Fig. 2

Comparison of differential pressure sensor (∆p sensor) and non-dispersive infrared CO₂ sensor (NDIR CO₂ sensor) for CTR measurement. CTR over time determined with ∆p sensor (red) (as described by Anderlei et al. [17] and NDIR CO₂ sensor (green). For comparison of both methods, a ∆p sensor was included in the measurement setup as illustrated in Additional file 2 B. The open vent hole was replaced by a switchable outlet valve, to allow for gas tightness. Data points are presented as duplicate measurements in two individual shake flasks (square and triangle). The solid line connects the average of these two data points. A Saccharomyces cerevisiae (S. cerevisiae) cultivation in yeast extract peptone medium (YEP-medium) containing 20 g/L glucose. Operation conditions: shaking frequency n = 200 rpm, shaking diameter d₀ = 50 mm, liquid filling volume V_L = 25 mL, 250 mL shake flask, temperature T = 30 °C, measurement time t_meas = 6 min; B Gluconobacter oxydans (G. oxydans) in Jülich-medium containing 80 g/L mannitol. Operation conditions: n = 350 rpm, d₀ = 50 mm, V_L = 10 mL, 250 mL shake flask, T = 30 °C, t_meas = 6 min