'm doing one sachet, 11 grams in 100 mL of water boiled and cooled to ~85°F.

I direct pitch into the chilled wort. I haven't experimented with their relatively laborious procedure of lowering it in 10 degrees increments.

Basically I'm not just seeing a decrease in lag time (time to visible krausen or airlock activity) this round of brews using this method but they also seem to ferment faster. For example my current Dubbel batch 6 fermented with the same pitch rate, yeast strain, and gravity as Dubbel batch 4, is 10 points down @ 24 hours after initial pitch vs 36 hours. Batch 6 hit terminal and was totally done on day 3, where batch 4 was almost done day 3 but crawled for another 2 days. Same pitching temperature of 68 and both hit 80-81 during the free rise. Batch 6 is the new rehydration method. Batch 4 was a 900 mL starter!

It's an n=1 or 2 if I were to dig through my data but I seem to be getting a better pitch rate and fermentation performance this way, possibly just because the viability is better rehydrating in water vs wort. Obviously this is dry yeast specific.

edit: overlayed the data in Excel for those two batches to satisfy my own curiosity. Sorry, inital SG values are a little off because of the calibration of one of my Pills. Ignore the X axis, it's adjusted for time is all you need to know.

 

[Bassman2003]

I wonder if any kind of nutrient or amino acid addition would be beneficial? I add Fermax & zinc to my liquid starters which has really helped with pressure canned wort.

 

[day_trippr]

fwiw, I don't use a lot of dried yeast, but I've always rehydrated dried yeast because when I started brewing ('04) that was the widely recommended method. I've never had to re-pitch, so I figure it works and I keep doing it that way. This Tuesday I pitched rehydrated 34/70 around 5 pm in 58°F wort with a planned free-rise to 65°F, a few hours later it was burping along and by morning it was raging with the wort capped at 65°F...

Cheers!

 

[BrewnWKopperKat]

@VTMongoose : over the past couple of years, Jamil Zainasheff , in a Zymurgy Live and in his new book, is talking about re-hydration for better/superior results.

With a sample size of 2 and BRY-97, I noticed that I got a faster start when I sprinkled the yeast into warm wort (70-75F), moved the wort into my 'fermentation container', and cooled the wort to 65F.

With any anecdotal on dry yeast startup performance, I look for phrases like "the yeast was pitched directly from the fridge" or other indications that the yeast was warm (say 70F) when sprinkled on the wort. Those anecdotal reports are hard to find.

 

[mac_1103]

Doesn't address rehydration, but FWIW - my last two US-05 pitches:

2 packs in ~6 gallons of 1.100 IIPA @ 75F then cooled to 68F - yeast rafts and small bubbles within two hours and vigorous CO2 release within 12 hours.

1 pack in ~5 gallons of 1.050 @ 68F - no discernible activity until almost 24 hours.

 

[Bassman2003]

The dry yeast thing is kind of a mystery. I would consider 68F to be relatively warm. The lag time reported by people is all over the place when by its nature, it should be consistent. A proper test/experiment needs to be made.

 

[BrewnWKopperKat]

Anecdotal stories can lead to curiosity which can lead to useful experiments ...
... but determining what data should be collected can be 'hard'.

The dry yeast thing is kind of a mystery.

It is, IMO, its strain (or SKU) specific.

I would consider 68F to be relatively warm.

Fair point - "warm" is relative to the observer.

The lag time reported by people is all over the place when by its nature, it should be consistent.

I see that also.

I also saw that in "extract is darker than expected" and "can't add flavor salts when brewing with 'extract').

Once I was able to identify the missing data items, it became practical for me to brew with DME to:
1) get color as expected and
2) adjust the DME mineral content to make a good beer better.

A proper test/experiment needs to be made.

What the the missing data items in the anecdotal stories? I have a list of possible items.

If someone is willing "crowd source" the data collection, I'm willing to share those "possible items" for data collection and provide a few data points.