This study investigates the behavior of PAL and PPO enzymes under stress conditions in grapes. Those two enzymes were chosen because: - PAL is a key enzyme in the biogenesis of aroma compounds - PPO plays an important role in anthocyanin degradation, as well as in the formation of brown pigments. PAL was found to be increase under high CO2 / low O2 concentration storage conditions; while PPO activity showed an increase after a period of time, under the same storage conditions.