Monitoring small-scale alcoholic fermentations using a portable FTIR-ATR spectrometer and multivariate analysis

Abstract

Although some wine production processes still rely on post-production evaluation and off-site laboratory analysis, the new winemaking industry is aware of a need for a better knowledge of the process to improve the properties of the final product. Thus, more and more wineries are interested in incorporating quality-by-design (QbD) strategies instead of postproduction testing because of the possibility to early detect deviations in fermentation or any other wine process. This would allow to detect unwanted situations and eventually to ‘readjust’ the process, thus minimizing rejects. 

A strategy consisting on coupling FTIR-ATR spectroscopy and multivariate analysis is here proposed as a fermentation process control strategy. The idea was to develop a portable, rapid, easy-to-use and economic device/tool to monitor fermentation processes and to detect deviations from the normal fermentation conditions (NFC). A portable FTIR-ATR spectrometer was used to monitor small-scale alcoholic fermentations (microvinifications), some of them conducted in NFC and some others intentionally deviated from it. FTIR-ATR measurements were collected during the fermentation process and relative density and content of sugars (glucose and fructose), acetic acid, malic acid and lactic acid were analyzed by traditional methods. 

Multivariate analysis (exploratory methods and linear regression methods) was applied in order to model the whole fermentation process and detect deviations. The prediction of the sugar content in fermenting samples was achieved, demonstrating the possibility to use this portable device to rapidly monitor fermentations and to detect at an early stage slower fermentations, giving the possibility to the winemaker to eventually correct the process and to obtain a good quality product. Moreover, control charts based on multivariate Hotelling T2 and Q statistics were built to detect abnormal deviations. In conclusion, this methodology shows great potential as a fast and simple at-line analysis tool for early detection of fermentation problems. 

Acknowledgment:

The financial support by the Spanish Ministry of Science and Technology (Project AGL2015-70106-R) is acknowledged.