Methanol-to-water (CH₃OH/H₂O) column density ratios reported in the literature for a wide range of clouds, YSOs, and Solar System comets (see Sect. 4.1 for references). The values for molecular clouds, LYSOs, and MYSOs reflect the ice composition, whereas the ratios were measured in the gas-phase for protoplanetary disks and comets. Open symbols indicate protoplanetary disks in which the upper or lower limit on the methanol-to-water column density ratio was estimated by combining measurements taken at different wavelength ranges. Upward triangles for the HD 100546 and the IRS 48 disks indicate lower limits, whereas downward triangles for DG Tau A and HL Tau indicate upper limits. HL Tau values were obtained by dividing the 3σ upper limit on the $N_{{\text{CH}}_3\text{OH}}$ for the three assumed excitation temperatures in Table 2 by the water column density measured by Facchini et al. (2024).