This research aimed to assess the effect of the initial condition of the pineapple stubble waste on the solid-fuel properties of the hydrochar obtained by the hydrothermal carbonization process. Pineapple stubble was subjected to hydrothermal carbonization in a high-pressure reactor at 200 °C for 1 h, using a 1:20 dry-basis biomass-to-water ratio. The resulting hydrochar was filtered under vacuum and dried at 85 °C for 12 h. A randomized complete block design evaluated the influence of three key variables: the initial moisture content of the biomass (original moisture, 50% of its initial moisture, and completely dried biomass), the state of the biomass (freshly collected and cut several days before), and particle size (processed using four different mills). Hydrochar characterization included elemental analysis, higher heating value (HHV) determination, and calculations of hydrochar and energy yields. The results showed no significant differences in hydrochar production or energy yield across the analyzed variables, with average yields of 47% and 60%, respectively. However, hydrochars from fresh pineapple stubble residues exhibited significantly higher HHVs, with an average of 20.6 MJ/kg, classifying them as high-calorific-value biomass. In conclusion, these findings suggest that the overall energy efficiency of the hydrothermal carbonization process, as measured by energy yield, remains consistent across the range of pre-treatment conditions investigated, providing key evidence for the successful scaling of the process in industrial applications. These findings also highlight the potential of hydrochar from pineapple stubble as a solid biofuel, supporting its role in renewable energy diversification strategies.