Producing a foam involves the generation of a protein
film surrounding a gas bubble and the packing of gas
bubbles into an overall structure. One of the first differences
seen between studies of interfacial protein films and foams
is the lack of stability of the latter. While a model interface
can be observed for hours or days to establish equilibrium, a
foam made with whey or egg white proteins starts changing
within minutes of formation. Therefore, properties of
protein foams are measured under non-equilibrium conditions,
complicating interpretation within and between
investigations. However, some general observations can be
made.