Malt roasting quality control by mid-infrared spectroscopy

In the presented investigation, the chemical composition of malt during roasting is estimated using diffuse reflectance mid-infrared fourier transform (DRIFT-MIR) spectroscopy and multiple linear regressions. Accordingly, the corresponding test setup is presented and evaluated. A total number of sixty-five stop roasting, having temperature range from 140 to 220ºC, and one unroasted sample of 1500 g Avalon malt are performed in an eddy current roaster. Roasted and unroasted malt samples are milled and then analysed. Additionally, analytical standard reference methods are performed for colour, spectral tristimulus L*a*b* - values, colour difference (DE), iron-content, quantitative radical generation and the formation of specific intermediates, such as 5-(hydroxymethyl) furfural (HMF) as well as 3?deoxy?hexosulose (3-DH) and end products of Maillard reaction on all sixty-six samples. Multiple linear regression models were used to predict analysed references based on mid-infrared data, modified with spectral pre-processing for better prediction performance. The obtained results indicate that DRIFT-MIR spectrometry, combined with pre-processing and selection of evaluated wave number areas, is a useful analytical tool for the measurement of quality attributes of malt and therefore, shows potential for application in quality and process control.   Key words: Malt roasting, mid-infrared, optical spectroscopy, process control, EBC, L*a*b*, DE, quality control.