The hydration process is an important step during grain industrialization. It is needed prior to germination, cooking, fermentation and extraction of components. Being a slow and a discontinuous unit operation, the hydration must be better understood and studied. Different descriptions are available in the literature supposing how size, shape, colour, species and families affects the hydration behaviour of pulses and cereals. However, most of them were not demonstrated, doubting its validity. In order to evaluate these hypotheses, 22 grains in a broad range of varieties were hydrated at 25±1ºC, evaluating their hydration kinetics. Some of them were studied for the very first time: Caballero beans, Dark red kidney beans, Egypcian kidney beans, Canary beans, Green lentils, Pink kidney beans, Fava beans, Ñuña beans, Black kidney beans and Panamito beans. Both downward concave shape and sigmoidal shape behaviours were obtained, being fit to appropriate models. Notably, the first 5 of the new grains studied list above were identified as sigmoidal, which is the less studied behaviour in literature due to its recent characterization. Among all of the 22 grains, sigmoidal was observed in a total of 10. Comparisons were made among grains from the same species, from different and similar shapes, sizes and colours, and the results allowed us to dismiss the following hypotheses: darker grains hydrated slower than lighter grains; grains with sigmoidal behaviour hydrate slower than those with downward concave shape behaviour; the smaller the grain is, the faster the hydration will be. So, it was concluded that the hydration process is complex, being influenced by several intrinsic factors. In fact, isolating one of them is a difficult task.