What should I need and what should I want

What I've been getting at is having too much head space can give infection a chance to set in before the yeast can take over & produce enough co2 to fill the head space.

 

You want extra space in the fermenter to contain the krausen that occurs during peak fermentation. You should not need to worry too much about having too much headspace, Some brewers brew without a lid and that is as much headspace as you can get.

 

I concur. Don't worry about headspace too much. Just make sure it is sealed.

 

try doing 3 gallons in a 6.5 gallon bucket & tell me you're not worried about head space. Fermentation in those instances don't make enough co2 to protect the beer very quickly.

 

I brew 3 gallons in 6.5 gallon buckets every time i brew. No infection yet. How is the head space a concern in a sealed vessel? How does 3 gallons not ferment quickly enough to create CO2 off gas, but 5 gallons does???

Whether its 3 gallons or 5 gallons, they should theoretically produce CO2 at the same rate, providing off gas which in return will protect the beer underneath that layer of C02.

 

as and FYI on headspace, the approximate volume of CO2 produced is 60 gallons(air volume) per gallon of wort at a typical (1.040) gravity. So 3 gallons would produce 180 gallons of atmospheric CO2. So in a 5 gallon bucket, the 2 gallons of head space is negligable. If it is wort. If the contents are racked beer, then a CO2 purge would be needed.

 

I've done 2.5 gallon batches in a 6.5 gallon bucket and never once had an issue with oxidation or infection. The fermentation produces plenty of CO2... and with good sanitation, there's no concern.

 

While you might be producing co2 at the same rate,you won't be producing as much,due to the lower volume. Also,the co2 absorbes the o2,not mearly chasing it out the airlock. So the air in the head space must be absorbed by the co2 to protect the beer. Nasties generally need air to propogate. The sooner o2 is absorbed by the co2,the better.

 

I will have co2 on hand for purging and maybe for bottles by the time I make beer. It's heavier than air so it should be a layer over the yeast as soon as fermentation starts. Or I could purge the fermenter before I add the wort. Would I have to aerate for the yeast if I have a decent starter already whirlpooled?

 

That's the phalicy of common thinking. The gasses don't layer,they mix till the heavier gas absorbes the lighter one.

 

You should definately aerate. Remember oxygen is a good thing at the start of fermentation, so purging with CO2 into a primary fermeneter is kind of opposite of what you want IMO. You really can't oxidize a beer before it has fermented

 

So I should aerate the liquid, then if I want to purge I can purge the airspace and install my airlock, cause the air space doesn't help the yeast at all, only aeration does?

 

In my thought process, yes, this is perfectly fine.

Aerate wort, purge with CO2, put on lid.

 

Um... with all due respect, what on Earth are you talking about?

CO2 absorbs O2? Huh?

I must have slept through quite a few chemistry classes, because in all my years of science education, that's the first time I've ever heard that phrase... something is being lost in translation here...

 

Edit: because I don't have time to get in to a debate on the movement dynamics of a contained mixed gas system.

 

Nope. one of your bretheren on here that does research or something gave a long explaination on that one some time ago. Makes sense,as so many things in nature mix somehow rather than just layering. Our atmosphere is a perfect example. so if you've never heard of it,you weren't paying close attention. I got "A"'s in the living sciences. but they know even more nitty gritty details nowadays. So I remember some of this stuff.

 

Regardless of the settling issue... I still have no idea what you mean by heavier gasses absorbing lighter ones... do you mean that they simply mix?

 

I forget what the rate of absorption is,but yeah. As the co2 is produced & off-gassed,it absorbes the o2 trapped in the head space. When the gass reaches the right pressure,you see bubbles in the airlock.

 

If proper sanatation is used, why would this matter with 1 gallon or 5 gallons of head space? I mean if you've reduced the bacteria count to 1000, and are putting in 100 million (or billions) or yeast, how is the bacteria going to 'infect' it? And I admit that we reduce (sanatize) not eliminate (sterlize) our surfaces

And here we are probably talking past one another.

1. yeah as the CO2 is produced it will mix with the Air (N2/O2 mix) in the head space, as a whole over the ferment - usually at 90% at 2 days it will become the dominate, although not sole gas in the head space. For a period, there will be O2 in the headspace.

2. But there is also O2 in a properly aerated beer, typically a good shake/whip/stir will get about 4 to 5 PPM (Yeast by White) Ideally a target of 8 to 12 PPM is optimal (Yeast by White and How to Brew by Palmer)

3. And now some math. A quick interent search shows that at STP (32F) air needs 22.4l for 1 mole* of gases At 70F, it is 24l for 1 mole - ie more space needed.
Water has 55 moles per liter - I know wort is more than water, but for sake of simplicity....
Let me normalize that. 55.5 moles/L water and .042 moles/L for air. ~20% is O2, so only .0083 moles/L
Right, but we work in gallons and need to convert that. so in a 5 gallon batch of beer, 19*55.5=1054.5 moles/batch with 1.5g headspace, 1.5*3.7*.0083=.046 moles/headspace.

so 1054.5 vers .046 let's get this back to ppm. if we mulitiply each by 1000, we have 1,054,500 moles of liquid and 46 moles of O2.
This means we have about 46 ppm (above we wanted 8ppm to 12 ppm disolved). Not all of this can or will go into solution but thermo was never a strong point, and I don't think that this was a thermo or P Chem problem I've seen. I'd guess that atleast 1/2 and probably more than 1/2 of the air (N2 O2 mix) is displaced by the generation of CO2. There is mixing, but it all has to out gas somehow.

If we rescale this for our 5 gallon bucket, 3 gallons of beer and 2 gallons of headspace, the numbers looks something like this 632,400 v 61 moles - or about 96 ppm of the O2 in the head space of all the molecules in the bucket.

The 'magic CO2 blanket' in fermenting isn't magic, or a blanket, but nor is it so pourous that all the O2 in an early ferment is going to wreck wort or must.

I'd be currious to see if there are any studies of the transmission on a surface of a liquid of atmospheric gases into solution.

* what is a mole? A mole in chemistry is defined as enough molecules for a given molecule to have it's molecular weight expressed in grams, specifically this is normalized to a mole carbon 12 being 12 grams. But it is a way of counting the molecules in a given mass.

 

We also have to remember that o2 is driven out of wort during the boil. This of course is why we have to aerate it. so it re-absorbes some o2 from our actions. but I don't think it absorbes what it had before boiling. Unless you use an o2 cylinder & a SS airstone.
I tend to think the o2 from aerrating stays absorbed,due to replacing some of what was driven off. Although the rapid off gassing of co2 during initial fermentation likely effects this. but now we'd be talking about how fast the yeast cells absorb this o2 vs how fast it can be partially driven off by off gassing co2 during the reproductive phase,going into intial fermentation.
It also depends on other factors in one's process as to how fast all this happens. So it is conceveable that since we're sanitizing,& not sterilizing,that something could use the air to it's own dubious advantage. it does come up on here now & then. It would be interesting to see how fast surface transmmission works.
And then of course,we have oenning the fermenter for SG readings,etc. This I think starts the process over again,but to a smaller extent. Depending of course on how much one openns the fermenter as it gets closer to FG. This is how **** happens...

 

wow, a disaster of a thread. lol.

 

Well effectively the boil is going to drive off all the O2, randomness says it should leave some, but not much. I'd guess our tap water has no more than about 4ppm.
A quick look at some sources having to do with landscaped water features has the pre dawn O2 levels at about 4ppm -plants having consumed the free O2 during the night. It is interesting becuase this is what we can stir into things, which indicates that is the 'saturation level' that can be obtained from forcing O2 in at the surface, but again, I'd like to see some numbers. (at some point for every bit of O2 you stir/shake in, you sitr/shake it out)

The yeast use the O2 for making more yeast (sterol production for cells) and for general energy usage - ie making Sugar into CO2 and H20. And everytime we open up we put some more O2 back into the fermentor, and possibly a lot, if we give a good accidental mix of the air and head space.

Personally I don't worry about this, it sits for 3 weeks, and then goes to bottle, so there is little time for new O2 to get introduced. I don't bother with they hydrometer on most recipies anymore.

 

I do 10 gallon batches in a conical fermenter that is rated at 15 gallons, but actually holds around 18. That's my basis for headspace doesn't matter as long as the air isn't swirling above the wort introducing o2 directly to it.

 

i know. Try to read it through. I wish people didn't jump into a thread and start saying,

These guys didn't contribute. Thanks to all for cool responses and even the critic of my experiment that actually taste like biscuits with honey and jelly on them. It stinks though.

I'm going to use this bucket and get an airlock. Then I'm only going to purge if the beer I make tastes funny and I suspect it was o2, when I remake I'll purge the fermenter.

Apparently I can make as much or as little as I want in the bucket, as long as it isn't less than an inch from the top.

 

Oh... I see what you're trying to say. I was confused because the word "absorbed" isn't used for the process you're describing.

What you mean to say is something like this, "As the CO2 is produced, it mixes with the O2 already in the headspace. Both O2 and CO2, being gasses, exert a pressure on the container they are in. According to Dalton's Law of Partial Pressures, the total pressure of the resulting mixed gas is equal to the sum of the partial pressures of O2 + CO2. Thus as the pressure of CO2 rises, the total pressure in the headspace rises. Once the total pressure exceeds the downward atmospheric pressure on the airlock, you see bubbles."

But I'm sure that's what you meant, given that you got "A's" in science and all...

 

Yup. But by the time I got to collegein the early 80's,commII taught us to write the way we speak. IE,less formal,flowery language. It will then be easier to assimulate by the average reader. no need for science speak,in other words...To the others,it reads like we have an accord...

 

I have to laugh at this... you wouldn't understand why, but it's funny to me... One of the more interesting aspects of dealing with forums on the Internet is that you often have no idea who you are dealing with, or what their qualifications and skills are.

With that said, I'm going to go giggle to myself over a beer. Have a great night my friend.

 

I do not see how CO2 absorbs O2. CO2 and O2 are unreactive and will not combine into CO4 or any such like that. Sure, in a large enough container CO2 and O2 may stratify some but you would have a level between where there is a mix of the two gasses which in the small amount of headspace in a fermenter will pretty much be the whole headspace of the fermenter.

Warning. Math below.

During peak fermentation the CO2/O2 mix would be under enough pressure that the O2 would be diluted to near insignifigant levels by the sheer amount of CO2 produced by the frmenting wort. See the first post in this thread. Using the example from that post (113.8 Liters of CO2 per gallon of wort from a 1.055 OG wort with 75% attenuation), if there are even 2 gallons of wort in a 6.5 gallon bucket, the 227.6 Liters of CO2 should be more than enough to dilute and push the remaining O2 from the fermenter to negligible levels. Especially since the vast majority of fermentation activity happens within the first 2-3 days after the yeast gets to work.

</Math>

 

Hey,I didn't come up with the science,it's just how this friggin argument went when the shoe was on my foot. Now it's the other way around & people are changing there minds & ranking me. I'm not the "troll" here. It is what it is. Math is like surveys,they can be used to prove anything. Practice can be quite different. The math can't be counted on to be 100% correct 100% of the time. Deal with it.

 

I am not calling you a troll Union. I am just stating things as I see them, and what my experiences have yielded. The math was just to back up my opinions. That is the beauty of the internet and this forum. It is a place to share what you know/suspect and learn from it.