This study evaluates the effect of ten organic additives belonging to the classes of carbohydrates and sulfonates on the microstructure of portlandite crystals during CaO hydration. Calcium hydroxide modified with selected additives was prepared and characterised in terms of crystal size and habit, platelets abundance, crystallinity, specific surface area, particle size distribution, calcium concentration and organics in solution, using XRD, SEM, N2 absorption/BET, laser diffraction, ICP-OES and HPLC-MS. The results suggest that the microstructure of portlandite is altered by the presence of carbohydrates and sulfonates, mostly showing higher platelets abundance, smaller crystallite size, and higher specific surface area. The presence of hydroxyl-rich carbohydrates induced more marked effects compared to sulfonates. These results show that it is possible to tailor the properties of lime to specific applications. Consequently, this study can impact the conservation and the construction industry by enabling the development of novel binders for modern construction with optimal properties, and more broadly fields such as the synthesis of precipitated calcium carbonate and the design of CO2 sorbents, all of which will have the added value of reducing the global anthropogenic CO2 emissions.