Enhanced NIR Calibration for Wort Fermentability Using Orthogonal Signal Correction

Abstract

An enhanced method for the calibration of Near Infra Red (NIR) reflectance spectra to wort fermentability is proposed using a signal pre-processing algorithm called orthogonal signal correction (OSC). Pre-processing NIR spectra prior to partial least squares Project to Latent Structures (PLS) regression modelling is becoming commonplace in multivariate calibration. A set of twenty wort samples subjected to a replicated 2 2 factorial design with a centre point and nine production samples were used to construct multivariate prediction models. The experimental design factors were the mash tun saccharification temperature and time used to purposely provide a sample set with significant leverage in the fermentability responses. Calibration PLS models for both wort apparent degree of fermentation (ADF) and final attenuation apparent extract (Final AE) values with and without OSC corrected spectra were compared demonstrating significant improvements in prediction capability with the prior (Q 2 = 0.90 versus Q 2 = 0.28). The OSC algorithm removed almost 60% of the variance in the NIR spectra, which was independent or orthogonal to the fermentability measures. By cleaning up the spectra, the standard errors of prediction (SEP) for ADF and Final AE were improved by 50 and 90%, respectively, illustrating not only the enhancement in calibration but also the aptness for process control applications. Various model validation tests, including an external validation example and random response permutation, verify the validity of the models using OSC. Furthermore, interpretation of the important wavelengths related to wort fermentability is provided and demonstrates that some key wavelengths are related to both carbohydrate overtones as well as nitrogen functional groups. The application of OSC prior to developing calibration models with NIR demonstrates promising results for brewers interested in real time control of wort fermentability.

The application of near-infrared spectroscopy in beer fermentation for online monitoring of critical process parameters and their integration into a novel feedforward control strategy

“…In addition, no reagents are required and therefore no waste products are produced. Also, NIR analysis is multivariate in that a single spectrum contains information about a number of analytes, allowing for several determinations to be made simultaneously (2,(4)(5)(6)8,9). Instrument precision can also be high; however, intensive calibration procedures are required.…”

“…In addition, analysis is not always done in‐house and results are obtained hours, even days, after the samples are initially taken. This limits their potential to be utilized for monitoring purposes or in any type of control strategy aimed at modulating process conditions to help ensure end product consistency . A successful control strategy depends first on reliable and accurate data obtained in a timely enough manner to be able to alter conditions within the process accordingly.…”

The Brewing Industry and the Opportunities for Real-Time Quality Analysis Using Infrared Spectroscopy

“…One of the final stages of brewing is fermentation (Figure 2), where the sugars from malt and solubilized in the wort will be consumed by yeast to produce alcohol. Several studies have shown the potential to assess the fermentability of wort using NIR [63,77,78]. This would be of great benefit to the brewers, as with the data of wort sugars, brewers could confidentially pitch yeast to obtain an optimal fermentation, rather than risking fermentation finishing too soon or too late which is a cost.…”

A Comparative Investigation of the Combined Effects of Pre-Processing, Wavelength Selection, and Regression Methods on Near-Infrared Calibration Model Performance

“…The notations used in this section are as follows: , denotes the raw spectra for the ℎ sample OSC is derived from the ordinary PLS algorithm with the aim of removing bilinear components from which are orthogonal to [16]. The method was applied to enhance NIR calibration of wort fermentability [17]. There are other variants of OSC algorithms proposed in the literature with successful applications therein [18][19][20].…”

“…16 The method was applied to enhance NIR calibration of wort fermentability. 17 There are other variants of OSC algorithms proposed in the literature with successful applications therein. [18][19][20] Extended multiplicative signal correction is an extension of multiplicative signal correction (MSC) by considering wavelength-dependent spectral variations:…”