When formulating materials containing an hydraulic binder and plant particles, the setting of the binder may be slowed or prevented by the compounds extracted from the plant. In this article, a methodology is fixed to analyse three types of hemp shiv and to study the variability of the composition of extractives and their influence on the hydration of cement. Isothermal calorimetric measurements have shown that one type of shiv caused a greater delay in the setting of the cement. Analysis of free compounds extracted from the plant has shown that this shiv has a higher content of extractives, and in particular, of sugar. By using the same quantities of standard sugars, it was found that the measured sugar content could not, in and of itself, account for the delay in hydration measured in the presence of shiv. Other extracted molecules, such as phenolic compounds, also play a part in the hydration of the cement.