Cerevisia : Belgian journal of brewing and biotechnology

In situ Optical Rotation Measurement for On-Line Monitoring of Brewery Fermentations

JORGE HUERTA, JORGE HUERTA — Wed, 01 Jun 2022 00:00:00 +0000

Fermentation is an important part of brewing with the potential for high variability. Monitoring fermentation progress on-line in real time improves a brewer’s ability to control the process and reduce variability. Several techniques have been standardized by ASBQ to measure ethanol content, but all of them are off-line measurements. Our objective was to evaluate a novel, optical rotation instrument that uses a photoelastic modulator to measure sugar consumption on-line during fermentation. The optical system was developed using commercial, low-cost components. A semiconductor laser beam was polarized and modulated at 50 kHz with a photoelastic modulator. The light was then passed through a sample cell followed by another polarizer acting as an analyzer. Transmitted light was collected using a silicon detector and its electric signal was filtered with a lock-in amplifier. Different sucrose solutions at concentrations from 0.01 to 30% (w/v) were used to calibrate the instrument and determine its sensitivity, linearity, and stability. Continuous sampling of a fermentation was accomplished by circulating fermenting wort via a peristaltic pump to the optical cell of the instrument. To verify and correlate results, additional samples were taken off-line to measure ethanol content by gas chromatography and specific gravity using a precision density meter. A significant linear correlation was found between on-line optical rotation measurements and off-line ethanol and density measurements, thus confirming the feasibility of optical rotation as an in-situ measurement technique for monitoring fermentation progress.

Comparison of Methods for Assessing Colloidal Stability of Beer

KARL J. SIEBERT, P. Y. Lynn — Wed, 01 Jun 2022 00:00:00 +0000

Numerous methods for assessing colloidal stability of beer have been developed. Some of these, such as forcing tests, are mainly used to ensure that beer has been adequately chillproofed; unfortunately, the results are often only available after the beer has left the brewery. The Chapon alcohol cooling test is much faster but requires special equipment and is ill-suited for use as a routine procedure. Other tests, such as the saturated ammonium sulfate precipitation limit (SASPL) and the sensitive (or haze-active) protein test (based on haze induction with tannic acid, followed by turbidimetry) focus on the protein side of colloidal stability and are mainly used in research studies. It was of interest to compare results of these tests on beer treated with different amounts of silicas of different types and particle sizes. Unchillproofed lager beer of a single brand from a single brewery was treated with a number of different silicas, each at three different addition rates (150, 300, and 1,000 mg/L). Each of the resulting samples was subjected to a battery of analytical methods that are often used to evaluate colloidal stability: SASPL, an elevated temperature forcing test, the Chapon alcohol cooling test, and the haze-active (HA) protein test. The HA protein and forcing tests were slightly more precise (lower coefficients of variation) than were the SASPL and Chapon tests. The results obtained with the different methods showed similar, but not identical, patterns with the different silicas; with each method, the three treatment levels with each silica were readily distinguished from each other and from an untreated control. The silicas of different sizes produced generally similar results. The largest particles had slightly lower SASPL and slightly higher HA protein values (both indicating less stability), but in the forcing test, the differences were negligible, with no apparent pattern. The results of the forcing, alcohol-cooling, and HA protein tests showed comparable patterns within the sample set and essentially linear relationships with each other. The SASPL test, on the other hand, showed differences between the samples, but in a different pattern than the other assays. Its relationships to the other methods were distinctly curved. Since the forcing test is the closest to normal practice, it should be the most relevant result. The alcohol-cooling test and the HA protein results were in good agreement with the forcing test, demonstrating their utility in predicting colloidal stability, at least with a single beer brand. As a result, either test should be useful for making comparisons of silica efficacy. The results call into question the utility of the SASPL test for assessing beer haze potential. The short analysis time needed for the HA protein test would permit product testing prior to packaging.

Measurement of Nonenal Potential by Solid-Phase Microextraction (SPME)

Alexis Bolívar, Julia Franquíz, Mónica Gasparri, and CARSTEN ZUFALL — Wed, 31 Aug 2022 00:00:00 +0000

The Nonenal Potential is considered an indicator for the staling characteristics of a sample. Malt extracts, worts, and beers are among the commonly analyzed materials. Its relatively high nonenal figures have made Nonenal Potential analyses easier to carry out than measurements of the free aldehydes. The often-difficult interpretation of free aldehyde concentrations as a measure of flavor stability have also contributed to the widespread use of Nonenal Potential analyses. Since the original presentation of the concept in 1990, many variations of Nonenal Potential measurement have been published, both in terms of variations of the sample digestion procedure as well as different approaches in nonenal analysis itself. Current-published methods include a variety of time-consuming and expensive steps in sample preparation, such as column chromatography and derivatization, which also may decrease reproducibility. To overcome the above-mentioned difficulties, a novel solid-phase microextraction analysis method for 2(E)-nonenal without derivatization or other pretreatment steps has been developed. The activation of 2(E)-nonenal precursors takes place in a headspace vial with 10 mL of acidified sample, pH 4.00, at 100°C for 2 h. The vial is refrigerated at 0°C and opened, Na₂SO₄ added with a magnetic agitator, and sealed. An SPME fiber is placed in the headspace solution for 1 h at 70°C. The 2(E)-nonenal adsorbed on the fiber is analyzed by CG/MS in SIM mode. Besides eliminating derivatization efforts and cost, the new method requires significantly less time compared with previously published ones. The new method has been validated testing linearity, accuracy, precision, specificity/selectivity, range, and ruggedness/reproducibility, as well as detection limit.