Just how important is aeration?

Yeast & Fermentation
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I recently brewed a beer with OG of 1.072. After I pitched my yeast (2 packets of US-05), I realized I had forgotten to aerate the wort. I was worried when 24 hours later, there was no sign of fermentation. But sure enough, 48 hours later it had taken off and went strong for almost a week. The beer finished at 1.010, which is pretty solid attenuation.

So my question is, what’s the big deal about aerating if my beer is finishing without it?

I guess the fermentation started a bit slower than is usual for my beers, but why does that matter?

Looking forward to your opinions. Cheers!

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Here is the full article from “How To Brew”
http://www.howtobrew.com/section1/chapter6-9-3.html

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Here is the full article from “How To Brew”
http://www.howtobrew.com/section1/chapter6-9-3.html
[/quote]

Thanks, Greg… but I’m familiar with Palmer’s book. Unless you see something I don’t, he doesn’t really discuss what aeration actually accomplishes, other than “Oxygen can be the most significant factor in determining the quality of the yeast.” Okay… why?

If you read what I described, I think it is safe to say my yeast was healthy and fermented very well, without aeration. So, my questions still stand… thanks!

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Well the easy route cam back and bit me in the a$$. :mrgreen:

A more in depth article from Wyeast.

[quote=“Wyeast”]Oxygenation
Oxygen is a critical additive in brewing. Oxygen is the only necessary nutrient not naturally found in wort. Adding adequate oxygen to wort requires a fundamental understanding of why yeast need oxygen, how much oxygen they need, and how to get oxygen into solution and the factors affecting solubility of oxygen.

Why Yeast Need Oxygen

Yeast use oxygen for cell membrane synthesis. Without oxygen, cell growth will be extremely limited. Yeast can only produce sterols and certain unsaturated fatty acids necessary for cell growth in the presence of oxygen.

Inadequate oxygenation will lead to inadequate yeast growth. Inadequate yeast growth can cause poor attenuation, inconsistent or long fermentations, production of undesirable flavor and aroma compounds, and produces yeast that are not fit for harvesting and re-pitching.

How Much Oxygen?

Oxygen requirement is variable depending on: yeast strain employed, original gravity of wort, and wort trub levels.

Some yeast strains have higher oxygen requirements than others. It is generally safe to assume that you need at least 10ppm of oxygen. 10ppm will supply adequate oxygen in most situations. Over-oxygenation is generally not a concern as the yeast will use all available oxygen within 3 to 9 hours of pitching and oxygen will come out of solution during that time as well. Under-oxygenation is a much bigger concern.

High original gravity (>1.065) wort, in addition to increasing osmotic stress on yeast, can cause problems with achieving adequate levels of dissolved oxygen. As the gravity of wort increases, solubility of oxygen decreases. Increased temperatures also decrease the solubility of wort.

The unsaturated fatty acids found in wort trub can be utilized by yeast for membrane synthesis. If wort trub levels are low, yeast will need to synthesize more of these lipids and therefore will require more oxygen.

Methods of Aeration / Oxygenation

Homebrewers have several aeration/oxygenation methods available to them: siphon sprays, whipping, splashing, shaking, pumping air through a stone with an aquarium pump, and injecting pure oxygen through a sintered stone. We have tested all of these methods using a dissolved oxygen meter and have found that, when using air, 8 ppm of oxygen in solution is the best that you can achieve. Injecting oxygen through a stone will allow much higher dissolved oxygen levels. The chart below shows methods tested and the results.

Method / disolved O2 / ppm / Time
Siphon Spray 4 ppm 0 sec.
Splashing & Shaking 8 ppm 40 sec.
Aquarium Pump w/ stone 8 ppm 5 min
Pure Oxygen w/ stone 0-26ppm 60 sec (12ppm)

It was concluded that pumping compressed air through a stone is not an efficient way to provide adequate levels of DO. Traditional splashing and shaking, although laborious, is fairly efficient at dissolving up to 8 ppm oxygen. To increase levels of oxygen, the carboy headspace can be purged with pure oxygen prior to shaking. The easiest and most effective method remains injecting pure oxygen through a scintered stone.

[/quote]

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With dry yeast, there is little to no need for aeration. The reason you aerate is becasue yeast uses the oxygen to synthesize sterols. The sterols promote cell wall flexibility and make cell budding easier, enhancing cell growth. Dry yeast packs contain so many more cells than a liquid yeast that there is little to no need for cell growth like there is with dry yeast. If you pitched 2 packs of 05 into 5 gal. of a 1.072 beer, you have way more than enough yeast cells in there already.

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[quote=“gregscsu”]Well the easy route cam back and bit me in the a$$. :mrgreen:

A more in depth article from Wyeast.

[/quote]

But the OP didn’t use liquid yeast. He used 2 packs of dry.

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Greg - Thanks for following up and will keep that in mind for wet yeast pitching.

Denny - Thanks for drawing the distinction between wet and dry. Very helpful.

I think this makes me biased toward pitching more dry yeast now. It’s cheaper, more cells, stores better/longer, less need of aeration…

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And that’s the reason I primarily use US-05; no starter, no aeration, just sprinkle and bask in my laziness. I may be imagining it, but even when I’ve reused US-05 I’ve noticed that I can get away with aerating less than I do with liquid yeast. Resilient little buggers.

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This is interesting to me. Why, if you didn’t need to aerate using US-05 the first time, would you need to aerate using the second time? Even though I didn’t aerate when I pitched, it’s safe to say the yeast reproduced and there is now more cells than I began with. Assuming I washed and repitched the whole cake, would you recommend aerating? Seems like if I had enough cells the first time, I should certainly have enough cells the second time…

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This is interesting to me. Why, if you didn’t need to aerate using US-05 the first time, would you need to aerate using the second time? Even though I didn’t aerate when I pitched, it’s safe to say the yeast reproduced and there is now more cells than I began with. Assuming I washed and repitched the whole cake, would you recommend aerating? Seems like if I had enough cells the first time, I should certainly have enough cells the second time…[/quote]

I would not recommend repitching the entire slurry into 5 gal. of anything less than a 1.100 brew. Use part of it. For me, 1/3 to 1/2 of it is just right.

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This is interesting info!

It was concluded that pumping compressed air through a stone is not an efficient way to provide adequate levels of DO. Traditional splashing and shaking, although laborious, is fairly efficient at dissolving up to 8 ppm oxygen. To increase levels of oxygen, the carboy headspace can be purged with pure oxygen prior to shaking. The easiest and most effective method remains injecting pure oxygen through a scintered stone.

I’m looking to buy some new equipment and have been going back and forth between aeration, beer gun, perlick taps. I’m pretty sure I’m going with new taps and reading this makes me feel better about still shaking the carboy for aeration. I also use a mix/stir wine degasser.

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Right, I wouldn’t actually use the whole slurry. More trying to get at the question:

I have more yeast cells after the first fermentation than I did before. If I didn’t have to aerate in round 1 to increase cell count, why would I have to aerate in round 2 (assuming I pitched enough)?

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Right, I wouldn’t actually use the whole slurry. More trying to get at the question:

I have more yeast cells after the first fermentation than I did before. If I didn’t have to aerate in round 1 to increase cell count, why would I have to aerate in round 2 (assuming I pitched enough)?[/quote]

A couple things that come to mind, based more on what I’ve read than personal experience, so take it for what it’s worth (ie, not much). Dry yeast is supposedly healthy yeast packed with nutrients for storage and then reactivation, so aeration becomes a redundant step. When you reuse dry yeast, it behaves more like liquid yeast, and no longer has the “packaging”. Since it’s now used liquid yeast, there’s likely a spectrum of yeast health in the slurry, so aeration helps to make sure the bulk of the yeast are healthy and ready to go to work. I suppose if you’re using up to half the slurry, you probably do have enough healthy buggers to go to work even without aeration.

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My personal experience with inadequate aeration is that there is little effect on the beer being fermented if sufficient yeast is pitched. However, I typically harvest my yeast and end up using it for several batches, and if a batch of yeast is forced to work through a fermentation without the wort being oxygenated properly, it will not work well in subsequent batches.

So if you don’t plan to reuse the yeast, you can pitch either dry or a sufficiently sized starter of liquid yeast and be OK.

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The reason your beer was successful is the amount of yeast you pitched, enough that it didn’t need to rely on reproducing to convert sugars.
A factor that influences the fermentation and enhances biochemical processes is wort aeration. Oxygen presence in the initial phase of fermentation is essential for fast yeast reproduction and full sugar restoration. Correct aeration improves biomass vitality and yeast cells’ immunity to different stresses owing to the maintenance of the correct amount of glycogen and trehalose. As a result, yeast is able to perform a selective exchange of metabolites and extract nutrients from the environment. A low amount of oxygen in the wort may cause fermentation delay or slow primary fermentation or produce larger amounts of undesired components in the new beer aroma such as acetaldehyde and vicinal diketones.

Yeasts require appropriate quantities of oxygen to synthesize unsaturated fatty acids and sterols, both of which are needed for continued anaerobic growth and cell division. As the fermentation rate is proportional to the number of metabolically active yeasts present, rapid wort attenuation is therefore related to the availability of oxygen. The effects of limited oxygen supply are compounded in high gravity or very high gravity wort fermentations 2.

Biomass aeration promotes sterol synthesis in the cell wall 3. Sufficient oxygen availability for yeast, especially at the beginning of the fermentation process, also relates to lipid synthesis, which is inhibited as long as fatty acids and, consequently, esters are being produced 4. Yeast will not bud when sterol levels are too low. This means that, while yeast operates anaerobically, it still requires oxygen for successful fermentation.
.

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Sadly most of those guys aren’t around anymore.

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