Fermenter Airlock Pressure

[robheffo]

Hello,

As a I have been trawling all over the interwebs trying to find an answer to what I thought would be an easy enough question.

I was wondering how much pressure builds up inside the fermenter before the airlock releases a bubble of gas?

I need to know as I am wanting to build a setup that uses a pressure sensor to detect the bubbling rate, and there are a LOT of different types of sensor and I want to get one that is suited to the task.

Regards,
Robert Heffernan,
Albury, NSW

 

[zabond]

As gravity is 14psi pushing down on the air lock fluid I would think the ferm pressure would have to build up to above 14psi for it to force a bubble of co2 out, so a sensor range of 12-16 psi

 

[Supra-Jim]

I think the pressure build up is fairly low. It's easy to work out as the pressure difference between the inside of the fermenter and the ambient pressure will simpy be a function of water level in your air lock (assuming you use one of those s-bend style ones).

EG. a 10mm difference in height equates to 1mbar (assuming you have water in your airlock). Hence the pressure difference is very low. (10m of water = 1bar = 1000mbar)

So simply work out how high the gas pressure needs to raise the water in the airlock, measure this, then simply perform a pressure conversion calc.

Cheers SJ

 

[QldKev]

Hello,

As a I have been trawling all over the interwebs trying to find an answer to what I thought would be an easy enough question.

I was wondering how much pressure builds up inside the fermenter before the airlock releases a bubble of gas?

I need to know as I am wanting to build a setup that uses a pressure sensor to detect the bubbling rate, and there are a LOT of different types of sensor and I want to get one that is suited to the task.

Regards,
Robert Heffernan,
Albury, NSW

I'm not sure on the pressure to bubble through an air lock. It would be easy enough to hook up a compressor to the bottom of an air lock and slowly increase the pressure until it breaks through; it will not take much pressure at all. I think it will also vary with the amount of water in the airlock, and the airlock design.

The air lock is just a basic way of preventing air / wild yeast entering the fermenting chamber. In brewing I believe you would be better of reducing as much pressure from the fermenting chamber as possible. This would minimise the CO2 absorbsion of the wort allowing a fuller / cleaner ferment. Some better brews are open air fermented; often in a room with filtered air.

So for this project if you really want to measure the amount of CO2 lost through fermenting, I would use a simple 1 way valve, with a gaseous flow meter attached.

QldKev

 

[RdeVjun]

Supra-Jim is quite right, the pressure is equivalent to only a few cm of water, so 2/3 of bugger all. Unlikely that it will be cost- effective to buy a pressure sensor which can detect it.

If bubbling rate is needed, then why not measure it directly with an NCBE Bubble counter?

 

[Supra-Jim]

Also, Heffo, can you give us some further info as to what your planning and why?

The reason i ask is if your planning an elaborate method for measureing bubble rate to use as an indication of fermentation progress, i suggest you have a look at some of the previous threads about air locks not bubbling!

Remember too that yeast can function under much higher pressures than that in fermentation, as evidenced by the time honoured practise of bottle conditioning/natural carbonation. However not sure however if a significantly higher pressure during fermentation would affect the yeast.

Cheers SJ

 

[alowen474]

I would imagine it would have to do with the height of water (head) and the area acting on the water.
As gravity acts at 9.8m/s/s, and the water would need to lift say 2cm, height of water would be 0.02m.
If I can remember my fluid mechanics, this would result in a force of .196n.
Over the area of say 1cm2 in the airlock we would need .3psi.
Very vague recollections here.
Anyone help me out?

 

[Supra-Jim]

off the top of my head, beerforall, i don't think surface area comes into play, because the surface area on either side of the liquid is the same (hence you can cancel it of each side of the equation).

the height of the liquid in mmWC (millimeters Water column) can be measured and converted to whatever unit you like.

Cheers SJ

 

[jonocarroll]

This is the calculation as I see it... http://www.aussiehomebrewer.com/forum//ind...st&p=405821

As gravity is 14psi pushing down on the air lock fluid ...

:blink: Gravity is a pressure now?

As SJ said, surface area is irrelevant.

I'm still yet to hear a genuine reason why the miniscule pressure that an airlock provides is detrimental to the yeast activity. That, however, is completely different to the argument that the layer of CO₂ above the beer is detrimental, and that an open-ferment has advantages; the partial pressure of CO₂ in the atmosphere above the liquid will affect the equilibrium of dissolved CO₂.

 

[Dazza_devil]

After returning home this morning I can tell you that enough pressure can build up in a 2 piece air lock to blow the lid off and spit krausen all over the roof of your brewing fridge. The cap on it must of been stuck on a little. I've cleaned it up and set up a blow-off tube but it didn't look good, CO2 blowing out a hole in the krausen that filled the airlock. Fingers crossed nothing got in. I wont be using airlocks after this, just set up a blow off tube and be done with it.

 

[Adamt]

I'm still yet to hear a genuine reason why the miniscule pressure that an airlock provides is detrimental to the yeast activity.

You won't.

After returning home this morning I can tell you that enough pressure can build up in a 2 piece air lock to blow the lid off and spit krausen all over the roof of your brewing fridge. The cap on it must of been stuck on a little. I've cleaned it up and set up a blow-off tube but it didn't look good, CO2 blowing out a hole in the krausen that filled the airlock. Fingers crossed nothing got in. I wont be using airlocks after this, just set up a blow off tube and be done with it.

That's because it got some krausen or something stuck in it.

 

[robheffo]

Thanks for the response guys, It has been EXTREMELY helpful.

From what I have been able to work out from the responses to my question, the differential pressure between the fermenter and outside world is rather small. I will then look at a 0.1mbar pressure sensor (about US$65 from digikey)

I am planning to build a storage cupboard to hold a pair of 25lt brew buckets and an electronics system to monitor, log and even control (as much as one can) the fermentation process. I am (unfortunately for my bank balance) one of those people who subscribe to the notion of "If something is worth doing, it's worth overdoing!"

To detect the bubbling rate, I will watch the pressure inside the fermenter, and when there is a decrease in pressure then I will assume that there was a release of a bubble. From there I can work out the rate of bubbles per minute, as a loose indicator of the rate of fermentation.

 

[Dazza_devil]

Thanks for the response guys, It has been EXTREMELY helpful.

From what I have been able to work out from the responses to my question, the differential pressure between the fermenter and outside world is rather small. I will then look at a 0.1mbar pressure sensor (about US$65 from digikey)

I am planning to build a storage cupboard to hold a pair of 25lt brew buckets and an electronics system to monitor, log and even control (as much as one can) the fermentation process. I am (unfortunately for my bank balance) one of those people who subscribe to the notion of "If something is worth doing, it's worth overdoing!"

To detect the bubbling rate, I will watch the pressure inside the fermenter, and when there is a decrease in pressure then I will assume that there was a release of a bubble. From there I can work out the rate of bubbles per minute, as a loose indicator of the rate of fermentation.

I've missed the point of your whole exercise somewhere, is it going to improve your beer and how?
I would say that there are too many other independant variables to gain anything from the exercise.
In my opinion there are many other more important factors to gain control of other than the airlock bubble and such an exercise would prove to be futile.

 

[robheffo]

It's going to improve my brew by mainly being able to monitor and regulate the temperature (both heating and cooling) of my brew since my house being largely uninsulated (old, weatherboard with temperature swings of up to 30 degrees and beyond) is a pain to moderate the temperature so being able to regulate the temperature in a closed environment will help heaps.

Adding the extra information gathering (like bubble rate) to the temperature control electronics is rather simple and since I can do it, I might as well. I was after the pressure information so I could size up the correct sensor since there are a million types with different pressure ranges and vastly different price points (US$22 to over US$160)

The rest of the information is largely for my own personal consumption.

 

[Dazza_devil]

I can see your angle here mate but simply opening up the door of your regulated temperature controlled area will stuff your results. Your enclosure may also need to be completely airtight. I reckon heating and cooling of the surrounding air will also impact the bubble rate. You may need many sensors in many different areas. The variables are too numerous for me to contemplate.
The yeasty is a living organism and I think there will be many other factors controlling it's CO2 production other than temperature. I'm also of the opinion that CO2 production may be a minor discerning factor in the quality of your brew and yeast health.

 

[hoohaaman]

After returning home this morning I can tell you that enough pressure can build up in a 2 piece air lock to blow the lid off and spit krausen all over the roof of your brewing fridge. The cap on it must of been stuck on a little. I've cleaned it up and set up a blow-off tube but it didn't look good, CO2 blowing out a hole in the krausen that filled the airlock. Fingers crossed nothing got in. I wont be using airlocks after this, just set up a blow off tube and be done with it.

3068 ?

 

[Dazza_devil]

3068 ?

3638

 

[hoohaaman]

well I like both

 

[seemax]

You want to spend US$65 on a pressure sensor when you can get a fridgemate for $40 that will regulate your fermentation temperature within 1C ? *confused*

Of course if you just feel the need to measure things and keep data to generate loads of graphs and animated power point slides... then that's also perfectly fine

 

[robheffo]

I can see your angle here mate but simply opening up the door of your regulated temperature controlled area will stuff your results. Your enclosure may also need to be completely airtight. I reckon heating and cooling of the surrounding air will also impact the bubble rate. You may need many sensors in many different areas. The variables are too numerous for me to contemplate.

My plan is to build the enclosure so that I won't really need to open it up unless deemed necessary, I will also be putting a viewport in the doors so I can observe the progress without needing to open the door.

You want to spend US$65 on a pressure sensor when you can get a fridgemate for $40 that will regulate your fermentation temperature within 1C ? *confused*

Yeah, I do , The whole project is going to be a marriage of my various different hobbies (woodwork, electronics, computers & beer) and where is the fun in buying something off the shelf when I got most of the parts floating around the house as it is, and I get the personal satisfaction of knowing it's all my own work.