1. In an apparatus for expanding a food product comprising means for mixing said food product with a gas; pump means connected to supply said food product to said mixing means under pressure; means for introducing said gas into said mixing means downstream of said pump means at a pressure greater than that at which said pump supplies said food product; and pressure-regulating outlet valve means downstream of said mixing means through which a mixture of said food product and said gas emerges from said mixing means; the improvement which comprises pressure responsive control means responsive to the pressure of said food product upstream of said gas introducing means but downstream of said pump means, said control means being connected to said pressureregulating valve means to control the opening of said valve means in dependence on said food product pressure and thereby maintain a substantially constant pressure drop between said pump and outlet valve.

8. An apparatus for preparing a volume inflated dairy product comprising stabilizers with a substantially constant expansion ratio by dissolution in said product of a high pressure gas having a low solubility in water, comprising metering high pressure pump means for producing a predetermined rate of flow of said product; injection means downstream of said pump means for injecting said gas into said product at a higher pressure than that of said product; mixing means downstream of said injection means comprising a smooth tube having a small diameter and a substantial length; pressure detector means located upstream of sAid injection means and downstream said pump means; and a pressure regulating valve means located at the end of said smooth tube and operatively connected to said pressure detector means so that said valve is actuated in dependence on said product pressure.