This work described the hydration kinetics of several grains from the legumes and cereal families, which many of them were studied for the first time. In addition, some comparisons among the different hydration kinetics were performed to corroborate some hypothesis about this process. By comparing the hydration kinetics of the studied grains and fitting their data to suitable equations, the idea that this process is very complex was reinforced. It is difficult to say how intrinsic properties of the grains (color, size, specie, family, structure or composition) affect the hydration process. Some reported hypothesis about the hydration process were argued. For instance, it was demonstrated that some hypotheses about the grains hydration are not completely true: the grains with darker color seed coat do not always hydrate slower than the lighter color ones; the grains with sigmoidal behavior can hydrate faster than the grains with downward concave shape behavior; the bigger size grains sometimes hydrate slower than the smaller ones. It was concluded that the hydration process behavior and velocity are affected by many intrinsic properties of the grains (composition and structure, in a complex interaction) acting together to give the representative hydration kinetics behavior of each curve. Practical applications: From the academic point of view, the results of this work will help to avoid misunderstandings during the study of the grains hydration process, as many hypotheses were reanalyzed and argued. Furthermore, it provides new data, in special for sigmoidal behavior grains, which is very scarce in the literature. From the industrial point of view, this work provides data about the hydration kinetics of several grains, which is very useful for the process design. © 2017 Wiley Periodicals, Inc.