25 Table 1: Headspace Trap Conditions


Headspace System Vial Equilibration Needle


Transfer Line Dry Purge Trap


Extraction Cycles


Gas Chromatograph Column


Oven Injector Inlet Mode


TurboMatrix (40 or 110) HS Trap 80o


120o 140o


C for 20 minutes C


C, 0.25mm id fused silica 7 min


Beer: Low 30o 1 cycle


Table 2: Gas Chromatographic Conditions Clarus 680


Elite-5MS 60m x 0.25mm x 1.0µm or Elite 624 Sil 60m x 0.25mm x 1.4µm 35o


C for 5min, then 6o C/min to 245o


Capillary Split/Splitless, 180o HS Mode


Table 3: Mass Spectrometer Conditions


Mass Spectrometer Scan Range Scan Time


Interscan Delay Source Temp Inlet Line Temp


Clarus SQ 8


35 to 350 amu 0.1 sec 0.06 sec 180o 200o


C C


Table 4: Calibration for the five compounds Component Name Acetaldhyde*


SIM results from Simultaneous Full Scan/SIM Acquisition Signal to Noise Ratio @ 5ng/mL r2


553 to 1


Dimethyl Sulphide** (FS) 7081 to 1 2, 3- Butanedione 2, 3-Pentanedione trans-2-Nonenal


358 to 1 470 to 1 516 to 1


*Acetaldhyde concentration were 8 times higher ** For DMS, the Full Scan data was used for signal to noise and Calibration


industry. For example, it is very important to monitor vicinal diketones (VDK), specifically 2, 3-butanedione (diacetyl) and 2, 3-pentanedione in the beer, because they are known to affect its taste. These components produce a butter-like flavour and are considered detrimental at high levels, especially in lighter style beers.


It is also critical to identify sulphur compounds in beer, such as sulphur dioxide and dimethyl sulphide (DMS). DMS in particular has the taste and aroma of sweet corn, which either comes from not boiling the malted wort long enough, or chilling the wort too slowly, resulting in bacterial contamination. When present in beer at low ppb quantities, sulphur components are considered acceptable, but at higher levels


they give off an unpleasant taste and smell of rotten eggs.


In addition, the monitoring of unsaturated aldehydes like trans 2-nonenal is important, because they are reduced to ethanol by yeast during secondary fermentation. However, oxidation of the finished beer may reverse this process, converting ethanol back to an aldehyde. This is considered a defect, because (t) 2-nonenal in particular has been likened to the taste and aroma of cucumbers and in high concentrations, has been compared with wet cardboard or body odour.


Therefore, with these kinds of demands, plus other relevant testing procedures to ensure the quality of the brewing process,


0.9990 0.9998 0.9992 0.9991 0.9993


range from 5 to 1000 ng/mL C C, Split off Experimental


For this analysis, a headspace trap sample introduction system was utilised which ensures that non-volatile components of the beer, such as sugars, remain in the headspace vial preventing contamination of the analytical system. This reduces maintenance and optimises productivity. In addition, headspace is a component concentration technique, and combined with a trap, allows the focusing of larger volumes of the sample to be analysed, enabling lower detection limits required for many attribute and defect compounds. This concentration step is required to compliment the sensitivity threshold of the skilled beer tasters, who are still a very important aspect of the quality assurance of the brewing process.


A volume of beer is dispensed into a vial and sealed, so the subsequent analysis can be fully automated. A slightly-polar 60m x 0.25 mm x 1.0 µm Elite 5 (5% phenyl-silicone) column was used for the separation. This column provided both sufficient retention to separate the most volatile and early- eluting components and the dynamic range necessary to separate both high level and low level components in the beer.


Sample Preparation and Chromatographic Conditions


5mL of each sample of beer was pipetted and sealed into a standard 22-mL sample vial with an aluminium crimped cap and PTFE lined silicone septum. The instrumental conditions for this analysis are given in Tables 1-3.


Results


A seven-concentration level calibration up to 1000 ng/mL (ppb) was prepared for


C: High 260oC; hold 7 min the following investigations were carried out:


• Quantitation of five VOC compounds: o Acetaldehyde


o 2,3-butanedione (diacetyl) o 2,3-pentandione


o dimethyl sulphide (DMS) o trans (t) 2-nonenal


• Characterisation of flavour components of several types of beers


• Profiling the fermentation process • Analysis of raw materials • Aging studies


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