Purpose of wort oxygenation

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timbudtwo

timbudtwo

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I was trying to figure out what the actual purpose of oxygenation was and I can't really find anything other that it just kick starts the yeast.

When oxygen is available, yeast can use the oxygen to completely oxidize the sugar and the resultant waste is CO2 and water. However, in an anaerobic environment (where there is no O2) the yeast produce CO2 and ethanol but produce less energy in the reaction.

Wouldn't making a larger starter be easier / better than adding oxygen to the wort, especially if you are going for a high abv beer?
 
When you have an aerobic environment, the yeast cells multiply, dont they? That would give a larger number of actual yeast cells. You could do a larger yeaststarter and accomplish the same thing i would think. I am no yeast expert and am drawing my knowledge from reading stuff. I don't know if I am entirely accurate or not.
 
Aerobic environment = yeast can process sugar into energy more efficiently, no alcohol production, mitosis (more yeasties) occurs

Anaerobic environment = yeast cannot completely process sugar and produce CO2 and Alcohol as waste at the expense of not getting as much energy out of the sugar, mitosis still occurs.
 
I think this pretty much says it all... First section covers why, the rest of the info is just gravy... :D

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 DO 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.
 
Golddiggie
Large Member

HAHAHAHAHA!!!! Thats funny. Anywho, YAY!!! I was somewhat right. Reading these forums has absorbed into my brain a bit. Now if I could just download the entire forum to my brain via bluetooth. Got an app for that?
 
djsethall said:
...now if I could just download the entire forum to my brain via bluetooth. Got an app for that?
Click to expand...

"tank, I need an up-link."

haha.

but seriously... I was actually thinking the same exact thing as the OP since my last brew (imperial stout/stout PG). If oxygenating your wort is done to help yeast multiply, seems like this would be moot if you already had enough cells in your starter.
 
Golddiggie said:
I think this pretty much says it all... First section covers why, the rest of the info is just gravy... :D

Why Yeast Need Oxygen
Yeast use oxygen for cell membrane synthesis....
Click to expand...

What he said.
But one point you made.
It is about having enough healthy (lots of good membranes) yeast at the beginning of the ferment. Strictly speaking, if they yeast were grown up in a high O2 environment in the starter (oxygenated, stirred, low carbs added continuously) - and this is possible in a commercial environment, then there is no need to oxygenate the actual wort. However for the hombrewer it is easier to just oxygenate the wort than to build a bioreactor to grow up the yeast.
 
mmmmm... bioreactor... eeeexxcellent (wrings hands together sinisterly)


so does the mrmalty pitching calculator take into consideration aerated vs. non-aerated wort?
 
HItransplant said:
mmmmm... bioreactor... eeeexxcellent (wrings hands together sinisterly)


so does the mrmalty pitching calculator take into consideration aerated vs. non-aerated wort?
Click to expand...

No. You should always aerate your wort before pitching.

From How to Brew by John Palmer

howtobrew.com said:
Chapter 8.1.3 - Temperature Factors

8.2.1 Lagtime or Adaptation Phase

Immediately after pitching, the yeast start adjusting to the wort conditions and undergo a period of high growth. The yeast use any available oxygen in the wort to facilitate their growth processes. They can use other methods to adapt and grow in the absence of oxygen, but they can do it much more efficiently with oxygen. Under normal conditions, the yeast should proceed through the adaptation phase and begin primary fermentation within 12 hours. If 24 hours pass without apparent activity, then a new batch of yeast should probably be pitched.

At the beginning of the adaptation phase, the yeast take stock of the sugars, FAN and other nutrients present, and figure out what enzymes and other attributes it needs to adapt to the environment. The yeast use their own glycogen reserves, oxygen, and wort lipids to synthesize sterols to build up their cell membranes. The sterols are known to be critical for enabling the cell membrane to be permeable to wort sugars and other wort nutrients. Sterols can also be produced by the yeast under poor oxygen conditions from lipids found in wort trub, but that pathway is much less efficient.

Once the cell walls are permeable, the yeast can start metabolizing the amino nitrogen and sugars in the wort for food. Like every animal, the goal of life for the yeast cell is to reproduce. Yeast reproduce asexually by "budding". Daughter cells split off from the parent cell. The reproduction process takes a lot of energy and aerobic metabolic processes are more efficient than anaerobic. Thus, an oxygen-rich wort shortens the adaptation phase, and allows the yeast to quickly reproduce to levels that will ensure a good fermentation. When the oxygen is used up, the yeast switch metabolic pathways and begin what we consider to be fermentation - the anaerobic metabolism of sugar to alcohol. This pathway is less energy efficient, so the yeast cannot reproduce as proficiently as during the adaptation phase.

The key to a good fermentation is lots of strong healthy yeast- yeast that can get the job done before going dormant due to depleted resources, rising alcohol levels, and old age. As noted, the reproduction rate is slower without oxygen. At some point in the fermentation cycle of the beer, the rate of yeast reproduction is going to fall behind the rate of yeast dormancy. By providing optimum conditions for yeast growth and reproduction in the wort initially, we can ensure that this rate transition will not occur until after the beer has become fully attenuated.

Worts that are underpitched or poorly aerated will ferment slowly or incompletely due to lack of viable yeast. Experienced brewers make a big point about aerating the wort and building up a yeast starter because these practices virtually guarantee enough yeast to do the job well.
Click to expand...

Source: http://howtobrew.com/section1/chapter8-2-1.html
 
Yes, you could pitch enough yeast that the cells would not need to grow to ferment the wort. What would most likely occur, would be yeast autolysis, and an undrinkable beer, because some yeast growth will occur anyway, and a given wort can only provide enough nutrients for a limited population of yeast.

Ideally, you want each cell pitched to bud 2-3 times, which means you need enough sterols for the yeast to be able to bud that many times, and enough nutrients available (yeast available nitrogen) for the cells to synthesize enough proteins to produce the ideal number of offspring. Yeast cannot produce sterols without O2 present in the wort.

Higher gravity fermentations benefit from the introduction of O2 in stages during the growth phase, so that yeast cells which have already budded can replenish the sterols they gave up to their daughter cells. This keeps the cell walls flexible, and thicker, allowing the yeast to counter the higher osmotic pressure from the remaining wort sugars, as well as higher ethanol concentrations later on. In other words, O2 will help the yeast ferment to a higher %ABV.
 
Saccharomyces said:
Yes, you could pitch enough yeast that the cells would not need to grow to ferment the wort. What would most likely occur, would be yeast autolysis, and an undrinkable beer, because some yeast growth will occur anyway, and a given wort can only provide enough nutrients for a limited population of yeast.

Ideally, you want each cell pitched to bud 2-3 times, which means you need enough sterols for the yeast to be able to bud that many times, and enough nutrients available (yeast available nitrogen) for the cells to synthesize enough proteins to produce the ideal number of offspring. Yeast cannot produce sterols without O2 present in the wort.

Higher gravity fermentations benefit from the introduction of O2 in stages during the growth phase, so that yeast cells which have already budded can replenish the sterols they gave up to their daughter cells. This keeps the cell walls flexible, and thicker, allowing the yeast to counter the higher osmotic pressure from the remaining wort sugars, as well as higher ethanol concentrations later on. In other words, O2 will help the yeast ferment to a higher %ABV.
Click to expand...

I see... does this also explain why we dont want to overpitch

thanks for the thorough education. I plan on picking up "yeast," will I learn more about this from reading it?
 
HItransplant said:
now that makes sense.. so you want another generation of yeast once pitched because it is better suited to the actual wort you want it to ferment (as opposed to the starter wort).

am I understanding this?
Click to expand...

With all due respect to Palmer,
His text is an excellent one for the beginner and intermediate brewer but for the sake of clarity and brevity he is forced to simplify a number of technical points.

I would be grateful if you could quote a primary source who shows that oxygenation during growth of pitching yeast gives inferior results to oxygenation of the bulk wort. However I don't feel that assertion is true. There is no plausible mechanism for wort oxygenation to be a superior approach.

The yeast does not have to "adapt" to the wort in which it is fermenting if it is already in log phase. The statement presumes the use of dormant yeast which the brewer may be using from a dry pack or from a smack pack.

Not to pick nits but I just want to make it clear that a cell with an ideal plasma membrane can easily do 3-4 generations before running into trouble with autolysis. Given an ideal large population of yeast cells, the wort would not require oxygenation.
 
If you over-pitch (somewhere around final amount of yeast), and not a "normal sized" starter, you will not need the yeast to reproduce. This lack of reproduction will change the amounts of yeast by-products and metabolites produced. For some beers this would be a benefit, but for most I would say that would be detrimental.

I would not say that any one method is better than another, but it seems that if you are looking for yeast flavours while saving money at the same time, then the normal rates of 1million cells/*P and 8-12 ppm O2 is a good compromise. You can use a larger starter, but it requires more expense in materials/flasks and only saves you the expense of either some elbow grease (pouring between buckets) or an aquarium pump and a sterile filter. You can go with a lower pitch rate (lots of new brewers seem to think that the Wyeast "propogator" packs are ready to pitch), but you risk a stuck fermentation and under-pitching off-flavours.

I guess what I am trying to say is that the pitching/oxygenation rates are not theoretically derived, they are based on observations of flavours and fermentation characteristics. If you feel that your recipe requires the use of a different set of pitching/oxygenation rates then go for it! That is the beauty of homebrewing. You get to try and outsmart what all of the commercial resources say is the "best" way of doing things. That is what science is after all!
 
Most of us use the 'Activator' pack from Wyeast since that CAN be pitched directly without issue (depending on the wort OG). Propigator packs say to use a starter beforw pitching into a brew.

I picked up an O2 system from Williams Brewing and have used it on two batches so far. I plan to continue to use it and see how the brews come out with it in the mix. Since you can only get above 8ppm of O2 with actual O2 it means I have a more capable oxygenation system.
 
theredben said:
If you over-pitch (somewhere around final amount of yeast), and not a "normal sized" starter, you will not need the yeast to reproduce. This lack of reproduction will change the amounts of yeast by-products and metabolites produced.....
Click to expand...

Point taken. And I agree that your product will vary based on which path you take. I just wanted to get the point across that there was nothing particularly magical in putting oxygen directly into the wort (Hey that's what I do when I homebrew). But, oxygen is very important at some stage in the yeast lifecycle for them to build the structures they need to survive and thrive.

Let's face it, most historical brews before the end of the industrial revolution did not utilize oxygenated wort. Some brewers would add air during the first few days of fermentation (some British Ale breweries).

PS I note you are in Langley. Do you ever get out to a Vanbrewer's Meeting?
 
Not sure how a 1 sentence answer is data. Seems like all you were looking for was a fancy sounding response to oxygenation concerns.
 
theredben said:
Not sure how a 1 sentence answer is data. Seems like all you were looking for was a fancy sounding response to oxygenation concerns.
Click to expand...
Wow, really? What's with the hostility?

Sounds like you need to learn to be a Berean. Throw that phrase into google and prepare to be overwhelmed with actual facts of why oxygen is needed.

Acutally, here, ill do the work for you:
http://www.wikipathways.org/index.php/Pathway:WP343
Please look at the sections where O2 is required for a reaction.

Then, go look at what Ergosterol does and what it is for. It does for fungus what cholesterol does for humans. It allows for proper permeability of cellular membranes.

That "fancy sounding response" allowed me to actually learn something useful and factual, rather than just a bunch of well written and sourceless press releases.
 
My point was that in a forum labelled "Brew Science" it should be required to give more than just a sentence to respond to statements made. While I understand that oxygen is literally required for yeast growth, what I question is the amounts required to make good beer. Remember that we are brewing beer here, not looking for optimal yeast growth.

I am not interested in biological pathways, I am interested in fermentation in homebrew situations.
 
theredben said:
I am not interested in biological pathways, I am interested in fermentation in homebrew situations.
Click to expand...

For the most part, that has been relatively well covered. The general consensus is "it will be different for every batch of brew."

I was trying to figure out whether or not it was super necessary. A lot of the time you find information that says to do one thing or the other. Don't use aluminum pots = total bs. Don't squeeze the grain bag = total bs. People say you MUST oxygenate your wort, well why?

I now know the reason for oxygen addition, and I have proof that chemicals necessary for the reproduction of yeast cells are produced aerobically. None of this hear-say old wives tale crap.

I get tired of anecdotal evidence. Good for cuts and scrapes, but for something that I want to get better at I prefer hard facts.
 
timbudtwo said:
I get tired of anecdotal evidence....
Click to expand...

I completely get where you are coming from. Its just when writing to a forum, what may seem witty or "to the point" on one end can look hostile on the other.
Generally the discussions on this forum have been congenial even when heated.
;) (emoticons help)

One of the biggest problems that the homebrewer faces is trying to translate not only purely biochemical data (which doesn't always translate to real life as expected) AND deal with commercial brewing data (which doesn't always scale properly to the homebrew environment - eg Hot Sided Aeration) AND deal with the great weight of completely unfounded brewing tradition.

The best part of the "Brewing Science" subforum has been the willingness of a number of participants to actually write up properly controlled experiments that showed real results at the scale that we were interested in.

So who wants to step up and run a 5gallon oxygenation trial?
:D
 
It's been done. Pretty tightly controlled experiment.

Reelale said:
Here's some more info that I posted in an earlier thread that uses actual flow rates. I found it quite interesting.

Interesting discussion of wort oxygenation techniques

Saw this on hbd.org and thought some would be interested in it here. I couldn't link directly to the discussion, but if you go here it can be found http://hbd.org/cgi-bin/discus/discus.cgi.

This post is in response to some recent discussions regarding oxygenation levels in wort.
We (Wyeast) recommend 8-15 ppm O2 for healthy fermentations. Some strains require higher oxygen levels than others. Manipulation of pitch rates can increase or reduce the need for oxygen levels. High pitch rates lead to fewer doublings and reduce the need for high levels of sterols. Sterol levels are typically the limiting factor in cell growth. These cellular membrane components are synthesized by the cells using oxygen during the lag phase and assist in keeping the membrane flexible and permeable. Low pitching rates lead to an increase in cell growth (doublings) requiring higher levels of sterols and oxygen.

Last year I ran an experiment comparing homebrew oxygenation methods. The experiment compared dissolved oxygenation levels achieved vs. time for homebrew oxygenation methods including splashing and shaking, siphon spray, aquarium pump, and pure oxygen. I presented the results at the NHC last year in Vegas.

Methods Compared:
Splashing and Shaking- Traditional homebrew aeration method of picking up the carboy and shaking it.
Siphon Spray - Small attachment to your run-in hose that splashes the wort as it enters the fermenter.
Aquarium Pump and Stone- Running compressed air from an aquarium pump through a 2 micron stone (Oxynater).
Pure Oxygen- Running Oxygen through a 2 micron stone (Oxynater) at a flow rate of 3.5 LPM.
The same wort and temperature was used for all methods. Dissolved oxygen levels were measures at 5 second intervals using a DO meter.
OG- 1.045
Temp- 68 F
Volume- 5 gal
Fermenter- Standard 5 gal glass carboy
Stone pore size- 2 micron (Liquid Bread Oxynater)
Oxygen Supply- Bernzomatic
Oxygen flow rate with Bernzomatic was estimated at 3.5 LPM based on a visual comparison of stone activities (vigor of bubbles) with a regulator with gauges on a larger cylinder.

Results:
Siphon Spray: Delivered 4 ppm in wort transfer.
Splashing and Shaking: Reached saturation point of 8 ppm in 40 seconds.
Aquarium Pump and Stone: Reached 8 ppm in 5 minutes.
Pure Oxygen with Stone: 8 ppm (20 seconds), 15 ppm (80 seconds), 22 ppm (2 minutes)

Comments:
There are a lot of variables involved with dissolving oxygen into solution including wort gravity, wort temperature, stone pore size and surface area, O2 flow rate, time, turbulence of wort, and fermenter geometry. This experiment attempted to reduce the number of variables. Oxygenation of a large amount of liquid with a small stone is not an efficient way to dissolve O2 into solution, but in most homebrew cases it is the only method available. Oxygenation in-line (professional method) increases surface area and contact time and increases the efficiency of dissolving O2.
That being said, this experiment demonstrated that using an aquarium pump with a stone is not an efficient way to deliver oxygen into wort. Splashing and shaking was rather efficient (40 sec.) in achieving O2 saturation point with air. Pure oxygen is an easy method that not only allows brewers more efficiency and better control over DO levels but also allows brewers to attain higher levels of DO versus using air.

As a side note, I currently use a combination of two methods. I inject a small amount of O2 and then shake my carboy to fully dissolve it into solution. I have not run any tests with this method but am confident that I am achieving good levels of DO.

I hope that this helps. If you want any additional information or a chart on oxygenation levels vs. time using O2, please email me at [email protected]

Thanks,
Greg
Click to expand...
 
giligson said:
I completely get where you are coming from. Its just when writing to a forum, what may seem witty or "to the point" on one end can look hostile on the other.
Generally the discussions on this forum have been congenial even when heated.
;) (emoticons help)
Click to expand...

I know, I know. No fighting on the internets. Just his comment irked me because I actually found something useful from that comment and it was returned with a wry statement.

To the above poster,
Thanks for putting it in here for relevance. Good info.
 

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