Lesson 2 - Gas Laws

Welcome back. So, what were your thoughts?

Four of the most common gases used in a brewery are:

• Carbon dioxide (CO₂)

• Nitrogen (N₂)

• Oxygen (O₂)

• Air

You may also have considered other gases such as methane, propane, and chlorine dioxide.

Let us now consider their more common uses in the brewery.

Carbon dioxide (CO₂)

In addition to yeast producing CO₂ during fermentation, we frequently recover it from fermentation and purify it for various uses within the brewery and at times for sale as a co-product. Breweries which do not practice the recovery of carbon dioxide, generally the small craft breweries, may purchase carbon dioxide for use in the brewery.

Uses of carbon dioxide include:

• Carbonation of beer and blending water

• As a purge gas to exclude air/oxygen from the process through the purging of vessels, containers, and filter powders

• Stripping of oxygen from blending water and unwanted wort volatiles during wort boiling

Nitrogen (N₂)

Atmospheric air contains around 78% by volume of nitrogen. Industrial and brewery use nitrogen is typically:

• Purchased in bulk and produced by air liquefaction (essentially cooling air at elevated pressures and low temperatures to selectively separate nitrogen from air).

• Produced in smaller quantities on-site using a nitrogen-generator which typically operates on the principle of pressure swing adsorption. This is the use of a selective adsorbent material which removes oxygen from pressurised air. The adsorbent is contained in two columns where each column is pressurised and depressurised during operation, hence the pressure swing.

Uses include nitrogenation of beer and purging of air/oxygen from vessels and containers (although this is less common than the use of CO₂).

Oxygen (O₂)

Atmospheric air contains around 21% by volume of oxygen. Brewery oxygen is typically produced using techniques similar to that for nitrogen, namely bulk purchase (air liquefaction) and small-scale on-site production using pressure swing adsorption.

Uses include oxygenation of wort prior to fermentation and yeast propagation.

Air

Atmospheric air is readily available around us (fortunately for us, as we are aerobic respirers!). As mentioned previously, it contains around 78% and 21% by volume, nitrogen, and oxygen, respectively. It can be produced on-site by either:

• Low pressure using blowers (e.g. a Roots blower)

• High pressure through the use of a compressor

In both cases, particulate filtration would be required.

Uses of air include aeration of wort prior to fermentation, yeast propagation, activation of pneumatic cylinders and pneumatically controlled valves, pressurisation of air bladders in a mash filter, and transport of lauter tun spent grains.

We have briefly covered four of the more common brewery gases. However, we might come across some more unusual gases in a brewery, perhaps in the quality control laboratory. Whatever the gas, they behave to a greater or lesser extent according to particular laws. By laws, we mean mathematical equations so we shall look at these next.