Lesson 3 - Gas Laws SAQ

*List four key brewery gases. Describe how they are commonly produced, and list uses for them in the brewery.

Response:

1.    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 or for sale as a co-product. Breweries which do not practice recovery of carbon dioxide, generally the small craft breweries, may purchase carbon dioxide for use in the brewery.

Uses include:

• Carbonation of beer and blending water

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

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

2.    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 – 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 principle.

Uses include:

• Nitrogenation of beer

• Purging of air/oxygen from vessels and containers (although this is less common than the use of CO₂)

3.    Oxygen (O₂)

Atmospheric air contains around 21% by volume of oxygen and brewery use 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

• Yeast propagation

4.    Air

Atmospheric air is readily available around us (fortunately for us, as we humans are aerobic respirers). As mentioned previously, it contains around 78% and 21% by volume, nitrogen, and oxygen. Air can be produced by:

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

• High pressure through the use of a compressor.

In both cases, particulate filtration would typically be required.

Uses 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

• Transport of lauter tun spent grains