Aeration and starters

[Kealia]

Yesterday I whipped up a quick 6G batch of the Brew Demon One Evil Pilsner to take to an office holiday party around Christmas time.
It's been a LONG time since I made an HME batch so while the process was quick, I was a bit rusty.

Case in point: I made a starter the day before for my WLP001 and pitched it at high krausen. A few hours later I realized that I didn't aerate the batch (other than what minor aeration occurred during the pour from the kettle into the bucket). It got me thinking....

If the main purpose of oxygen in the wort is for yeast health (growth, etc.), is it really necessary if you have a starter that you pitch at high krausen?
I guess it comes down to whether or not the yeast are still continuing to grow when you pitch them into the wort, or if you are pitching the right amount and zero growth occurs at the time of pitching.

I'm not worried at all about this batch but it definitely made me think about this in the more philosophical sense.

So, what say ye on this topic. I'm really curious to get some opinions on this.

[FedoraDave]

I've thought about this myself, and here's what I think:

Boiling removes oxygen. That's why it bubbles and rolls when it boils. It's also why, if you boil water, let it cool, and then drink it, it tastes "flat" and flavorless.

So even if you've got a healthy krausen, you're pitching it into wort that's had some of the oxygen boiled out of it. I'm sure the yeast will still do the job, but it might take longer. Still, if you poured the wort from the kettle into the bucket, that will certainly aerate it to some degree.

[Kealia]

Yeah, like I said I have no doubt this batch will be fine. The question becomes "is it still necessary/recommended to aerate if you're pitching a starter at high krausen?"

One could argue that because you've already grown the yeast there is no need to aerate the wort.

[Beer-lord]

Back in the day I never even knew about aeration and never really had a problem. Back then my beer wasn't great, just ok but it wasn't the fault of the yeast but the so-so ingredients.
I think good, healthy yeast do just fine with no aeration. If you do it, that's great but if you forget it, I wouldn't worry about it.
I've had beers that I did everything I've read I'm supposed to.....water adjustments, aeration, long boils, yada, yada, yada and they sucked. Then there were others I really messed up but they came out fine. Go figure. It sometimes up to the beer gods.

[mashani]

There isn't 0 yeast growth after you pitch unless you massively overpitch.

See this:

http://www.archive.maltosefalcons.com/t ... turing.php

Search for "Stages of Yeast Growth" and you will find a chart. Even with a proper starter you are going to see growth. The synopsis which applies here is this (see below). And you WANT this to happen, because the esters and/or phenols produced are important to round out the beer - even in a "clean" beer there are still subtle esters.

"III) The third phase is the exponential phase where yeast reproduction and metabolism is in high gear. Cells are dividing every 90 - 180 minutes and fermentation begins. During this time the number of yeast cells may increase as much as 1000-fold (or 3.0 logs) within 24 hours. The extent to which the cells divide is dictated primarily by the pitching rate. If appropriate pitching rates are used, the yeast are pitched at high concentrations (5-15 million yeast cells per ml) and undergo approximately 3 generations (23- or an 8-fold increase in cell number) to yield 80-100 million cells per ml. 100 million cells per ml is about the maximal concentration of yeast attainable in fermenting wort (Figure 2 ∓ 3). Fermentation is also very active and a krausen may be beginning to form.

IV) The fourth phase is the decelerating growth which should occur 12-24 hours after pitching. At this time the oxygen is fully depleted and fermentation and CO2 production is taking over. Fermenting wort should be in high krausen. Maximal fermentation occurs during 12-48 hours; heat is being generated and there should be rapid CO2 evolution (bubbling)."

EDIT: So anyways, if you pitch with a starter then sure less oxygen is needed because less cell division is required. A lot of it happened in the starter. But it is going to grow a lot more still - so you still should have a good bit of oxygen in there because the cells need it to build healthy (not mutant) versions of themselves, and your talking about a stupidly large number of cells. But if you pitch a starter at high krausen you are also pitching a bunch of oxygenated wort into there too, so you are adding oxygen. So how much you really need to aerate, I don't know but probably some is probably still a good idea for optimal fermentation.

[Gymrat]

Pouring from kettle to bucket, if you do so vigorously, will aereate your wort a lot more than you can by stirring it. You should be fine.

[ScrewyBrewer]

Making a starter also acclimates the yeast to the wort environment so it can hit the ground running and absorb nutrients without being shocked by an environment it's not used to. If done correctly on a stir plate a starter should more than double the yeast's packaged cell counts. The pitching rate calculators already take into account that the, overall inoculation rate needed to ferment a wort at a given gravity, is based on the cell count initially pitched.

It's easier to describe the growth rate of yeast during fermentation as, the amount of yeast left in the fermentor after the beer has been emptied from it, compared to the amount of yeast pitched. As for the relationship oxygenation plays in a starter when pitched into wort that wasn't oxygenated, that's a bit more difficult to describe because a lot has to do with the gravity of the wort, the attenuation rate of the yeast and the number of cells required to ferment the beer down to it's expected final gravity.

Yeast has two sets of pathways one aerobic when the wort is loaded with oxygen and the cells are building up energy and the other anaerobic when the oxygen is gone from the wort and fermentation begins in earnest. That's why oxygenating wort before pitching your yeast is recommended for beers 1.060 or higher, because alcohol tires yeast out, requiring more cells to ferment the same volume of beer. I guess it's not that easy to respond with a one size fits all answer to a very straightforward question, there's just too many other variables to consider that will sway the reply.

[gwcr]

I know this is a dry yeast and as such doesn't need a starter, but wanted to share this tidbit from the Danstar BRY-97 data sheet.

"BRY-97 American West Coast Yeast has been conditioned to survive rehydration. The yeast contains an adequate reservoir of carbohydrates and unsaturated fatty acids to achieve active growth. It is unnecessary to aerate wort."

My guess is as the yeast cultures continue to improve and evolve, that it will be less important to aerate. Can't imagine it would ever do any harm to aerate, just that it may not be a necessary step in the future.

Danstar BRY-97 Technical Data Sheet

[jimjohson]

Assuming you make HMEs like me, and only heat the water to the desired temperature. The air's going to be a mite thin, so to speak, but there's probably just enough.

[mashani]

I know this is a dry yeast and as such doesn't need a starter, but wanted to share this tidbit from the Danstar BRY-97 data sheet.

"BRY-97 American West Coast Yeast has been conditioned to survive rehydration. The yeast contains an adequate reservoir of carbohydrates and unsaturated fatty acids to achieve active growth. It is unnecessary to aerate wort."

My guess is as the yeast cultures continue to improve and evolve, that it will be less important to aerate. Can't imagine it would ever do any harm to aerate, just that it may not be a necessary step in the future.

Danstar BRY-97 Technical Data Sheet

This is true for all modern dry yeast strains AFAIK. It is an advantage of dry yeast that helps make it easier to use. This is why they tell you not to make starters with them.

But this can't be done for liquid yeast that I am aware of. It's something that happens with the process they use to create the dry strain, and my impression is that not all the liquid strains can handle this process.

And if you were to wash and re-use that dry yeast later you would want to make a starter and aerate.

[Kealia]

Thanks all for the thoughts so far.

Dave, thanks especially for your detail - that was the heart of what I was looking for. I guess I somewhat assumed that if you made a starter and pitched at high krausen that you had the right number of cells to ferment - which isn't really true. What you have is the right amount of cells to PITCH to allow for the growth that still needs to occur in the wort. I was thinking that a starter got you all the cells you needed and they "skipped" the growth phase after being pitched but that's not true. The optimal PITCH rate is to ensure the optimal growth rate and conditions, it doesn't give you the full number of cells needed to ferment.

So yeah, I'm not concerned with this batch as I had some minor aeration from pouring the wort in and the 3G of pre-chilled (non-boiled) water contained some oxygen, as did the starter.
What I've done is not optimal, but will still produce good beer. I have another can of the HME left that I'll use at some point and I will remember to aerate properly.

Cheers.

[mashani]

Yep, that is why I say that even a huge underpitch will still ferment out, given enough oxygen and nutrients in the wort. It's why 2g yeast packs Mr. Beer sold were "enough" to make beer. The yeast end up growing more generations in the wort, but they still will grow to approximately the same level *if* you have enough oxygen and nutrients to support the growth. Once they run out then they are forced into a different phase of fermentation. That's where lack of cells can start to hurt, so especially if underpitching a good amount of oxygen is needed.

Extending the growth phase just tends to produce more esters. Might be bad in a clean style, but it can be a good thing in a wheat beer where you want banana. Underpitch is perfectly valid technique for that. I think pitch rate calculators actually fall on their face when it comes to wheat beers where you want Banana, or some types of Belgians where you want the fruity esters to shine because they tell you to pitch too much in that case where some extra generations of growth are "good" for what you want. If you overpitch a wheat you can end up with no banana or very tart beer depending on the yeast strain.

This is also why if you over oxygenate your wort, IE you use pure oxygen and let it rip, you can actually extend the growth phase and not see krausen for a longer time then if you didn't oxygenate depending on your pitch rate.

Hope that all made sense.

[Kealia]

Yeah, I'm good on that part of the knowledge - I guess I just wasn't connecting the dots on the growth part in relation to a starter.

[FedoraDave]

This topic is interesting to me as it relates to the batch I brewed Sunday.

It was a 2.5 gallon batch, using dry yeast (Mangrove Jack M44). I rehydrated the yeast at around 90 degrees just before flame-out, so it had a good 15-20 minutes at least while I was chilling the wort. For the smaller batches, I cool the wort with cold water baths in the sink, because I don't want to be bothered with an immersion chiller. I stir the wort with a whisk while I circulate the water in the sink, replacing the water as it equalizes with the wort temperature.

The wort is aerated thoroughly as a result. I usually have foam overflow when I rack to the carboy via a funnel. With this batch, I also used a wine degasser powered by my cordless drill to aerate after pitching, as I do with my five gallon batches.

This batch only began to take off late last night, over 30 hours after pitching. It's doing fine now, but it just was slow to get started.

It happens.