  Colloidal gels undergo a phenomenon known as physical aging, i.e., a
continuous change of their physical properties with time after the gel point.
To date, most of the research effort on aging in gels has been focused on
suspensions of hard colloidal particles. In this letter, we tackle the case of
soft colloidal "micelles" comprised of proteins, where gelation is induced by
the addition of an enzyme. Using time-resolved mechanical spectroscopy, we
monitor the viscoelastic properties of a suspension of colloidal micelles
through the sol-gel transition and its subsequent aging. We show that the
microscopic scenario underpinning the macroscopic aging dynamics comprises two
sequential steps. First, the gel microstructure undergoes rapid coarsening, as
observed by optical microscopy, followed by arrest. Second, aging occurs solely
through a contact-driven mechanism, as evidenced by the square-root dependence
of the yield stress with the elastic modulus measured at different ages of the
gel. These results provide a comprehensive understanding of aging in enzymatic
milk gels, which is crucial not only for a broad range of dairy products, but
also for soft colloids in general.
