This paper addresses the issue of analysing the results given by viability sets, which represent all the viable states of a dynamical system. Viability sets and capture basin are a relatively new method to study complex dynamical systems, focusing on the preservation of some properties of the system (constraints in the state space) rather than on the possible stable states and equilibria. The viability set delimits the area of the state space where there is always a list of controls that allows the system to verify indefinitely the constraints. A viability set represents a huge amount of information about the system it studies. We propose here a geometric study of viability sets. This study is applied to the viability tube (the sequence of viability set over time) of a food process.