measurements, respectively, indicating the high reproducibility of the
Fermograph data. These results clearly show the reliability of the
automatic measurements of carbon dioxide emission utilizing the
Fermograph.
A major merit of automated fermentation analysis is the shortening of
measurement intervals to allow the generation of high-resolution
fermentation profiles. In contrast to the manual measurement of multiple
samples, which is labor-intensive and time-consuming, a Fermograph
instrument is able to simultaneously measure carbon dioxide emission of
20 sake mash samples at either 15- or 30-min intervals for 15 or 30 days,
respectively. Furthermore, Fermograph measurements at short and
precise intervals enable the accurate estimation of carbon dioxide
evolution rates, which correspond to ethanol fermentation rates under
the hypoxic conditions of sake mash.
To further evaluate the fermentation profiles generated by the
Fermograph system, sake mash prepared as described above was
inoculated with either strain K7 or X2180 and monitored over a 2-week
period (Fig. 2A–C). A comparison of the time courses of total carbon
dioxide emission (ECO2) showed that the K7 sake mash emitted
approximately two-fold more carbon dioxide than the X2180 sake
mash after 2 weeks of fermentation (7.90±0.04 vs. 4.20±0.02 l,
respectively) (Fig. 2A), demonstrating that K7 is significantly more
efficient at ethanol production under these conditions. The time courses
of carbon dioxide emission velocity (VCO2) provided more detailed
fermentation profiles (Fig. 2B, C). Notably, although the estimated VCO2
of the K7 and X2180 sake mashes was nearly identical during the initial
1.5 days, the fermentation rate of the X2180 sake mash exhibited a
drastic decrease immediately after the peak level of carbon dioxide
production was reached (16.3±0.2 ml/30 min at 2.2 days), while that
of the K7 sake mash reached a higher peak (18.7±0.1 ml/30 min at
3.7 days) and decreased more gradually. Thus, VCO2–T and VCO2–ECO2
plots are useful for identifying the peaks and fluctuations in fermentation
rates which characterize fermentation profiles, including the
kinetics and progression of sake fermentation.