Assessment of the sugars and ethanol development in beer fermentation with FT-IR and multivariate curve resolution models

Fast monitoring of fermentable sugars and ethanol development during the fermentation process is a key point in the final definition of the conformance of the final beer with its defined specifications. In this work six beer fermentation trails were performed according to a factorial design with the two different S. cerevisiae strains (WLP005 and WLP570) and three different fermentation temperatures (19, 21 and 24 °C), all replicated twice. Samples were collected directly from the supernatant every 22 h until day nine and analyzed with Fourier-transform infrared attenuated total reflectance (FT-IR ATR) spectroscopy and a refractometer. Multivariate curve resolution-alternating least squares (MCR-ALS) models were successfully developed to follow the fermentation progress (99.9% of explained variance, 3.5% lack of fit, and standard deviation of the residuals lower than 0.023). The spectral changes of the main components of wort (maltose, maltotriose, fructose, sucrose, dextrins and ethanol) were fully described by using FT-IR and MCR-ALS models, attributing the main changes governing the processes to maltose, maltotriose and ethanol evolutions.