Help me better understand the concept of oxygenating wort...

[davidgsmit]

So I just brewed a big RIS that'll come in at just over 10%. I don't have an oxygen bottle or even a pump and filter to inject regular air into my wort. Before I invest in such equipment I'd like to clarify a few things:

My understanding is that the reason we add oxygen into the wort is so the yest can create fatty acids needed for cell growth. I've tried the olive oil technique (no aerating but rather adding a drop of olive oil) and this seems to work without any problems. For some reason though, I just tend to prefer the age old traditional method of adding oxygen as it seems more legitimate I suppose.

I also understand that wort does not hold on to the vast majority of the O2 we introduce for more than 30 min or so (If memory serves me right). So with that in mind, why do we need equipment to introduce as much O2 as possible if most of it comes right back out again? Seems to me that 30 min is far too short of a time span for fresh pitched yeast to take much advantage of.

So here's my real question: I shook up my wort before adding the yeast. I'm guessing I'll need to add more O2 to the mix to get to my target gravity; is this because they yeast will run out of the fatty acids at some point? I wonder if I were to just add a drop of olive oil if that would prevent me from needing to aerate further?

All this also makes me wonder if oxidizing your beer isn't a way overblown concern as long as your yeast is still relatively active. If the wort loses most of the O2 in such a short time frame it seems that I could probably wait a week, then rack my RIS and shake it up again without risking much. My intent at this time is to wait another day or two, take off 3/4 of a gallon and shake that up, then reintroduce it into the wort; effectively limiting how much O2 can be absorbed.

All that said, what are the thoughts and experiences of the HBT community on these variables? Is there anybody out there who exclusively uses olive oil and has done so with a big beer? How do you personally manage the continued fermentation of a big beer with regards to the oxygen?

Thanks all!

 

[ncbrewer]

Here are a couple of links that might help:
https://www.homebrewtalk.com/f128/olive-oil-testing-388924/
https://www.homebrewtalk.com/f13/using-olive-oil-instead-oxygen-47872/

 

[cervid]

There's a big difference between adding oxygen to wort before it has fermented, or even in the beginning phases of fermentation than post fermentation.

You only need to oxygenate your wort before pitching. After that, you don't want to do it, you want the anaerobic fermentation at that point.

This is different than making a starter for instance. You want a starter to be oxygenated the whole time. You goal is maximum production of healthy yeast. With beer, you are pitching said healthy yeast into something you are trying to produce the best flavors in. It's the same reason you ferment at lower than 90-100 degree temperatures, which is really around the temp brewer's yeast likes the best.

Even old school methods where the fermenting wort would get roused is done in an environment where there is only CO2 in the wort. Rousing or shaking it won't add O2, unless the fermentor isn't airtight. You might get some of the liquid from you airlock to suck back in, but I've only had this happen in my PET fermenter. Also, I mostly use blowoffs for the first few days until I need to sample or sometimes keep it on the primary the whole time.

I think oxidized beer is overblown if you drink it quickly, which I always seem to do. If you let it age a while, that would be amplified. You can find some info out there on oxygenation. I think actively introducing oxygen to the wort anytime after pitching the yeast is probably not a great idea. I have read a lot about brewing and have literally never heard of anyone attempting to introduce O2 to their wort during fermentation, ever. I've done it with mead, many others do, but that is a totally different environment.

I've always oxygenated the wort before pitching and I've never had a stuck fermentation, yet. Although I also always pay attention to my pitching rates.

The bottom line is, as long as you pitch enough yeast, you'll be fine. You shouldn't be introducing O2 during fermentation in an attempt to make up for a stuck ferm or because you under pitched. You would need somewhere around 300-400 billion cells for that brew in a 5 gallon batch, just going off the top of my head and assuming your OG and batch size.

I can't speak as to personal experience with Olive Oil. I've never tried it, and really haven't seen the need to. Plus, considering unless you are buying really great olive oil, it's probably not olive oil anyway. I think they are just now coming out with standards for olive oil, but that industry has been pulling one over on us for a long time.

 

[oldschool]

I also can't comment on the use of olive oil except I know that it has been done successfully.
In regards to oxygen for fermentation. Yeast would much rather undergo cellular respiration instead of fermentation. Cellular respiration(oxygen present) yields 28 ATP for every molecule of glucose which gives the cell enough energy to manufacture their cell membrane and sends acetyl co A in to sterol production mode. Sterols are needed for cell membrane integrity and health. When you pitch yeast in to oxygenated wort they will use up 100% of it in 30 minutes time.
Fermentation (without oxygen) yields 2 ATP for every glucose molecule so you can see why they would rather their be oxygen present. When the oxygen runs out acetyl co A gets put to use manufacturing esters so that is one way to control ester production. No oxygen = no cell growth. You need growth for flavor production and to build up enough healthy cells to finish the fermentation process. Some people add oxygen to the wort a second time about 12 to 18 hours after the initial oxygenation and yeast pitch but that is just for highly concentrated worts. They wait that amount of time to let the yeast go through at least one doubling then add more oxygen to give them a second round of growth. With everything you do there is some sort of effect so just keep that in mind. With a beer as big as what you are talking you really should use pure oxygen due to the low solubility of high gravity worts. Without buying an O2 setup I would say your best bet is to pitch another slurry of actively fermenting yeast if you think they are going to have a hard time reaching terminal gravity.

Hopefully that clears up some of the oxygen confusion. Someone correct me if I got something mixed up.

Cheers

 

[davidgsmit]

Oldschool; That was my thought exactly... I don't see the harm in adding some o2 within the first 48hrs, especially not with a beer that'll take a good while to ferment. If I pull off a half gallon or so, it can only absorb so much 02. Add that back in and the yeast will use it up quickly, multiply a bit more, and get right back to making esters, etc, except with a higher count. Am I missing something here?

NCBrewer; I think I've read through both of those threads completely in the past, hence my trying out the olive oil to begin with, and it does indeed work. I've read that New Belgium tried it once or twice on a commercial batch, but I believe they went back to o2. Not sure if there was a good reason to go back to o2 or not. I will send them an email and inquire about that.

Cervid; You make a number of good points, although I'm really stressing adding only a controlled amount of o2 early in the fermentation. Your point is well taken when it comes to adding o2 later in the fermentation or on an ongoing basis, but I'm not so sure I agree with your concerns if we're simply talking a relatively small amount in the first 48hrs or so.
I have actually heard of a brewery that adds o2 in their big beers... Wayne at Cigar City uses this technique and I'd have to argue it doesn't seem to be negatively impacting the beers they're putting out. I once asked him for the recipe of Church on a Hill... he said they really push the yeast and add oxygen and nutrients more than once in the process.
I agree on the olive oil industry being largely corrupt, but I can tell you that the Costco brand is legitimate olive oil (reviews, etc) and also the best value in case you wanted to give it a go.

 

[cervid]

I didn't realize Cigar City was adding O2, I wonder what the schedule is? I thought for a while that oxygenation was overblown, especially in the long term, and especially if it's added near or at terminal gravity since the yeast don't have the food needed, the O2 just sits there, right?

After reading the one or two studies on Olive Oil I then again figured it was legit. I mean, why go through all the trouble to use Olive Oil, in their words, "to get a few more weeks shelf life" if oxygenation wasn't indeed a concern and/or noticeable by people with better palates than I.

This is one reason I had been looking into closed pressurized fermentations for a while. I thought a lot of (most) breweries did that to eliminate O2 and light exposure, and with this technique the Olive Oil thought makes sense. I mean, we all get preached to about making sure they start off on Maltose so they don't get lazy with simple sugars and then shocked going into maltose rich wort. Perhaps the same idea applies to wort. Start them off anaerobically and just give them what they would have gotten from during the aerobic process.

Your point about cigar city also makes me wonder. I've been planning on getting a big RiS in a fermenter soon and I wonder if doing a staggered nutrient addition like I've done with Mead would make sense. Maybe even be tighter with the schedule and get 100% of the nutrient and energizer into the fermenting beer before 1/3 of the sugars are consumed.. Or even all at once in the beginning like I used to do with Mead. I use the same stuff in my starters after all.. Maybe that's the ticket over to start.. Give them some DAP and energizer after 24-48 hours, after they have burned through the FAN and other nutrients inherent in wort, keep them anaerobic and just give them more nutes..

I'm just about to get a stir plate and start farming yeast off my starters to cut down on costs though, I think I need to really get that process down before trying Olive Oil, although it does make me wonder..

We don't have a Costco here, although we did out west. I just get Sam's brand since it's so cheap and we use a lot. I don't trust it either, but I don't care, it tastes good and I'm not buying the organic stuff.

 

[davidgsmit]

Well, Ive always wondered how much o2 gets introduced with a bottling wand. The beer shoots out petty quick at first and you do that over 50x per 5 gal of beer, but I've never gotten an oxidized bottle off of it, so it seems the yeast do indeed consume that o2 in priming the bottle.

Last night i drew off a half gallon of my RIS and shook it up real well and put it back in. It had been fermenting for 24 hrs at that time and was respectfully chugging along, but this morning when i looked at it it was getting violent, even though i dropped the ambient temp by four degrees (was finally able to pull my ipa out of the fermentation chamber and put the RIS in last night which was running 5 degrees too hot). So despite a four degree drop my blowoff tube is bubbling twice as fast now. Decided to drop it another degree this morning. Seems to me it had a significant impact.

I also sent an email to New Belgium; will keep you guys posted on what they say.

 

[aiptasia]

CCB isn't the only brewery doing the additional nutrients and O2 supplementation. Dogfish Head does this to produce beers like 120, WWS and Utopias. I wouldn't doubt it if Wayne was using supplemental oxygen additions in beers like Zhukov and Hunahpu.

I'm squarely in the camp of using O2 to feed the yeast in my worts. I broke down and bought the stainless steel O2 wand and basic regulator from NB and bought my O2 tank from Lowes for $10. I've done maybe 20 batches so far with it and it's been a fantastic addition to my brewing. Even on the biggest of worts, i've been able to break the 1.020 barrier repeatedly with adequate pitching and oxygenation. My worts get a full 1 minute blast of pure oxygen just after I pitch the yeast. I find the jacuzzi-like bubbling to be a great way to mix the yeast into the wort, too.

The reason I don't like olive oil additions is that for every beer i've tasted that were brewed using that method, I can taste the residual olive oil flavor in the beer. Don't get me wrong, I love olive oil and cook with it every day. However, I do find it to be an off-putting flavor in a beer, especially when i'm not expecting it.

 

[billl]

Honestly, I wouldn't worry too much about this unless you start to encounter some problems. There are really a lot of variables that we aren't controlling nearly as well as we sometimes think we are. eg if you are off 5% in your aeration level, your yeast are 5% more viable than some calculator projected, your home was a little warm when your made a starter etc and they all add up to 10% variation in some starting conditions..... after a couple generations of exponential growth, you could easily be +/-25% in your total yeast cell count. If you are in the plus direction, you may never even notice that your aerating practices weren't perfect. If your starting cell count was low, you might well blame aeration when it was actually the pitch causing the issue.

So, just give it your best shot and see how it turns out. If you run into issues, then start tweaking variables within your process to see how you can overcome those issues. People were making beer for hundreds of years before they even knew yeast or O2 existed.

 

[davidgsmit]

Glad to hear that's been working well for you. How many batches can you manage with a store bought tank? Sounds like a worthwhile way of going about it.

I'm thinking the batch(es) you've tried that had olive oil weren't done right. You can literally take a toothpick, dip it in the oil, then dip it in the wort. A fraction of a drop is all it needs over 5 or 6 gallons. I don't think you could pick up on that even on the lightest of beers.

 

[aiptasia]

Glad to hear that's been working well for you. How many batches can you manage with a store bought tank? Sounds like a worthwhile way of going about it.

I'm thinking the batch(es) you've tried that had olive oil weren't done right. You can literally take a toothpick, dip it in the oil, then dip it in the wort. A fraction of a drop is all it needs over 5 or 6 gallons. I don't think you could pick up on that even on the lightest of beers.

It does work pretty well for me. I can't really answer your question yet because in the last 20 or so batches, I have yet to run out of pure O2. I've had the oxygenation rig for almost two years now and it's still going strong on the first tank I bought. Again, the worts only get about a one minute shot of O2. Just be sure that if you get one, you clean and sanitize the airstone in hot water. You can do this by floating the airstone in your strike water as it heats up to temperature and then giving it a little ten second blast of oxygen to force any wort gunk out of the pores.

As to the olive oil, the only beers i've tasted that used the olive oil addition were commercial examples, and they used wayyyy more than a toothpick drop amount. I'd have to go back and browse through my untapp'd notes, but there are two or three of them that i've picked up the olive oil off flavor in the beer.

 

[davidgsmit]

So I picked up the aeration wand/system from Williams Brewing this week... sure has some great reviews and I've looked at it in the past, so I bit the bullet.

With regards to the olive oil; I got a response from Grady Hull at NB regarding their experimentation with it. He said:

"Yes, we did try using olive oil on a commercial scale as a yeast nutrient to replace oxygen but we went back to using air or oxygen for our normal production. The reason was that we didn't get enough of a shelflife improvement to justify installing an olive oil handling system. Also, we saw a slight increase in esters. I've attached my thesis on the subject, which can be handy if are having trouble falling asleep at night."

His thesis is actually readily available on the web and can be found here:
http://www.brewcrazy.com/hull-olive-oil-thesis.pdf

Sounds like they didn't see any significant downsides to the use of olive oil and their sensory panel actually preferred it by a very small margin, but again, they couldn't justify the cost of adding it into the system. It does mention that it takes longer for the beer to finish fermenting, which for a commercial brewery would be a real disadvantage. Next time I do another big beer and split the batch I think I'll try it again to see if it finishes out.

 

[EarlyAmateurZymurgist]

I also can't comment on the use of olive oil except I know that it has been done successfully.
In regards to oxygen for fermentation. Yeast would much rather undergo cellular respiration instead of fermentation. Cellular respiration(oxygen present) yields 28 ATP for every molecule of glucose which gives the cell enough energy to manufacture their cell membrane and sends acetyl co A in to sterol production mode. Sterols are needed for cell membrane integrity and health. When you pitch yeast in to oxygenated wort they will use up 100% of it in 30 minutes time.
Fermentation (without oxygen) yields 2 ATP for every glucose molecule so you can see why they would rather their be oxygen present. When the oxygen runs out acetyl co A gets put to use manufacturing esters so that is one way to control ester production. No oxygen = no cell growth. You need growth for flavor production and to build up enough healthy cells to finish the fermentation process. Some people add oxygen to the wort a second time about 12 to 18 hours after the initial oxygenation and yeast pitch but that is just for highly concentrated worts. They wait that amount of time to let the yeast go through at least one doubling then add more oxygen to give them a second round of growth. With everything you do there is some sort of effect so just keep that in mind. With a beer as big as what you are talking you really should use pure oxygen due to the low solubility of high gravity worts. Without buying an O2 setup I would say your best bet is to pitch another slurry of actively fermenting yeast if you think they are going to have a hard time reaching terminal gravity.

Hopefully that clears up some of the oxygen confusion. Someone correct me if I got something mixed up.

Actually, the Pasteur effect does not apply to brewing yeast strains that are pitched into normal brewing worts. All carbon source utilization is via the fermentative metabolic pathway from the moment that the culture is pitched due to the fact that the glucose level exceeds the Crabtree threshold. Any oxygen uptake that occurs while the glucose level exceeds the Crabtree threshold is shunted towards the production of sterols and unsaturated fatty acids (UFA) via the respirative metabolic pathway.

The reason why we aerate a culture is so that the mother cells can build up the sterol and UFA reserves necessary to complete fermentation. Sterols and UFAs make yeast cell membranes pliable. As all carbon source uptake and waste removal occurs via the cell wall, cell membrane health is critical to fermentation. The sterols and UFAs that were built up by the mother cells are shared with all of their daughter cells. If there is shortage of sterols and UFAs in the mother cells, fermentation will stop before the desired terminal gravity is reached due to the fact that the cells can no longer take in carbon and expel waste through their cell walls. The same kind of thing happens when the alcohol level exceeds a certain threshold. However, in that case, it is because the cells become dehydrated and can no longer move nutrients and waste through their cell walls.

Adding olive olive to wort allows the yeast cells to bypass the biosynthesis of sterols and UFAs; thereby, eliminating the need to oxygenate wort. Oxygenating wort has several downsides including chemical oxidation and the possibility of triggering diauxic shift at the end of fermentation. Diauxic shift is a phenomenon that occurs if there is oxygen available after all of the glucose and the sugars that the yeast cells can reduce to glucose have been metabolized. During diauxic shift, yeast cells switch into aerobic utilization of ethanol as their carbon source.

With that said, dry yeast manufacturers propagate yeast respiratively in a device known as bioreactor. The low-gravity highly-oxygenated culturing medium is held at a steady state below the Crabtree threshold by continuously adding new nutrient while removing yeast. This process results in explosive yeast growth because respirative growth is more efficient than fermentative growth.

 

[EarlyAmateurZymurgist]

I thought for a while that oxygenation was overblown, especially in the long term, and especially if it's added near or at terminal gravity since the yeast don't have the food needed, the O2 just sits there, right?

If dissolved oxygen is available after all of the glucose and all the sugars that can reduced to glucose have been consumed, the yeast will shift to consuming ethanol aerobically via a phenomenon known as diauxic shift. Diauxic shift is one of the reasons why breweries are looking for ways to avoid oxygenating wort.

 

[davidgsmit]

Good info. Correct me if I'm wrong but it sure sounds like one must try rather hard to over oxygenate a beer as long as A, the yeast are still active, and B, there's still fermentable sugars available to be digested. We're assuming an addition of O2 here after the fermentation has started, but only a short addition/burst.

With breweries trying to omit the use of O2, are you implying that there will always be a risidual effect from the use of O2? Seems like the primary intent of trying the olive oil for New Belgium was "shelf life". If the yeast eat it, why is it still a concern later on in other words?

Thanks all

 

[EarlyAmateurZymurgist]

With breweries trying to omit the use of O2, are you implying that there will always be a risidual effect from the use of O2? Seems like the primary intent of trying the olive oil for New Belgium was "shelf life". If the yeast eat it, why is it still a concern later on in other words?

Chemical oxidation is not restricted to hot wort. Cold-side aeration also shortens the half-life of the finished product. A high dissolved O2 level translates to a longer period in which oxygen is in contact with the wort.

 

[Seven]

If dissolved oxygen is available after all of the glucose and all the sugars that can reduced to glucose have been consumed, the yeast will shift to consuming ethanol aerobically via a phenomenon known as diauxic shift. Diauxic shift is one of the reasons why breweries are looking for ways to avoid oxygenating wort.

This is interesting but what do you think homebrewers should actually do when it comes to aerating their wort? I'm familiar with the New Belgium thesis but did any conclusive results come out that said homebrewers should now do X, Y, and Z when aerating? Should we aerate at all? And are average gravity beers (~1.060) treated the same way as high gravity (~1.085+) beers? Thanks.