A new experimental setup that makes possible in-situ determinations of the population density function of the methane hydrate particles during its crystallization in a pressurized reactor is used. Thanks to this equipment, new results can be obtained, in particular concerning the granular aspects of the crystallization processes and the influence of the stirring rate. These results are discussed in the framework of a model including gas absorption, primary and secondary nucleation, crystal growth, agglomeration, and breakage. From this discussion, the relevant processes and parameters of methane hydrate crystallization can be determined and quantified.