Methods of Carbonation
There are several methods used in carbonating beer including secondary fermentation, kräusening, bottle- and cask-conditioning, and forced carbonation.
The traditional method involves carbonating the beer during secondary fermentation (i.e., lagering) at low temperatures and under counter-pressure. The beer transferred to the conditioning tank should have at least 0.5 to 1.0 degree Plato of fermentable extract and be placed under pressure from 12 to 15 pounds per square inch (psi) in conditioning tanks (Patino, 1999). While in the tank, the remaining extract ferments and creates sufficient carbon dioxide to saturate the beer to equilibrium. Munroe reports that if the pressure is too high during secondary fermentation, yeast growth may be affected and change the flavor characteristics of the beer (Slater, 1989).
Another carbonation technique involves priming the green beer with wort-primed beer, a process referred to as kräusening.
Bottle- and Cask Conditioning
Before the advent of artificial carbonation, brewers carbonated beer by adding priming sugars (glucose, dextrose, and invert sugar) to the bottle or cask for conditioning.
Forced carbonation is accomplished either by in-line or in-tank techniques. Some brewers report that uses of forced carbonation actually has a greater influence on reducing acetaldehyde levels than does kräusening the beer.
In-line carbonation involves injecting carbon dioxide into the beer through a fritted stainless-steel diffuser (Figure 16.1) between the outlet of the filter and the bright beer tank. It cannot be done upstream from DE filtration because carbon dioxide bubbles would disturb the filter bed (Meheen, 1994).
In-line Carbonation Injector. Control of this process may be hard to achieve under craft brewery applications. The best way to use in-line carbonation for a craft brewery is to set up a portable system and mount it over the re-circulating pump (Black, 1989).
In-tank carbonation involves injecting carbon dioxide through either a submersed ceramic or sintered stainless steel stone (Figure 16.2) at the bottom of the tank until a given backpressure is reached. The introduction of minutely divided gas directly into the bottom of a tank closely resembles the gas generating action of beer fermenting under pressure. Reportedly in-tank carbonation brings about more uniform carbonation and eliminates the stratification of gas content that is often prevalent with other methods.
Carbonation Process. The first step is to determine the temperature of the beer and the desired carbonation level, in order to arrive at the required saturation pressure. The next step is to calculate the wetting pressure (WP) of the carbonation stone. The wetting pressure is the psi needed to produce bubbles on a carbonation stone when wetted. For most stones, this wetting pressure is between 2 to 8 psi. To calibrate the stone, submerge it in water at the same orientation as it would be in the tank and slowly increase the psi until bubbles begin to flow, record the psi, then slowly decrease the carbon dioxide until the bubbles stop completely. Record this last psi reading and take the average of these two readings to determine the wetting pressure psi.
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