Jetting is a method used to expel air from the headspace of a bottle or other container of beer. This method involves using a fine stream of high pressure, and often high-temperature sterilized water, to energize the beer, causing a controlled rise of bubbles and foam from deep within the beer through the headspace just as the closure is placed on the container. Often called “fobbing,” this practice has evolved with the development of high-speed packaging lines. Earlier systems included bottle knockers and ultrasonic vibrations and newer systems have experimented with the use of CO₂ or liquid nitrogen rather than water. See carbon dioxide and nitrogen.

The most common jetting practice involves a system that treats potable water to deal with any substances that may affect the beer or the system. Chlorine, sediment, and minerals should be removed prior to entering the system to avoid their negative effect on the beer and the machinery. The water is then pressurized to between 10 and 17 bar (145 to 246 psi) using an adjustable high-pressure air pump that feeds water through an in-line heating source to a nozzle of 0.20 to 0.25 mm (0.008 to 0.010 inch). Pressure, nozzle size, and the distance of the jetter from the capper are all adjusted based on package size and line speed. The settings should be evaluated based on the depth of the jet stream penetration, the control of the foam rise, and finally on the resulting headspace air and total package oxygen results. Nozzles should be replaced or cleaned regularly to ensure a tight, high-energy stream. Out of control jetting can result in air entrapment as well as an unacceptable loss of liquid and improper fill levels.