There is scientific evidence that Stevia leaves, commonly used as a sugar substitute, can reduce the risk of obesity, diabetes, hypertension, or cardiovascular diseases. In this study, the moisture sorption isotherms of stevia leaves at 35°C, 45°C, and 55°C were analyzed by the static gravimetric method within a relative humidity range between 0.06 and 0.92. The experimental data obtained exhibits a J‐shaped Type II sorption isotherms. The data were fitted to six mathematical models: Iglesias & Chirife, Lewicki, Oswin, Hasley, GAB, and Khun. GAB model was the one best‐fitted to the isotherms obtained. The monolayer value was between 0.0479 and 0.0589 g water/g dry matter. The isosteric heat of adsorption and Gibbs free energy were obtained at different temperatures using the Clausius–Clapeyron equation. The isosteric heat of adsorption exponentially decreased from 2850 J/g to 2480 J/g as the equilibrium moisture content increased from 0.062 to 0.522 g water/g dry matter. The chemical potential of adsorption increased at high moisture content values. These results suggest an exothermic, spontaneous process. Novelty Impact Statement The importance of studying adsorption isotherms, and its fitting to a mathematical model, allows us to know the potential of the water that influences on the reactions of physical‐chemical deterioration correlated with the stevia leaves stability and quality. The thermodynamic properties derived from moisture adsorption isotherms provide relevant information about the water chemical potential and the energy amount required in moisture adsorption processes, and its relationship with stevia stability in different storage conditions.

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This paper proposes a method to determine bioethanol concentration that uses a pycnometer verified with a high performance liquid chromatography (HPLC) technique; it is a simple tool to determine the density of liquids for getting information about the ethanol concentration. The results showed that the sugar concentration affected the bioethanol concentration. A lower initial sugar concentration of 26.5 g/L generated higher yield of 45.3% sugar to bioethanol and a fractional or relative yield of 88.74%. Significance tests were used to compare the two experimental means, revealing that the pycnometer method and HPLC provide the same bioethanol concentration with joint variances of 2.269, 0.242, and 0.112 for 3 different tests with initial sugar concentrations of 26.486 g/L, 49.043 g/L, and 68.535 g/L, respectively. This study established and developed a methodology to determine bioethanol concentration from coffee mucilage by the proposed method.

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