This paper presents a rapid less than 2 min and low-cost method involving the use of alkali solution to capture the acidic gasses from a biogas, thereby providing an estimate of the percentage of non-acidic gasses. Such a method was mentioned in the literature but never fully described or optimized. After sampling an aliquot of gas from bioprocess, gas was injected in a sealed flask with a 3 M NaOH solution, and after equilibrium was obtained, the non-acidic gas volume was measured. The method was first calibrated with certified gasses with an accuracy observed between 98 and 105%. Regarding the validation step, certified standard gas mixtures and nine biogas-laboratory batch reactors were used, the overall accuracy reported was 103 + 3%. This rapid and low-cost method may either be used in laboratory conditions as a quick and low cost alternative to standard analysis equipment or in addition as a routine field control method used on full-scale plants.