Monitoring and evaluation of alcoholic fermentation processes using a chemocapacitor sensor array

Abstract

The alcoholic fermentation of Savatiano must variety was initiated under laboratory conditions and monitored daily with a gas sensor array without any pre-treatment steps. The sensor array consisted of eight interdigitated chemocapacitors (IDCs) coated with specific polymers. Two batches of fermented must were tested and also subjected daily to standard chemical analysis. The chemical composition of the two fermenting musts differed from day one of laboratory monitoring (due to different storage conditions of the musts) and due to a deliberate increase of the acetic acid content of one of the musts, during the course of the process, in an effort to spoil the fermenting medium. Sensor array responses to the headspace of the fermenting medium were compared with those obtained either for pure or contaminated samples with controlled concentrations of standard ethanol solutions of impurities. Results of data processing with Principal Component Analysis (PCA), demonstrate that this sensing system could discriminate between a normal and a potential spoiled grape must fermentation process, so this gas sensing system could be potentially applied during wine production as an auxiliary qualitative control instrument.

Figure 1.

Experimental set up for the interface of the volatile headspace of the examined fermented medium with the sensor array.

Figure 2.

Optical micrograph of the IDE dimensions.

Figure 3.

The evolution for the two different fermentation processes over time after daily chemical analysis in terms of sugar consumption and ethanol production.

Figure 4.

Volatile acidity propagation during the two fermentation processes. The results obtained by standard chemical analysis with steam distillation and titrimetry.

Figure 5.

Typical example of dynamic responses of two sensors of the sensor array upon exposure to reference and fermented must. (Sample of fermented must: Must 1 fermentation process-Day 6). Also zoom in PS-coated sensor response is shown (insert graph).

Figure 6.

Differential equilibrium responses of the relative hydrophobic P(iBMA)-coated sensor and the relative hydrophilic PHEMA-coated sensor over fermentation duration.

Figure 7.

Equilibrium responses of a relative hydrophobic polymer-coated sensor upon exposure to the headspace of pure ethanol solutions in comparison with data of fermentations.

Figure 8.

Equilibrium responses of a relative hydrophilic polymer-coated sensor upon exposure to the headspace of pure ethanol solutions in comparison with data of fermentations.

Figure 9.

PCA analysis of the sensor array. Data processed: equilibrium responses during the fermentation progress.