Characterizing ripening of Gruyère de Comté: Influence of time × temperature and salting conditions on eye and slit formation

Abstract Gruyere de Comte is a Swiss-type, hard cheese, made of raw milk and produced exclusively in a limited area, in the East of France. Comte cheese is regularly salted on the surface throughout the ripening period, with simultaneous rubbing. This process leads to an important bacterial surface growth (10 11 CFU/g), a production of NH 3 (50 ppm), and a regular increase of the salt level. The kinetics of salt intake and its final level strongly influence the propionic fermentation and eye formation, as well as the primary proteolysis. Hydrolysis of α s 1 - CN decreases regularly with the salt level, whereas plasmin activity is maximum at 2·3% salt/moisture. Variations in the ripening time × temperature cycle influence the rate of hydrolysis of α s 1 - CN and to a lesser extent of β-CN. The improntance of the propionic fermentation increases with the temperature of ripening. The modifications of the rheological properties of Comte during ripening appear to be time × temperature dependent. Slit formation is closely related to cheese composition and also to the nature and extent of proteolysis. It was shown that when several of the following physicochemical characteristics: low moisture, high fat, high NaCl, low calcium and high level of protein breakdown are associated, the rheological properties are modified in such a way (increase of the shortness), that the cheeses are more likely to have slits. The relative importance of the anisotropy of the rheological properties explains the direction of the slits which are always parallel to the surfaces. A high correlation (r = 0·96) was found between the log of the fracture strain difference and the slit intensity. From all the results obtained in various studies, it appears that monitoring both the nature and extent of proteolysis through milk quality, cheese making, and ripening conditions, is a major challenge to produce regularly high quality Comte cheese.