Crystallization and jamming in the traditional balsamic vinegar

High-resolution light microscopy (HR-LM) and X-ray diffractometry (XRD) were used in a non-destructive way to study the bulk structure of the Traditional Balsamic Vinegar of Modena (TBVM), an Italian specialty produced from cooked grape must and through a long aging process at room temperature. Data showed that TBV is a viscous food dispersion that may undergo solidification through equilibrium and out-of-equilibrium phase transitions including crystallization and jamming of amorphous colloids. Crystallization is due to the rearrangements of the α-d-glucose monohydrate molecules; while, jamming is caused by the crowding of amorphous long-living colloids of unidentified substances that eventually separated into a space-limited solid-like phase or into a gel network spanning the available volume. Due to their natural ability to self-associate into amorphous colloids, a role of polymeric melanoidins was also supposed into the development of vinegar bulk structure and, eventually, into its solidification.