Abstract: A biological process includes the step of producing a substantially continuous foam of gas bubbles in a liquid capable of undergoing a biological process utilizing prokaryotic or eukaryotic cells. The cells are introduced into the foam after the foam is produced and maintained in the foam under conditions effective to carry out the process. A reaction product of a biological process utilizing a foam culture medium is recovered by subjecting the foam to a pressure change after maintaining the cells in the foam culture medium under conditions effective to sustain the process. An apparatus for carrying out a biological process includes a foam production chamber having one or more inlets for introducing a gas and components of a culture medium. The chamber is adapted for producing a foam of bubbles of the gas in the culture medium. A plug-flow reactor is positioned to receive foam from the foam production chamber as a continuously flowing plug.