How To Tell if CO2 Tank Is Empty – A Clear, Simple Guide

For me, there are few things worse than a flat pint of draft beer (it’s just a nasty rumor that we Brits like warm flat beer!). The anticipation of that perfect IPA pouring from the tap, just to be presented with a lifeless beer lacking all that essential fizz that normally adds to the flavor.

Flat beer is normally down to a lack of CO2 in the beer. If it’s a bottled beer maybe it wasn’t force carbonated enough, or perhaps not enough sugar was added in the priming stage. But when it comes to draft beer, it’s mainly down to the CO2 which is stored in that canister next to the keg.

Perhaps it is a leak in the system, or maybe the beer is past its sell-by date, but most times it will be down to an empty or almost empty CO2 tank. How do you know when your CO2 tags cylinder is empty or almost empty?

Although most people would say to check the pressure gauge on the side of your regulator, this method isn’t always 100% accurate. The regulator gauge could be broken, not all gauges are made the same and pressure can vary depending on the temperature and altitude of the local environment.

Are there any other ways you can check if your CO2 gas cylinder is empty or soon will be? Can you just shake it like you would with any other container containing liquid or gas? How much more should it weigh if it still has gas in it?

Why is Carbon Dioxide Important in Beer?

pouring beer into a glass, the foam pours out of the glass
Photo by Lorenzo Rui on Unsplash

Carbon dioxide (CO2) plays an important role in beer, as it provides the carbonation and the characteristic bubbles that are present in beer. During the brewing process, yeast ferments the sugars present in the wort (a mixture of malted barley, hops, and water), which produces alcohol and CO2 as byproducts.

Brewers typically add additional CO2 during the bottling or kegging process to achieve the desired level of carbonation. The amount of CO2 added will affect the taste and mouthfeel of the beer, with higher levels of carbonation resulting in a more effervescent and refreshing beer.

CO2 also plays a role in preserving the beer’s freshness by acting as a natural barrier against oxygen. Oxygen can cause the beer to oxidize, which can result in off-flavors and a stale taste. By maintaining the proper levels of CO2, brewers can help extend the shelf life of their beer and ensure that it tastes as intended when it reaches consumers.

pressure gauge half filled with liquid
Photo by Richard Burlton on Unsplash

As a homebrewer, it is important to have a reliable and efficient system for dispensing CO2 into your beer kegs.

However, it can be difficult to tell when your CO2 tank is running low or is completely empty. Let’s take a look at some tips and tricks for determining whether your CO2 tank needs to be refilled or replaced.

Check the Pressure Gauge

Manometer mit CO2 Flasche
Image Courtesy of Wiki Commons

The most common way to determine whether your CO2 tank is empty is to check the pressure gauge. Most CO2 tanks will have a pressure gauge attached that displays the amount of pressure inside the tank.

Typically, a full CO2 tank will have a pressure reading between 800 and 900 psi (pounds per square inch), depending on the temperature of the tank. As the tank empties, the pressure will drop. Once the pressure drops below 200 psi, it is time to refill or replace the tank.

It is important to note that the pressure gauge may not always be accurate, especially if it is old or damaged. If you suspect that the gauge is not displaying the correct pressure, you can use one of the other methods described below to confirm whether the tank is empty.

The other problem with the gauge on the regulator on CO2 cylinders is that they will not tend to drop into the red zone before the gas is already nearly empty. By then it can be too late to do anything about it. Because liquid carbon dioxide cylinders always store the CO2 as a liquid, the pressure gauge will always appear to register full until all of the liquid has been used.

How To Read a CO2 Cylinder Pressure Gauge

Reading a pressure gauge on a CO2 regulator is a straightforward process, but it’s important to know what the different parts of the gauge represent. Here’s a step-by-step guide to reading the pressure gauge on a CO2 regulator:

  • Locate the pressure gauge on the regulator. It’s usually a round dial with numbers and markings on it. Some CO2 cylinders will use a dual gauge regulator, There is always a supply regulator gauge that shows the pressure going out to the dispensing system. The container pressure gauge shows the level of pressure of the carbon dioxide in cylinders (normally you would refill when this drop below 120 PSI).
  • Look at the numbers on the dial. They indicate the pressure of the CO2 inside the regulator or the pressure going to your keg, typically measured in pounds per square inch (PSI). The numbers usually range from 0-60 PSI for the supply gauge or 0-2000 PSI for the tank pressure.
  • Identify the red area on the dial, which is typically marked with a red line or shaded in red. This is the “danger zone” and indicates that the pressure is too high, which can be dangerous and may cause equipment failure.
  • Identify the green area on the dial, which is typically marked with a green line or shaded in green. This is the “safe zone” and indicates the appropriate pressure range for carbonating or dispensing beer.
  • Determine the appropriate pressure for your specific application. The ideal pressure will depend on the style of beer, temperature, and carbonation level desired. Consult your brewing recipe or a beer carbonation chart to determine the appropriate pressure.
  • Adjust the pressure by turning the adjustment knob on the regulator, typically located on the top of the regulator. Turn the knob clockwise to increase the pressure or counterclockwise to decrease the pressure.

How To Check if Your Tank Is Empty by Weight

Image by Kalhh from Pixabay

Many would argue the only true way to know if your CO2 tank is empty is to weigh it. The gauges on the side of the tank are more like a fuel light that comes on in your car than an actual measure of the gas remaining in the tank.

On the side of every CO2 cylinder, even the old-style cylinders, you will find a Tare Weight, usually indicated by TW, followed by a number in LBs or KGs. This is the actual weight of an empty CO2 tank. If you can’t see the TW, you could always google it.

You can use a bathroom scale or a dedicated scale to weigh the tank. Once you subtract the cylinder weight from the weight displayed on the scales, this should give you the amount of CO2 in the canister. If you are actually using a smaller portable cylinder, you could weigh it without even disconnecting it from your kegerator, but remember to take into account the weight of any gauges or keg connections attached to the cylinder.

For example, if the Tare Weight (TW) is 8.5 lbs and the actual weight on the scale is 12.5 lbs, then you have 4 lbs of CO2 remaining. You should allow for roughly a quarter of a pound each way on both the Tare Weight and the CO2 weight using this method to allow for differences in pressure or temperature.

It is important to note that the weight of the tank will vary depending on the temperature and pressure of the tank. Therefore, it is a good idea to weigh the tank when it is at room temperature and has not been recently used.

Does Frost on the Side of a CO2 Tank Indicate It’s Empty?

Yes, you can also look for frost on the CO2 tank or the regulator to determine whether the tank is empty. When CO2 is released from a pressurized tank, especially larger cylinders, it expands rapidly and cools down quickly.

If the tank is empty or close to empty, you may notice frost forming on the outside of the tank or the regulator. This is a sign that the tank is releasing its last bit of gas and needs to be refilled or replaced.

Other Signs Your CO2 Tank is Empty

Speed of Beer Flow

Look to check how quickly your beer flows out of the faucet head as you pour it. If the beer is flowing out of the faucet head in an unusually slow manner this could be a sign your CO2 cylinder is empty, as the CO2 is responsible for pushing the beer out of the keg and into the faucet.

It could also be a sign of a faulty regulator too, so listen carefully to the regulator to see if you can hear any gas hissing as it escapes.

If the tank is empty, there will be no gas flowing through the system, and you will not hear any hissing or bubbling sounds. However, if the tank is not completely empty, you may hear a faint hissing sound as the last bit of gas escapes from the tank.

You can also check the flow rate by disconnecting the keg from the regulator and turning on the CO2 valves. If there is no gas flowing through the cylinder valve to the regulator, it is likely that the tank is empty.

Flat or Off Flavors in the Beer

If your beer tastes flat or has lost much of its flavor, this is another sign your CO2 tank is empty and probably has been for a while. Remember CO2 not only maintains the carbonation of kegerator beer but can also act as a barrier against oxidation of the beer.

A Larger Foam Head on Beer

If the beer you pour from your kegerator appears to have a foam head that is made of larger, soapy-looking bubbles or the foam dissipates very quickly, this is another sign of an empty CO2 cylinder.

How Long Should a CO2 Cylinder Last?

That depends on both the size of the cylinder and the keg it is being used with. As a general rule with a 5-pound cylinder, you should expect it to last between 15 – 22 Corny Kegs with a 5-gallon capacity.

If used with a larger half barrel of 15.5 gallons you should expect it to last 5 – 7 kegs. This can vary depending on the type of beer served and whether the CO2 cylinder is used for quickly force carbonating a beer (which uses more CO2) or just dispensing the beer.

How Many Kegs Form a CO2 Cylinder?

 2.5 Pound Cylinder5 Pound Cylinder10 Pound Cylinder
Corny Keg (5 Gallons)7 - 1115 - 2231 - 44
Quarter Barrel (7.75 Gallons)5 - 710 - 1420 - 28
Half Barrel (15.5 Gallons)2 - 45 - 710 - 14

Final Thoughts

In conclusion, there are several ways to determine whether your CO2 tank is empty when brewing beer. Checking the pressure gauge, weighing the tank, listening for gas, checking the flow rate, and looking for frost are all effective methods for determining whether the tank needs to be refilled or replaced.

It is important to check the tank regularly and have an extra cylinder on hand to ensure that you never run out of CO2 during a force carbonation process of the beer or just simply serving it. It would be horrible to have a nearly full keg of IPA just sitting there with no way of getting it out of the keg!

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