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Once beer is fermented, contact with oxygen (or air, as air contains 21% oxygen) can spoil the flavour and reduce shelf life. Therefore, beer is moved around the brewery and packaged under a 'blanket' of process gas such as carbon dioxide or nitrogen or a mixture of the two.
This is particularly important once the beer has been carbonated (or nitrogenised). Apart from excluding oxygen, a gas pressure above the surface of the beer ensures that dissolved gas does not come out of solution. Examples of the use of mixed gases in brewing include counter pressure keg racking and beer dispense.
Before beer is pumped into a keg, the air that the keg contains is replaced with a pressurised atmosphere of inert gas or a gas mixture. This is carbon dioxide and nitrogen mixed in proportions to suit the product. Where a nitrogenised beer is involved, the use of mixed gas is essential in order to keep both gases in solution. It is at this point in the process that most large UK brewers rely on WITT gas mixing technology and expertise.
The MG range of WITT gas mixing panels supply mixed gases at flow rates between 50 (1765 SCHF) and 500 cubic meters an hour (17654 SCFH). Mixtures can be anything between 0 - 100% and are accurate to +2% or better. Adjustment of the mixture is achieved either manually or electronically, which in the latter case can be carried out remotely if required. The mixture can be controlled using WITT gas analysers to meet quality assurance requirements.
Using gas pressure for beer dispense is not a new idea. In fact it has been common practice since the introduction of kegged beer in the late 1950's and has several advantages; it avoids the use of expensive pumps, it stops the beer going flat and, as the keg empties, prevents contact with air and therefore maintains quality over the life of the broached keg.
However, using only carbon dioxide has one major disadvantage. If the beer has to be pushed a long way or lifted from a deep cellar, then the gas pressure needed to produce the required flow at the dispense tap is often much greater than that required just to maintain carbonation (equilibrium pressure). The result being over-carbonation of the beer and inevitable wastage as the beer 'fobs' as it dispensed in the bar.
A very simple and efficient way of overcoming this problem is to use mixed nitrogen and carbon dioxide. In fact, if the beer concerned is a nitrogenised ale or stout, then the addition of a nitrogen component to the dispense gas is essential in order to maintain the desired level of nitrogen dissolved in the product.
If a mixture of say 50% nitrogen and 50% carbon dioxide is used at say an absolute pressure of 2,8 bar (40 psi) then half this pressure 1,4 bar (20 psi) is provided by the carbon dioxide and half by the nitrogen. Thus, by varying the mixture and therefore the partial pressures of its' components, levels of both carbonation and nitrogenisation can be easily maintained to suit the product no matter what pressure is required for efficient dispense.
One way of doing this is to use cylinders of pre-mixed gases. This however can be expensive and starts to become complicated and cumbersome if each draught product requires a different mixture. These problems can be overcome by using just one cylinder of carbon dioxide and one of nitrogen (or indeed any other source of nitrogen such as an separator) and a WITT KM 20 gas mixer designed specifically for this purpose. This way, any number of tailor-made gas mixes can be produced to exactly suit the products and physical layout of the bar and cellar or cold room.
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