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The Role Of Oxygen Deficiency Monitoring In Breweries

Breweries are home to a cornucopia of chemical reactions. From fermentation to drying to filtration, many of the stages of the brewing process involve different chemistry and, in some cases, the production of gases. While many of these gases may not be highly toxic in themselves, large volumes of them can pose serious health and safety risks and necessitate the use of extensive gas monitoring equipment in breweries.

The fermentation process is one of the key reaction steps in the production of alcoholic products. It is the concentrations of chemical side products produced during this reaction that affect the final flavor profile of the product1 and the rate at which fermentation occurs influences the overall ethanol concentration in the final product.2

Fermentation occurs under anaerobic, or oxygen-deficient, environments. Under such conditions, yeast breaks down glucose in the brewing mixture into ethanol, producing carbon dioxide as a side product. In addition, smaller amounts of hydrogen and methane gas may be produced.

Although it is unlikely a worker would encounter the oxygen-deficient environment of a closed fermentation vat if there is a leak from such a vessel, large amounts of carbon dioxide could be released. As this is an odorless, colorless gas, a leak can easily go unnoticed. Open fermentation vessels are more problematic as the headspace above such vessels can reach very high carbon dioxide concentrations.3

Carbon dioxide can cause dizziness and nausea at low concentrations and lead to death by asphyxiation (due to the displacement of oxygen) at higher concentrations making it a legal requirement to have gas monitoring equipment in areas where carbon dioxide is used or produced.4

As well as the difficulty in noticing whether leaks occur, what makes carbon dioxide particularly dangerous as an asphyxiant is that it is heavier than oxygen and so will pool in low-lying areas, displacing the oxygen there. This means that even if the areas around the fermentation tank itself are not affected, nearby basement or lower level areas can still be at risk for small leaks.

Gas Detection or Depletion?

There are several ways of adhering to health and safety legislation surrounding carbon dioxide production. This can be through the use of gas detectors, that monitor the concentration of a particular gas, or through oxygen depletion sensors.

While gas monitors can be useful for the detection of leaks, sensors are typically designed for the detection of only one type of gas. As the main risk in breweries is usually asphyxiation, caused by a lack of oxygen, the use of oxygen depletion sensors instead may be more appropriate.

Oxygen depletion sensors monitor the oxygen levels in gases (or in this case, the room air) and are usually connected to some kind of alarm system which sounds when the oxygen level drops too low. There are different kinds of oxygen depletion monitors, but some such as zirconium oxide oxygen sensors, rely on the presence of a reference oxygen sample to operate correctly. Sometimes the oxygen reference gas can be generated in situ, but many sensors require an external gas feed for refilling.5

Oxygen References

Many breweries may not necessarily be equipped for the safe storage and handling of large, heavy pressurized gas cylinders either. An attractive alternative to large cylinders are products such as Air Product’s non-refillable, small gas cylinders.6 They are available in small volumes (down to 34, 58 and 110 Gaseous litres) and gas are available at the high specifications needed for the most accurate reference measurements. As well as being more portable and easier to handle, Air Product’s cylinders are a good way of circumventing the health and safety issue that comes with large cylinder storage and its associated costs. This reduces the burden for refilling oxygen depletion sensors, which are an essential part of safety at any brewery site, as well as ensuring a safer workplace, without the need to introduce more specialized safety equipment for large scale gas handling.



References and Further Reading

  1. Chambers, Paul J., and Isak S. Pretorius. 2010. “Fermenting Knowledge: The History of Winemaking, Science and Yeast Research.” EMBO Reports 11(12): 914–20.
  2. Carlsen, H. N., H. Degn, and D. Lloyd. 1991. “Effects of Alcohols on the Respiration and Fermentation of Aerated Suspensions of Baker’s Yeast.” Journal of General Microbiology 137(12): 2879–83.
  3. Kobayashi, Michiko et al. 2005. “On-Line Estimation and Control of Apparent Extract Concentration in Low-Malt Beer Fermentation.” Journal of the Institute of Brewing 111(2): 128–36.
  4. HSE on CO2, (2019) http://www.hse.gov.uk/carboncapture/carbondioxide.htm, accessed 20/02/202
  5. Kimura, Shinji, Shigeo Ishitani, and Hirosh Takao. 1986. “Principles and Development of a Thick-Film Zirconium Oxide Oxygen Sensor.” ACS Symposium Series 2: 101–20
  6. Air Products Calibration Gas Cylinders (2019), http://www.airproducts.co.uk/microsite/uk/oneuse/index.htm, accessed 20/02/2020

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Leigh Greenham, Director, CoGDEM

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