In line monitoring of red wine fermentations using ir spectrospcopy

There has been a shift in modern industry to implement non-destructive and non-invasive process monitoring techniques (Helmdach et al., 2013). This is primarily to ensure that process conditions are maintained at optimal set points, thus improving consistency, efficiency, and control. Implementation of infrared technology and chemometrics in the wine industry has been extensively studied and has been found to be a suitable method of process monitoring, especially when considered in the context of phenolic extraction. However, these studies have conducted spectroscopic analysis off-line and with highly clarified samples (Aleixandre-Tudo et al., 2018; Cavaglia et al., 2020). For the technology to be more applicable to a real life scenario, a shift towards in-line monitoring must be made. The ultimate aim of this study was the development of an automated sampling and analysis system. This system would allow spectroscopic and chemometric technology to become more commonly in commercial cellars and for precision monitoring of phenolic extraction. May challenges exist when sampling directly from a fermentation tank and these can include high levels of turbidity, pipe blockages, exposure to oxygen, and ensuring that a sample is representative of the contents of the fermentation vessel. Turbidity, in particular, is a concern when utilizing spectroscopic methods as the suspended solids may interfere with the trajectory of the radiation, resulting in abnormal spectra and, therefore, inaccurate measurements. A prototype system making use of a series of filter screens was developed and prototyped to determine whether automated sampling and analysis would be possible in a cellar with multiple tanks and a single instrument. Automation software was developed to initiate the IR scanning and the subsequent analysis of the sample, displaying the results for tannin content, anthocyanin and polymeric pigment content, total phenolic index and colour density graphically for the user or winemaker. In addition to this, chemometric models were built to account for the effect of suspended solids in a fermenting sample. The system, as a whole, showed promise with samples being successfully drawn from the tanks and analysed. Lastly, statistical analysis showed that the chemometric models were robust, accurate and suitable for the intended application.

Authors: Kiera Nareece Lambrecht – Stellenbosch University, South African Grape and Wine Research Institute (SAGWRI), Department of Viticulture and Oenology,Dr José Aleixandre-Tudo, Universitat Politecnica de Valencia, Instituto de Ingenieria de Alimentos para el Desarrollo (IIAD), Departamento de Tecnología de Alimentos and Stellenbosch University, South African Grape and Wine Research Institute (SAGWRI), Department of Viticulture and Oenology  Prof Wessel Du Toit, Stellenbosch University, South African Grape and Wine Research (SAGWRI) Institute, Department of Viticulture and Oenology 

Email: kieranareece@sun.ac.za

Keywords: in-line monitoring, process control, spectroscopy, chemometrics

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