Modem instrumental analytical techniques play an important role in the brewing industry today. They are extensively used for both a quality control/quality assurance function and for research purposes. At all stages of the production process, from the assessment of raw materials, through the brewing process, fermentation, maturation, blending of finished beer, packaging and shelf life studies instrumental analytical techniques provide critical data which allow the brewer to understand and keep his process in control Research is ongoing to develop new, more efficient, more sensitive and more selective analytical techniques to achieve a greater understanding of the processes described above and to provide better quality beer at low cost. This thesis describes some such analytical methods which were developed as a result of specific practical needs which arose during normal brewing practice over a number of years Roasted barley is a most significant ingredient of Guinness Brewing Worldwide stout products. A novel analytical method is presented for the analysis of the volatile flavour constituents of roasted barley which is rapid and requires little sample preparation. Secondary coolants are widely used in brewery production plants. A sensitive method was developed for the detection of possible coolant contamination in beer. The method was based on the addition of a fluorescent dye to the coolant in so that in the event of leakage into beer this contamination could be detected by a simple fluorescence measurement of beer. The development of a gas chromatographic method for the analysis of propylene glycol in beer is presented Propylene glycol is a major constituent of the secondary coolant used at the Guinness Ireland Group, Dublin site It is also naturally present in beer. Two analytical methods are described for the analysis for styrene in beers Styrene is present due to the ability of some yeast strains to decarboxylate phenolic acids present in wort Such yeasts are classified as Pof“ yeasts 1 e produce phenolicoff- flavour Methods are described for the classification of phenollc-off-flavour (Pof1) producing yeast strains Formation of styrene during a fermentation was investigated. Studies into the kinetics of styrene production were also carried out.