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Beer Fermentation and CO2


A man pouring a beer from draught

How Does It Work? 

The next time you see a beer commercial or drink a cold draft, take the time to appreciate the importance of carbon dioxide in the brewing process.

Beer starts out as wort, a mix of water and natural grains. When Brewer’s yeast (a fungi) is added to the mix, it "eats" the starches and sugars in the wort while giving off alcohol and carbon dioxide (CO2) gas.

It is the infinitely variable combinations of water, grains, yeast, alcohol levels and the amount of carbonation which give each beer its unique color and taste.

During fermentation, the CO2 given off by the yeast was typically vented into the air. However, modern breweries now use CO2 capture systems. Once fermentation is complete, the brewing vats are sealed to build pressure and give the beer natural carbonation.

To measure the CO2 levels before and during production, brewers use our Multi Gas Sampling Data Logger. These meters may also be used to spot check CO2 levels inside vats before workers go inside to clean them.

During bottling, CO2 gas is used to pre-fill each bottle before the beer is added. This process minimizes exposure to oxygen, reduces foam, and maintains the CO2 in the beer before it is capped. In commercial breweries, even the head-space (air below the cap in the bottle) is replaced with CO2 to keep out oxygen so that the bottled beer can last longer in non-refrigerated stores. In order to test CO2 during bottling, a high-speed sensor like our SprintIR Fast CO2 sensor is used, which can measure CO2 levels 20 times per second.

One of the questions we get constantly asked is "Do you have a sensor you can put INTO the beer to measure the CO2 concentration?

The short answer is that it does not exist. The longer answer is that several companies make devices or systems that measure the pressure differential in carbonated beer to calculate CO2. But they don't measure CO2 directly.

Our ambient air CO2 sensors use Henry’s Law, which states:

“The principle that at a constant temperature the concentration of a gas dissolved in a fluid with which it does not combine chemically is almost directly proportional to the partial pressure of the gas at the surface of the fluid.”

Using Henry’s Law, you can measure the CO2 level in a liquid by measuring the CO2 in the head space above the liquid, then compute the actual CO2 level. Since the bottles are filled with CO2 before they are filled with liquid - and because CO2 is heavier than air - a high-speed sensor testing each empty bottle is full of CO2 before filling is a perfect solution.

For most beer sold in kegs, CO2 from pressurized storage tanks are used to force the beer out of the tap. To protect customers and employees that work around pressurized CO2, breweries use our Remote CO2 Storage Safety 3

Alarm. Because of the increasing use of high-pressure CO2 systems, it has become one of the most popular products we sell.

Interestingly, not every beer relies on CO2 for bubbles. The secret of Guinness Stout's creamy taste is its mix of nitrogen and carbon dioxide rather than pure CO2. The smaller nitrogen bubbles produce a smoother head. At taverns that serve Guinness on tap, they use a special nozzle that aerates the stout with nitrogen as it's poured.

In cans of Guinness this is duplicated by inserting a capsule that releases pure nitrogen when the can is opened.

CO2Meter Supports CO2 Safety In Breweries

CO2Meter has many different options available to brewers in regards to CO2 safety, whether it be a personal safety device, or a wall mounted/fixed devices, we have many products available to brewers in order to keep themselves, employees and patrons safe, while also staying compliant to the local fire codes, standards and regulations. Contact Us Online today or call us at 877.678.4259 to make your establishment CO2 Safe. 


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