# How can I measure the CO2 volume in headspace?

### Help Support Homebrew Talk:

#### Salmeen

##### New Member
For example if I want to measure the CO2 volume in the headspace of a 500mL bottle of carbonated water? How can I do that? Thanks in advance

#### Qhrumphf

##### Stay Rude, Stay Rebel, Stay SHARP
Are you asking how to measure the carbonation level of the water (volumes of CO2), or the physical volume of the headspace, or the concentration of CO2 solely in the headspace and NOT the water?

#### bracconiere

##### Jolly Alcoholic
HBT Supporter
weight or volume are the only ways to do it...PSI is a factor with volume....at least that's what i know so far....

OP
OP

#### Salmeen

##### New Member
the concentration of CO2 in the headspace I mean sorry for the confusion

#### bracconiere

##### Jolly Alcoholic
HBT Supporter
@doug293cz knows gasing laws.....if this is carbonated water...well anyway....i'd let it sit after weighing it, open it to see how many grams it loses.. calculate co2 that way....

#### VikeMan

##### It ain't all burritos and strippers, my friend.
the concentration of CO2 in the headspace I mean sorry for the confusion

Do you actually want to measure it, or do you want to estimate it, based on, for example, the water's (estimated) CO2 volumes?

#### VikeMan

##### It ain't all burritos and strippers, my friend.
@doug293cz knows gasing laws.....if this is carbonated water...well anyway....i'd let it sit after weighing it, open it to see how many grams it loses.. calculate co2 that way....

You'd need all of the CO2 in the headspace to leave, all the water's CO2 to stay in the water, and no other gases from the air getting into the headspace (and water). None of these requirements would be met.

#### doug293cz

##### BIABer, Beer Math Nerd, ePanel Designer, Pilot
Staff member
Mod
For example if I want to measure the CO2 volume in the headspace of a 500mL bottle of carbonated water? How can I do that? Thanks in advance
The CO2 volume in the headspace is equal to the headspace volume. All gases expand to completely fill their enclosing container. If you have a mixture of gases in the headspace, and there are different amounts of each gas, the volume of each is the equal to the volume of the headspace, and the total volume of all the gases combined is also equal to the headspace volume. That's a fundamental property of gases.

There are some things you can measure or calculate, such as the amount (mass) of a particular gas in the headspace, the concentration of a particular gas in the headspace, the partial pressure of a particular gas in the headspace, etc.

What do you intend to do with the information. Knowing this should help determine which measurement/calculation needs to be done.

Brew on

#### jddevinn

##### Got 99 Problems but beer ain't one
HBT Supporter
Gasses don't mix like liquids because they expand to fill the container. If you have a 500ml bottle that contains only O2 and CO2, no matter what the ratio of the two components you have 500 ml of both O2 and CO2. (This doesn't seem correct to most people at first glance, but if you had a 50:50 by weight mix of O2 and CO2 in a 500 ml container and 'magically' moved all of the CO2 out and into a separate 500 ml container. Then you have a 500ml container of O2 and a separate 500ml container of CO2)

The ratio of the gasses is determined by mass (not volume) and typically expressed either as mass ratio (mole ratio) or partial volume.

....

What are you ultimately trying to determine?

#### Qhrumphf

##### Stay Rude, Stay Rebel, Stay SHARP
I'm still not sure. I think the poster is looking for something along the lines of PPM or mass or mols of CO2 solely in the headspace. But I'm not sure why.

One could directly measure the CO2 of the liquid using very expensive equipment (a Zahm and Nagel can and bottle piercer running approximately \$1000 the cheapest option I'm aware of), and then calculate from there based on temps and pressures (I don't know the science and math there well enough, Doug probably does...). Or I presume use even more expensive lab equipment. But if one is trying to determine CO2 in relation to other gasses as well, Zahm won't cut it.

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#### Qhrumphf

##### Stay Rude, Stay Rebel, Stay SHARP
Rather, I *presume* the OP is attempting to measure the carbonation of the water itself and is confusing terms with what they're asking. To which, see above about testing equipment.

(Based on other posts by OP about trying to carb seltzer water in a keg, I assume they're trying to see what their bottled seltzer of choice is carbed to as a standard).

HBT Supporter

#### Qhrumphf

##### Stay Rude, Stay Rebel, Stay SHARP

While I've never seen that particular device before, Taprite has a similar device to compete with the normal Zahm carb tester, and the consensus I've read is "you get what you pay for". Zahm's products are even poor compared to options like Anton Paar, but instead of a few thousand dollars you're looking at twenty thousand dollars.

(Yours doesn't SAY it's Taprite but it the design is identical so I assume it is EDIT: actually it does say it's Taprite...)

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#### jerrylotto

##### Well-Known Member
Having the tare weight and full weight of every keg recorded makes it pretty easy to figure out headspace at any point just by dividing the weight - tare by the full weight - tare. You can estimate the full weight with water.

#### VikeMan

##### It ain't all burritos and strippers, my friend.
You can estimate the full weight with water.

If you measure the full weight with water, and thus know how much the water weight is (after subtracting the tare weight), you can calculate what the (full) beer weight would be by multiplying the water weight by the beer's specific gravity. It may not make much difference, but if you're going to all the trouble anyway, it's an easy added step.

#### jerrylotto

##### Well-Known Member
And of course, you need to know the total volume of the keg as well. After the full water weight, measure that volume when you empty it or just calculate it - 62.4 lb / cu ft

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#### jerrylotto

##### Well-Known Member
If you measure the full weight with water, and thus know how much the water weight is (after subtracting the tare weight), you can calculate what the (full) beer weight would be by multiplying the water weight by the beer's specific gravity. It may not make much difference, but if you're going to all the trouble anyway, it's an easy added step.
true dat!

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