Unitank and spunding

[Bassman2003]

Thank you Doug. Gases are quite interesting and I clearly have a lot to learn.

It seems the "carbonation charts" are missing a data point. Without knowing headspace volume, there is not way to accurately asses end CO2 volume in the beer. I think we need a new carbonation chart which has an input column for headspace volume.

From my over simplified view, it appears the amount of CO2 in a vessel determines the amount of absorbed CO2 in the beer and any given temp/pressure. Meaning larger vessels just hold more CO2 which in turn gets placed in the beer even though pressure and temperature remain constant.

Makes logical sense as if one had a fermenter with almost no headspace, theoretically spunding would let most of the CO2 leave the container as there is nowhere for it to go beyond the given pressure. So "headspace" is kind of like a "holding space" for CO2 that might get absorbed if pressure or temps change.

 

[doug293cz]

Thank you Doug. Gases are quite interesting and I clearly have a lot to learn.

It seems the "carbonation charts" are missing a data point. Without knowing headspace volume, there is not way to accurately asses end CO2 volume in the beer. I think we need a new carbonation chart which has an input column for headspace volume.

From my over simplified view, it appears the amount of CO2 in a vessel determines the amount of absorbed CO2 in the beer and any given temp/pressure. Meaning larger vessels just hold more CO2 which in turn gets placed in the beer even though pressure and temperature remain constant.

Makes logical sense as if one had a fermenter with almost no headspace, theoretically spunding would let most of the CO2 leave the container as there is nowhere for it to go beyond the given pressure. So "headspace" is kind of like a "holding space" for CO2 that might get absorbed if pressure or temps change.

The headspace only makes a difference if you are not hooked up to a regulated source of CO2. If you cold crash a spunded fermenter, with no provision for adding more CO2, then the pressure is not constant. Cold beer can hold more CO2 than warm beer at the same CO2 partial pressure, so if you cool down a sealed vessel, the beer will absorb some of the CO2 from the headspace, thus lowering the pressure in the headspace. There is also a pressure drop just due to cooling the gases in the headspace. The spreadsheet I posted above does the calculation (a mass balance) to determine how much CO2 gets absorbed, and what the resulting headspace partial pressure of CO2 will be, for a specific set of conditions.

The existing carbonation charts are fine for what they are intended for, which is the case of constant CO2 partial pressure, controlled by a regulator. A chart for a sealed cold crash situation would need to be four dimensional, as the variables are starting pressure, starting temperature, ending temperature, and headspace volume to beer volume ratio. The spreadsheet takes all four variables into account.

Brew on

 

[DuncB]

With a slow cool, you will get some CO2 absorption during the cooling, so that when the beer reaches it's final temp, the headspace pressure will be lower than the "instantaneously" cooled pressure (I'd be interested to know by how much, and how long the cooling took.) It will also take a week or two to reach the equilibrium pressure at the cooler temp (just like set and forget forced carbing.)

Brew on

So 36 litre fermenter, with 18.5 litres of belgian tripel, headspace 17.5 litres, was 13psi at stable ferment and 22C.

So a week falling to ambient 12C and then been cold crashed at 2.5 C for 20 days.

Gauge pressure now reads 10 psi.

This doesn't agree with the cold crash calculator spreadsheet. No change of gravity so not a case of more CO2 being made.

So do I have youc calculator values of 1.92 vols or do I have vols of the carbonation calculator tables ( electronic version) which would suggest for 10psi gauge at 2.5 celsius of 2.45 vols?

I'm wanting to pressure transfer and then add sugar to get to around 3.3 vols using your other clever calculator.
I'm wondering if I aim for adding sugar to boost vols of CO2 to 3.3 from 2.45 ( ie an increase of 0.85 vols).
Depending on the actual CO2 vols based on your calculator giving the figure of 1.92 then at least I'll be at 2.7 vols which is well within the ballpark.

My suspicion is that my CO2 vols are actually going to be nearer the 2.45 vols when I start this process.

Any ideas?

 

[doug293cz]

So 36 litre fermenter, with 18.5 litres of belgian tripel, headspace 17.5 litres, was 13psi at stable ferment and 22C.

So a week falling to ambient 12C and then been cold crashed at 2.5 C for 20 days.

Gauge pressure now reads 10 psi.

This doesn't agree with the cold crash calculator spreadsheet. No change of gravity so not a case of more CO2 being made.

So do I have youc calculator values of 1.92 vols or do I have vols of the carbonation calculator tables ( electronic version) which would suggest for 10psi gauge at 2.5 celsius of 2.45 vols?

I'm wanting to pressure transfer and then add sugar to get to around 3.3 vols using your other clever calculator.
I'm wondering if I aim for adding sugar to boost vols of CO2 to 3.3 from 2.45 ( ie an increase of 0.85 vols).
Depending on the actual CO2 vols based on your calculator giving the figure of 1.92 then at least I'll be at 2.7 vols which is well within the ballpark.

My suspicion is that my CO2 vols are actually going to be nearer the 2.45 vols when I start this process.

Any ideas?

I'm on vacation, so might not get to this right away (a week or so probably.)

Brew on

 

[DuncB]

I'm on vacation, so might not get to this right away (a week or so probably.)

Brew on

Have a great time.
I'm in no hurry whatsoever. It'll take 4 weeks or so to condition anyway before I test a bottle.