Notes Screen

We have include this section as a general "How To" on subjects related to draft beer. It contains many helpful hints and other notes that we have learned from years of experience. Some of the topics include:

Example:

CO₂ / N₂ Blend / Compressed Air

In all draft systems an external force is required to push the beer through the lines and out the faucet. This is typically a pressurized gas routed into the keg exerting pressure on the surface of the beer, forcing it out of the keg. From a design standpoint, applied pressure is adjusted to maintain equilibrium with the keg’s internal pressure and flow rate is controlled with beer line restriction.

CO₂ is a natural byproduct of brewing beer and it is economical way to push beer through the beer lines. A CO₂ tank is filled to about 835 psi at 70 degrees F. and will maintain that pressure until almost empty. When CO₂ is pumped into the tank at high pressure, it becomes a liquid in the bottom of the tank. As gas is drawn off the top of the tank, some of the liquid CO₂ converts to gas, maintaining its pressure as it is used. Only after all the liquid has converted to gas will the pressure begin to drop.

Each pound of CO₂ should push one and a half kegs of beer. Therefore a 20 pound tank of CO₂ should push about 30 kegs. To determine the amount of CO₂ in a tank, simply weigh the tank, then subtract the empty tank weight (stamped on the neck of the tank) from it.

As a tank of CO₂ cools, its pressure drops. As its temperature rises, its pressure increases. This phenomenon necessitates the use of pressure release valves. This applies to beer also. As the temperature rises, the beers internal CO₂ pressure increases. This requires applied pressure to be increased to maintain equilibrium. The opposite is true when temperature decreases.

As you use the line balancer on the Draft Engineering screen 1, you will notice that the recommended applied pressure is only slightly higher than the kegs internal pressure at any given temperature. This allows the kegs to maintain their natural carbonation level. Too little pressure will allow the natural carbonation to escape from the beer causing it to go flat and lose its flavor. Too much pressure will tend to increase the carbonation of the beer, causing it to pour with too much foam. Over carbonation can also affect the flavor of the beer.

When long draw or high lift systems have problems with over carbonation because of the higher applied pressures required, it might be necessary to use a compressed air or a N2 blend. Higher pressures (pressures that exceed the beers internal pressure) should be used with a blend of inert gas such as nitrogen because it does not carbonate the beer. OnTap uses partial pressure calculations to determine the correct ratio. Very simply put, As the system restriction increases from lift and run the pressure must increase to push the beer. The CO₂ pressure is allowed to increase until it equals the internal pressure of the beer. At this point and beyond the CO₂ pressure is held constant. As additional pressure is required it is introduced with nitrogen. If the kegs racking pressure is 12 pounds for instance, but the long-draw system requires 20 pounds of applied pressure, the remaining 8 pounds is applied with nitrogen. The total pressure applied is 20 pounds, but the CO₂ partial pressure is held to 12 pounds. The ratio in the above example is 60% CO₂ and 40% N₂. If the total pressure required were only 16 pounds, the CO₂ would still be 12 pounds and the N2 would require 4 pounds. This ratio would be 75% CO₂ and 25% N₂. (12/16ths and 4/16ths) Partial Pressures are achieved using blenders. An example of such a blender is the Trumix Blender. Note that the actual partial pressure calculations are much more complex, and factor in temperature, altitude, etc.

Some blenders and premixed gasses will not provide ratios with this low a percentage of N₂. This causes the ratio of CO₂ to be too low and can allow beer to go flat. In high-volume accounts this is not usually perceived as a problem because the beer is dispensed before it can go flat. In lower volume accounts were kegs can stay on line for a week or two, the kegs will not maintain their original carbonation. This causes three problems: 1) The beer is no longer the same as it came from the brewery. 2) The beer may pour with less foam reducing the profitability for the account. 3) The account is using much more N2 than is necessary, costing them more money. (N2 is more expensive than CO₂.)

Nitrogenated beers use a different system. Please read about Nitrogenated Beers in the Notes section. More follows........