  We measure the energy fluctuations of a Brownian particle confined by an
optical trap in an aging gelatin after a very fast quench (less than 1 ms). The
strong nonequilibrium fluctuations due to the assemblage of the gel, are
interpreted, within the framework of fluctuation theorem, as a heat flux from
the particle towards the bath. We derive, from a simple model, an analytical
expression of the heat probability distribution, which fits the experimental
data and satisfies a fluctuation relation similar to that of a system in
contact with two baths at different temperatures.
