Monitoring of alcoholic fermentation: development of an applicable in-line system

The alcoholic fermentation is an important phase of the winemaking process. Besides the production of ethanol, it leads to the formation of several secondary metabolites having a significant impact on the characteristics of the wine. A careful management of alcoholic fermentation ensures that it takes place over a sufficiently long time allowing the release of varietal aromas and the formation of fermentative aromas. Stuck fermentation should be prevented as it can impoverish the wine as well as it can lead to the appearance of undesired aromas. In general, in-line monitoring of a process, which can be achieved thanks to the use of sensors, allows for rapid intervention, thus avoiding the onset of defects. Nowadays, different types of sensors are used for the entire wine production chain, from the monitoring of grape ripening to the wine bottling (Thanasi et al., 2022). However, the use of sensors can be implemented if their cost is competitive, thus becoming a sustainable tool for a winery. The objective of the research was the development of a low-cost prototype to monitor the fermentation process using VIS/NIR optical sensors. The prototype is equipped with sensors that operate in the wavelength range between 340 and 1050 nm, which are easily available on the market. Parts of the prototype were made via 3D printing. The prototype was tested for monitoring fermentation at (i) laboratory (microvinifications) and (ii) industrial scales. For the latter, 3 types of must were considered (white, red and rosé) obtained from three different batches of grapes for a total of 9 fermentation processes monitored. Samples were taken daily for the determination of sugar concentration, measured by enzymatic analysis, and for optical analysis. The results obtained by enzymatic analysis were used as reference parameters to develop predictive models through chemometric analysis, using the partial least squares (PLS) regression technique. The models developed on a laboratory scale (internally validated through cross-validation) have demonstrated the ability of the device to capture, directly and/or indirectly, the chemical information relating to the sugar concentration of the analyzed must samples. The first results regarding the monitoring of fermentation on an industrial scale seem to indicate the existence of a good correlation between the concentration of sugars determined by optical and enzymatic analysis, similar to what is observed on a laboratory scale. Therefore, the prototype laid the basis for the development of a valid and economical instrument which, together with temperature and carbon dioxide sensors, already widely used, would optimize the monitoring and fermentation processes.