Analysis of Volatile Compounds in the Fermentation of Beer

INTRODUCTION

The chemical analysis of alcoholic beverages is an important step in quality control, being used to monitor flavour profiles across batches, study chemical changes in the product over time, and identify the source of any problems (e.g. off flavours).

The complex flavour of beer is primarily a result of the ingredients used, the brewing method, and conditions during fermentation, and the analysis of beer throughout this process can be invaluable in monitoring fermentation and establishing the point at which problems occur. Being one of the most widely consumed beverages worldwide, rapid and reliable analytical techniques are essential to keep up with demand and production.

Gas or liquid chromatography-mass spectrometry (GC/MS or LC/MS, respectively) are traditionally utilised for quality control in the spirit and beverage industry; however, these techniques can be relatively time-consuming and not necessarily ideal for rapid, high-throughput analysis.

METHOD

Figure 1: Advion expression® CMS with vAPCI heat transfer line.

Figure 2: Schematic of vAPCI/CMS.

Aliquots of the homebrew (1 mL) were collected and analysed 12 hours, 4 days, and 14 days into the fermentation process, in addition to mosaic hop leaves (1 g). The homebrew also contained simcoe and citra hops, which were not analysed.

Each aliquot was sealed in a glass vial and heated to 70oC for 10 minutes. The headspace was drawn directly into the CMS by the Venturi Effect of the vAPCI source for analysis. Samples were analysed in positive ion mode over a range of 30-300 m/z, with a scan time of 400 ms.

RESULTS AND DISCUSSION

Figure 3: Mass spectra of homebrew headspace at (A) 12 hours, (B) 4 days, and (C) 14 days) into fermentation.

There were distinct changes in the overall volatile profile, notably the gradual increase in the m/z 93 ion, likely the protonated ethanol dimer (Figure 3). The concentration of this ion plateaus at the 4 day timepoint, demonstrating fermentation primarily occurred in the first few days.

Figure 4: Mass spectrum of mosaic hops, added 4 days into fermentation.

The headspace of mosaic hops used in in this homebrew were also analysed. The hops mass spectrum (Figure 4) was dominated by ions at m/z 81, 137 and 273, all of which are common ions associated with terpenes, a class of compounds responsible for many of the aromas and flavours of hops. Many of these compounds are of the same molecular weights and thus further analysis would be required to differentiate and identify these components. Components derived from hops are readily detected in the beer aliquots, particularly after the 4 day timepoint, when additional hops were added.

CONCLUSIONS

This study demonstrates the use of the Advion expression® CMS with vAPCI for the analysis of volatile compounds from the headspace of home-brew beer and hops. The Venturi-assisted interface of the instrument enabled rapid sampling of volatiles, allowing the changing volatile profile of the homebrew to be observed throughout the fermentation process. This simple method would be suitable for fast quality control during alcoholic beverage production.