Beer Carbonation

The next major process that takes place after filtration and prior to packaging is beer carbonation. Carbon dioxide not only contributes to perceived "fullness" or "body" and enhances foaming potential it also acts as a flavor enhancer and plays an important role in extending the shelf life of the product.

The level of dissolved carbon dioxide in beer following primary fermentation varies as a result of a number of parameters such as temperature, pressure, yeast, type of fermentation vessel, and initial wort clarity. Typically, carbon dioxide levels range from 1.2 to 1.7 volumes of carbon dioxide per volume of beer (v/v) for non-pressurized fermentations. Consequently, carbon dioxide levels need adjustment, unless the beer has undergone secondary fermentation. Common practice is to raise the carbon dioxide level between 2.2 and 2.8 v/v and possibly more prior for bottled and canned products. The carbon dioxide levels for kegged beer typically range from 1.5 to 2.5 volumes.

Principles of Carbonation

The time required to reach a desired carbon dioxide concentration depends on a number of physical factors. Temperature and pressure play an important role in determining the equilibrium concentration of carbon dioxide in solution. Increasing the pressure leads to a linear increase in carbon dioxide solubility in beer. Decreasing the temperature gives a nonlinear increase in carbon dioxide solubility in beer. Consequently, the equilibrium concentration cannot be attained without either increasing the pressure or decreasing the temperature. Thus, the closer the carbonating temperature is to 0°C and the higher the pressure, the greater the carbon dioxide absorption. The amount of carbon dioxide that dissolves is a function of time, with the rate decreasing exponentially as equilibrium is approached.

Methods of Carbonation

• Secondary Fermentation

The traditional method involves carbonating the beer during secondary fermentation at low temperatures and under counter-pressure. The beer transferred to the conditioning tank should have at least 0.5 to 1.0°P of fermentable extract and be placed under pressure from 12 to 15 psi in conditioning tanks. While in the tank, the remaining extract ferments and creates sufficient carbon dioxide to saturate the beer to equilibrium.

• Kraeusening

Another carbonation technique involves priming the green beer with wort-primed beer, a process referred to as "kraeusening." As the second fermentation takes place, the excess carbon dioxide is bled off until the fermentation end point is obtained.

• Bottle-Conditioning

Before the advent of artificial carbonation, brewers carbonated beer by adding priming sugars (glucose, dextrose, and invert sugar) to the bottle for conditioning.

• Mechanical

Mechanical carbonation is accomplished either by in-line or in-tank techniques. Carbon dioxide may be purchased from suppliers of industrial gases. Alternatively, carbon dioxide may be recovered from fermentation vessels and then purified, liquefied, and stored until needed for carbonation. However, this collection system can be too expensive for most craft brewers.

In-Line Carbonation

In-line carbonation involves injecting carbon dioxide into the beer through a fritted stainless steel diffuser between the outlet of the filter and the bright beer tank.

In-Tank Carbonation

In-tank carbonation involves injecting carbon dioxide through either a submersed ceramic or sintered stainless steel stone at the bottom of the tank until a given backpressure is reached.