a b s t r a c t The end-use value of durum wheat (Triticum turgidum L. subsp. durum (Desf.) Husn.) is mainly governed by its grain protein concentration and composition. Adjustment of variables to compensate for inter-annual and location variations in semolina quality leads to high cost for processors in the wheat industry. A better understanding of the mechanisms governing environmental variations of grain protein composition is thus required. Here, a field experiment was setup in a Mediterranean environment with the aim to analyze the effect of sowing date and nitrogen (N) fertilization on the dynamics of grain dry mass, water, protein composition and glutenin polymer size distribution for durum wheat cv. Creso. The results indicated that (1) grain dry mass accumulation was related to grain water concentration and stopped at 44.9% independently of the growing conditions and N supply; (2) during the grain filling period as well as at ripeness maturity, the quantity of the different protein fractions scaled with the quantity of N per grain; (3) SDS-extractable glutenin polymers were produced continuously until the same grain water concentration as the dry mass deposition was reached; (4) SDS-unextractable polymeric proteins were found as early as 7 days after anthesis and their rate of accumulation increased sharply when grain dry mass was 60% of its final value and proceeded at a constant rate until ripeness maturity, thus suggesting that the insolubilization of glutenin polymers is not directly related to the rapid loss of water after physiological maturity, but rather to the continuous dehydration of the grain.