Respiration vs Fermentation

[gravy]

Everyone knows that ethanol is produced by yeast during the anaerobic respiration of sugars. Everyone knows that anaerobic means without oxygen. Everyone just assumes that anaerobic respiration occurs because oxygen isn't available, but it isn't as simple as that:

Saccharomyces cerevisiae (brewers yeast) prefers fermentation to respiration even in the presence of oxygen and will yield ethanol even under aerobic conditions given the right sources of nutrition.

Do a Google search and see if I'm telling the truth.

Initially this seems a little odd, but when you think about it, it actually makes a lot of sense. Yeast developed the ability to produce alcohol for reasons that have nothing to do with the convenience of brewers. When yeast finds a food source it reproduces as fast as it can then starts to produce alcohol as fast as it can. Anyone who has tried to restart a stuck fermentation knows that when the alcohol gets above about 5% its near on impossible. The yeast creates an environment in which nothing else can get established and the production of alcohol is the key. When the sugar is gone, the yeast will consume the alcohol areobically - by doing it in that order it doesn't have to share. Consuming the sugar aerobically from the start would almost guarantee competition.

You don't evolve a high tolerance for alcohol and then not use it - what would be the point?

Learning this changed my attitude to the use of aeration. With high gravity fermentation the risk of spoilage organisms is low, but establishing a viable yeast colony is tough for the same reason. Yeast are better, stronger, faster with access to oxygen, but standard brewing practises make a big point of excluding it. Whenever you read anything about high gravity fermentation they always talk about the need for aeration, but I was always hesitant thinking aeration meant no alcohol.

Yeast will respire aerobically to assist with reproduction so more sugar will end up as yeast biomass. The trick is to supply enough dissolved oxygen to create a kickass yeast colony that will quickly ferment to dryness. Any more than that is wasted, but buying yeast will always be more expensive than growing it.

Aeration when sugar is getting short is a bad idea as it will lead to the consumption of alcohol, and that's my job and I don't want to share!

With my washes I currently push 70 litres/minute of aeration through a 200 litre wash for the first 12 hours. Its forced through an air curtain that runs around the fermentation vessel. Less like a fizzing airstone and more like a spa pool with the bubbles on. Don't be afraid to give it a try.

[rad14701]

Good write-up, gravy, but I'm not sure whether you were making a point or just making a statement... I've read a lot about yeast, what makes them happy, and how to propagate yeast strains, and I still feel like I know very little about yeast... Of course, that's what the yeast experts say, too... Just when you think you have one strain figured out, it throws you a curve ball...

You are correct in that yeast should only be aerated during the initial multiplication phase - at least for most yeast strains used in brewing... The added oxygen helps them breed... The lack of oxygen causes them to expend more energy converting sugars to ethanol... And then, at some point, all bets are off and the yeast strains characteristics dictate what happens next...

I never reuse my yeast and normally don't over-pitch either... I let the colony multiply and get happy before popping the airlock in place... From then on I do whatever it takes to not end up with vinegar instead of ethanol...

[punkin]

Seen ya say a lot of times that you leave the airlock out to allow your yeast access to oxygen and make them 'breed' up Rad.

How do ya reckon that works?

Cause just thinkin about it, with the yeast producing Co2 as a byproduct, and Co2 being heavier than air and all, and a fermenter being a well with a catchment that would not allow air currents to replenish a gas cap, and an airlock hole only being a small sorta vent an all........

Seems to me that all you are doing is allowing a gap that permits dirt, bugs or infections in but not doing one damn bit towards your stated purpose.

I'm sure if the Co2 didn't form a blanket then open fermentation wouldn't work as well as it does for an industry standard....


Interested in your thoughts.

[big worm]

unless you injected air or gave it a good stir the blanket afect co2 would bar oxy. from reaching the yeast i would think

[pHneutral]

Its terribly geeky to do this, but if you really want to make sure no O2 is in there at some point, sparge the thing with N2 (CO2 would be ok but you wouldn't want to do it too long unless you watched the pH. It's also not a neutral gas to the yeast, which N2 is) with the airlock on. Put in a few airstones, run N2 through them for an hour and that will get most of the O2 out of solution.

[rad14701]

Punkin, I think along the same lines as you and big worm regarding the CO2 layer blocking additional intake of O2... The development of a kraeusen would also serve as a block against further O2 intake...

I generally aerate, by stirring or shaking, two or three times during the time period before inserting the airlock... I don't have to worry about nasties getting into the mix, and if I did I'd probably cover with a towel... I've even used the airlock and then opened the fermenter up for aerations... I'm essentially using the wash itself as a yeast starter without the benefit of proofing...

It's also worth noting that, according to most yeast information, yeast double in numbers every three hours, and I only allow them one hour, the additional one third in yeast volume may not be worth the added effort...

[punkin]

So the stirring is doing the aeration? You have to take the lid off to do the stirring (or the shaking otherwise it comes out the hole) so what purpose does leaving the airlock out serve? And are you saying you leave the airlock out only for an hour?

Not trying to harangue you, just trying to understand why you are promoting this practise.








JustGotMeStumpedPunkin

[rad14701]

So the stirring is doing the aeration? You have to take the lid off to do the stirring (or the shaking otherwise it comes out the hole) so what purpose does leaving the airlock out serve? And are you saying you leave the airlock out only for an hour?

Not trying to harangue you, just trying to understand why you are promoting this practice.

Not a problem, punkin... I've been adjusting my method over the last couple months which is why I sometimes use the airlock and sometimes don't...

Here's what I've garnered from much reading about yeast... With the presence of O2 yeast will simply multiply, releasing little CO2... The lessening of O2 will cause the yeast to slow multiplication and will increase the manufacture of CO2 and alcohol...

Therefore, it really wouldn't matter whether the airlock is in place or not, until the O2 levels in the wash and in the air space within the fermenter is becoming depleted... Airlock or no airlock really isn't coming into play as long as the wash itself still has enough O2 to prolong propagation of additional yeast rather than conversion to alcohol... Constant aeration, using an air stone and pump might enhance the process by putting additional O2 into the wash, and perhaps forcing some of the CO2 off the surface of the wash and forcing air flow through any developing kraeusen on top of the wash... This is why stirring initial kraeusen down into the wash is recommended in some circles...

If anyone has additional input on this I'm all eyes and ears... I'm not a yeast expert by any means, merely sharing my personal views based on what I've read and tried... My apologies to gravy if we've hijacked the topic... Not sure if this discussion would be better served in a new topic or not...

[brewmaker1]

I seem to remember some of the same things as Rad says about yeast multiplying more than creating Co2 in the presence of o2, but I'm changing my way of thinking about the o2 in the atmosphere vs. o2 in the wash/wort. Reading this: http://www.maltosefalcons.com/tech/MB_R ... turing.php" onclick="window.open(this.href);return false;" rel="nofollow I'm starting to think it doesn't matter so much whether the fermentor is open or closed (airlock). What matters is the aeration of the wash/wort in the beginning hours. It needs a buttload of oxygen in the wort.

The web page I linked to is talking about yeast for brewing, but the same principle would be applied to distilling. Fermenting is fermenting

[zymos]

Blanketing by CO2 aside, I think there is a pretty big difference between actually aerating a volume of liquid and merely exposing its surface to air...

[brewmaker1]

I agree. The liquid should be agitated (stirred) a few times in the first few hours. That would help put the o2 in the solution.

If anyone is interested in building a stir plate for making starters. A small computer fan works very well and should cost less the $10. A small metal rod about an inch long gets placed inside the vessel for the actual stirring.

[rad14701]

That's my line of thinking, too, brewmaker1... The yeast aren't going to swim to the surface for air, it needs to be introduced into the slurry where they reside... The only real difference the airlock makes is the amount of vessel pressure created and whether that has any effect is debatable... The airlock also keeps the nasties out...

[gravy]

Thanks for the responses. My main interest is in the fermenation to dryness of high gravity washes with a result above 18% alcohol. I tend to make the mistake of assuming we are all trying to do the same thing, but we're not.

In addition to my original post:

Anyone wanting to find out more about aerobic fermentation should look up the Crabtree Effect. He discovered it (but yeast already knew about it).

Simply exposing a brewing container to the air doesn't do much to increase dissolved oxygen. Ask a goldfish. Getting oxygen dissolved in a wash is even more difficult due to tthe increased temperature and quantity of dissolved sugar. With air as the oxygen source reaching 8ppm is very difficult.

Acetic acid is produced by a bacterial infection. Aeration itself won't cause this, and since it is also the result of an anaerobic process aeration doesn't assist it. Aeration, however, is a means for the bacteria to be introduced, but I've never had it happen.

OK, the question is who can provide me their fermentation results? Preferably sugar washes. I'd like to know the quantity of sugar used, non fermentable soluble solids (if applicable), OG, FG and the yield they get after distillation. I would really appreciate it.

Please include heads and tails quantities, and an SG of the wash after distillation (and cooling) would earn you extra points.

[gravy]

Brewmaker1 - that is an interesting link.

I think the point is that anything was better than the airlock, but the comparison between shaking, stirring and aeration isn't entirely balanced since the shaking and aerating were done 3 - 6 times a day but the stirring was continuous. Beyond the aerating effect of stirring there is clearly a benefit in plain old agitation. It has to assist the yeast find the nutrients and keep everything in suspension. The trade off is loss of yeast due to shear stress. In any case, I also have a liquid pump circulating my wash at around 20 litres per minute so I am a convert. I couldn't find a stirrer device on the scale required that was weatherproof enough to live outside.

Fermenting is fermenting, but fermenting from a starting gravity of 1.040 isn't the same as from 1.110. Its much harder to get oxygen dissolved and the yeast has got much more work to do in a much tougher environment. Also the Crabtree effect refers to the behaviour of yeast exposed to high glucose concentrations - I'm not sure 1.040 counts as high.

[brewmaker1]

Agreed, starting with such a high gravity will shock just about anything. I did a quick search and found white labs has a new strain for high gravities but it has to be built up in steps. Here's the link http://www.whitelabs.com/gravity.html" onclick="window.open(this.href);return false;" rel="nofollow I can't help any with sugar washes because I haven't tried one yet. I'm still having too much fun with all-grains. As for yeasts, my experience has only been ale yeasts. Maybe others can chime in for the other type yeasts.

I'm also using a pump with my fermenter, but not for stirring. I use a fairly high velocity pump from my mashtun to fermenter and have a flat nossle on the hose so it sprays the wort into the fermenter. It causes some serious aeration. From what I'm reading though, I need to make a bigger yeast starter. That one link I posted earlier explains why some of my beer has off flavors after aging. It's not really a problem with distilling, but it sure wouldn't hurt to do it right all the time.

[punkin]

Simply exposing a brewing container to the air doesn't do much to increase dissolved oxygen. Ask a goldfish.

Exactly.

specially when the oxygen can't even get into the container.....

[muckanic]

Without claiming any sort of authority here, there are a couple of widespread ideas in this area that I would question:

1. CO2 acts as a blanket against O2. My understanding is that what makes O2 flow (into a fermenter) is the O2 pressure gradient, not the total gas pressure gradient. IOW, CO2 can't substitute for O2.

2. Yeast crack sugar in order to get at the O2. I always thought they were simply after a carbohydrate energy source, like many other living things.

[zymos]

1. is the law of partial pressures, IIRC, and you are correct. Except a blanket a CO2 does "protect" the volume of liquid from O2, not because of any pressure it is exerting, but simply because it is a layer that the O2 must pass through before it can reach the liquid...
At least that's my understanding.

[LWTCS]

Hopefully this is relatively on topic.
I started an apple sause wash today. A total of maybe 10 liters. I aerated the wash profusely with a large wisk while waiting for the temp to fall to my pitch range. Then I pitched my yeast and wisked three more times within maybe 15 minutes. After each time I wisked, a nice batch of foam became more prominent on the surface. For some reason as i was admiring the the foam kind of caking up, I knocked (with my knuckles) against the sides of my plastic fermentor on either side. I noticed an immediate sort of foamy flare up where I was knocking. I started knockng around the perimiter of the fermentor and where ever the vibration was the foaming would accur.

The kinky part:
I pluged in my wife's,,,,,,,,,,,,back messager vibrating device, and turned it on high and placed it on the outside of the (25 L plastic ) fermentor wall. While turning/slowly spinning the fermentor I vibrated the wash for maybe 5 minutes. Holy genisis bat man, what a reaction I got from that. The cake just multiplied by 5 or 6 times or so.

Has anyone else vibrated their washes?

[Dnderhead]

Id have to say you dislodged the co2 that was in the wash . not creating more.

[LWTCS]

Beneficial or detrimental?

[Dnderhead]

neither . just like bumping a beer. take a beer/soda and use that thing on and see what happens

[pro65]

OK I am lost with all of this chemist talk. So here are some questions yes or no.
1.After all the ingredients are in the fermenter you need to get allot of air worked into the mash.
2.use an air lock on fermenter?
3. Would it help the wash if it was constantly stirred through out the whole fermentation cycle? ( using an ice cream churn motor and a drill type paint stirrer).

OK I understand that the yeast is mixed all through the mash and after the mash sets the only air it has is on the very top and the yeast down in the fermenter has no air. Am I correct so far?

When the yeast is splitting or whatever it does that is when it is eating up the sugar from a bag or what ever it is from the grain bill (no bag sugar) and at this point ALC. in being made?

Now when I make a batch of all grain I stir it allot and then add my air lock, the next day I pull the lid and stir it again and replace the lid, and so forth until the bubbling is either very slow or non present through the air lock.

I know this can lead to contamination but I TRY to be very careful so should I do it like this or not?

Last but not least if air is not good for a wash how was it done in the old days, they just covered it with cheese cloth or left it completely open.

[Dnderhead]

I'm a simple guy so one at a time yeast needs oxygen to multiply . that is why you should aerate at the beginning.
after there is enough yeast and then you want no oxygen and the yeast gits its energy from the sugar that makes alcohol.as a byproduct
air locks/covers keep out unwanted yeast/molds etc that will infect wash.
some of the "big boys" stir constantly but not necessary with small sized wash Theo it mite help? (keeps yeast in suspension)
opening the fermenter leads to chance of contamination best to do with out opening the fermenter.

[Dnderhead]

iv seen wood water vats/tanks used for fermenters, just lade boards on top for a cover. but there were also bugs, squirrels, rats etc in there also
efficient? not likely, air on top is not the problem it is in the wash that affects it (thank stale water)
and if air currents do not disturb it there will be a blanket of co2 on top.that keeps oxygen away.