Beer, as manufactured, is not at chemical equilibrium and undergoes complex chemical reactions during storage which can lead to undesirable changes in the sensory characteristics of beer. Since beer contains more than 600 volatile compounds, beer flavour change is a complex field of research and the dependable prediction of shelf life remains a top research priority. Chapter 1 places the work described in this thesis into this context. Chapters 2 and 3 provide details of the experimental methods used and their development, respectively, to evaluate flavour stability. The methods used and developed include: (i) the determination of one of the major antioxidants present in beer, sulphur dioxide (SO2), via distillation; (ii) a solid phase micro extraction (SPME)-GC-MS method with on fibre derivatization as a reliable detection method for aldehydes related to off flavours perceived in aged beer; (iii) measurement of the oxidative stability using electron paramagnetic resonance (EPR) spectroscopy. Chapter 4 describes oxidative stability measurements via EPR spectroscopy for three different lager-style beer qualities pre- and post-filtration. The trial included a large scale Kieselguhr frame filter, and two pilot-scale membrane filtration system. The results illustrate how EPR spectroscopy is sensitive to metal ion pick-up from traditional filter media and oxidative stability measures were evaluated versus oxygen pick up during filtration and sulphur dioxide content of the beer samples. The effect of a brewhouse addition of gallotannins on the flavour stability of a lager-style beer was investigated in Chapter 5. Pilot scale (16 hl) and large scale production line (1500 hl) experiments with gallotannins additions in the Brewhouse were performed. The effects of the different additions were monitored at key points of the production process and through to the final beer. Despite showing significant improvements in the pilot scale wort samples, the results for the related packed beer samples did not show clear flavour stability improvements. For the production-scale trials, only a very limited effect of improved flavour stability could be observed. In Chapter 6 a factorial experimental design was adopted to probe the interactions between seven factors known to impact on beer flavour stability. Chemical additions were made to a bright beer prior to bottling, to vary the following factors: total in pack oxygen, SO2, total iron, iso-α-acid and α-acid content, (+)-catechin and glutathione. Increased SO2 concentrations had the largest impact across the entire design space, resulting in reduced radical formation, staling aldehyde concentrations and improved sensory scores. The impacts of increased TIPO levels were rather limited. In contrast, a significant impact regarding the oxidative stability could be observed for increasing Fe concentration, highlighting the significance of pro-oxidative effects of transition metals.

The bitterness of beer remains one of its most important flavour attribute. However, complexity surrounding bitterness perception alone represents a significant challenge in its understanding, in addition to other factors relating to production processes and raw materials used in making beer. The aim of this research was to better understand beer bitterness in terms of its intensity and quality, and how hopping technology (e.g. quantity and time of hop addition during the brewing process), hop aroma and variety may effect perceived bitterness intensity and quality. This project combined both analytical and sensorial analysis, and used statistical techniques to identify the key compounds driving bitterness perception. Analytical techniques were employed to quantify bitterness-contributing compounds and analytical bitterness units in beers alongside descriptive analysis of perceived sensory bitterness. Perceived sensory bitterness (both qualitative and quantitative) was assessed using a purpose developed list of well-defined bitterness attributes, to aid the characterisation of bitterness quality in beers. The impact of cross-modal flavour interactions on the perception of beer bitterness intensity and qualities was also investigated at varying analytical bitterness levels. Lastly, the effect of hop variety, and how this significant raw material affects perceived bitterness quality was also investigated using three distinctively different hop varieties (Hersbrucker, East Kent Goldings and Zeus). Results revealed a significant impact of the analytical profiles of beers, derived from the type of hop products and hopping technology adopted in beer production, on the perceived bitterness quality of beer. In general, beers high in hop acid compounds and polyphenols were, as expected, perceived to be higher in bitterness intensity. The results further showed that bitterness intensity also played a role in the perception of bitterness quality i.e. whether the beer was ‘harsh’, ‘lingering’ or ‘round’. However, beers high in these compounds were not always of ‘negative’ bitterness quality, and correspondingly lower amounts of these compounds did not always result in ‘positive’ bitterness qualities in beer. Results on the impact of cross-modal flavour interactions showed that hop aroma plays a crucial role in beer bitterness perception, and can modify the perception of bitterness intensity and quality as well as temporal profiles of bitterness in beer depending on analytical bitterness levels. The investigation into the impact of hop variety on perceived bitterness quality revealed hop-derived bitterness profiles relating to individual hop varieties, and further suggests that careful selection of the hop variety used for brewing is important for controlling perceived bitterness quality. This research provides a comprehensive interdisciplinary approach to understanding perceived beer bitterness and its associated qualities, with findings suggesting that besides bitterness intensity, the quality and overall impression of bitterness as perceived by consumers are significantly influenced by raw materials, production processes and other factors such as aroma which might be overlooked by brewers - but are likely to be significant for consumer preference and the success of a brand.

Very High Gravity fermentations are an increasingly attractive proposition within the brewing industry as a means of energy saving and optimising process efficiency. However, the use of very high gravity ( > 20°P) wort is associated with a range of biological stress factors. Ethanoic and osmotic stresses have been widely analysed along with oxidative stress in relation to propagation and early stage fermentation. The aim of this research was to investigate the impact of wort gravity on oxidative stress, and understand how this affects the plasma membrane at VHG. Finally the effect altered ergosterol content was analysed. The characteristics of Saccharomyces pastorianus strains were assessed for their ability to withstand the increased pressures of VHG (22°P) fermentations. VHG fermentations showed increase ethanol production at the expense of fermentation length, and increased ethanol production during VHG fermentations was offset by an increase in fermentation length. All fermentations were observed to accumulate ROS and increased antioxidant levels, with levels being furtherelevated in the VHG environment. Further analysis of S. pastorianus strains indicated that the levels of oxidative stress observed in fermentation had a negative effect on membrane fluidity and increased damage of the plasma membrane was observed. Analysis of ergosterol enriched yeast indicated that although fermentation rate was increased, a trade off with alcohol and biomass production was observed. Furthermore in response to oxidative stress, ergosterol enriched yeast showed reduced tolerance, decreased membrane fluidity and increased membrane damage. This work will give further insight into the response of lager yeast to oxidative stress present during VHG fermentations.

The flavor, quality and composition of market brick cheese varies greatly. Its moisture content often ranges from 37 to 43 per cent. The flavor may be similar to Limburger or it may even resemble that of Cheddar. Such a great variation in a specific food product tends toward disappointment for the consumer. It is believed that a more uniform standard of quality for this product is needed to materially increase its consumption. Therefore, a detailed study of some of the factors involved in the manufacture of brick cheese may help to improve the quality and aid in determining a satisfactory standard.

Importance of problem: Ice Milk is not a new product in the ice cream industry. Rather it is one that has gained only little popularity, except in the preparation of "malts" and "milk shakes"; however, within the last decade the gallonage of ice milk produced has more than doubled. Ice milk has been relatively unimportant because of the difficulty of obtaining a product with acceptable quality. In recent years progressive ice milk manufacturers and research workers have discovered new ingredients and processing procedure that seem to produce favorable results. This low-fat product has several merits that justify its recent popularity, such as low cost to the consumer, high nutritional value, an additional outlet for serum solids, and it is an attractive product to those individuals who may be diet conscious. Ice milk differs from regular ice cream in that it contains less butterfat and more solids-not-fat. Frequently when the fat content is decreased there is a tendency for the product to become coarse. In order to correct this coarseness more milk-solids-not-fat are added to the mix which often effects the flavor of the ice milk. Also with an excessive increase of serum solids in the mix there is danger of sandiness developing in the product during storage. Purpose of problem: The purpose of this experiment is to determine a formula and processing procedure that will yield a frozen ice milk product with desirable flavor, good body and texture qualities, and freedom from sandiness after reasonable storage. By the proper balance and use of ingredients and modern processing and freezing methods it is hoped that the quality goal will be reached and prove beneficial to the industry.

Importance of project: In recent years many antibiotics have come to the foreground as a treatment for mastitis. Aureomycin is one of the more recent antibiotics that has been used for this purpose. Aureomycin has been reported to be successful in curing some types of mastitis, but milk produced by cows that have been treated with Aureomycin does not act normal in the cheese manufacturing process. The most noticeable effect in milk from cows treated with Aureomycin has been slow or complete cessation of acid production by bacteria in cultured dairy products; this has been especially true in the cheese manufacturing process. In the even of slow acid production, or complete cessation of acid production, the cheese produced is either of lower quality than would normally be exected, or the entire vat of cheese may be lost. In either case there is a definite advers effect on the dairy industry. Purpose of investigation: The purpose of this problem is to determine the percentage of Aureomycin necessary in milk to cause slow or complete cessation of acid production in the cheese manufacturing process, and to find a chemical or heat treatment that can be used to inactivate the aureomycin so that there will be no harmful effect in milk used to manufacture cheese.

Deposition of amorphous silica (SiO2) and calcium oxalate (CaOx) on the calandria tubes of juice evaporators cause serious processing problems in Australian cane sugar mills. The removal of these deposits by mechanical and chemical means is a timeconsuming and costly experience. The cost of downtime and chemical cleaning can be several million dollars per year for the Australian sugar industry. The interactions between CaOx and SiO2 have not been investigated previously because conventional studies only address fouling by individual components. The present work evaluates their interactions using two experimental approaches: batch tests for assessing kinetic and thermodynamic behaviour, and fouling-loop experiments for examining composite fouling behaviour under different operating conditions. The above two approaches were employed both in the absence and in the presence of sugar to elucidate the effect of sugar on composite fouling mechanisms and to determine the controlling species responsible for composite fouling. The composite fouling experiments were performed in a novel closed-loop circulation system simulating the effect of feed composition of successive stages of evaporation cycle in a single run. In addition, the fouling-loop system was operated in a constant composition mode to study the effects of thermal hydraulic conditions on composite fouling. The combined information obtained from both the batch and fouling-loop tests in this study offer a unique insight into the mechanisms of composite fouling of CaOx and SiO2. Some of the highlights of the obtained results are as follows: ??? Identification of a complex interactive process in calcium oxalate monohydrate ??? silica (COM-SiO2) systems by investigation of the kinetics and thermodynamics of COM-SiO2 coprecipitation in water and sugar solutions, and an understanding of the mechanisms of these interactions; ??? Development of a novel fouling-loop system, which is simple, efficient and cost effective for the study of the effect of juice composition on scale formation in various stages of juice evaporation; ??? Elucidation of composite fouling mechanisms, e.g., a feed composition dependent fouling mechanism is proposed; ??? Isolation and verification of the existence of certain species in composite deposits, which is known to be thermodynamically unstable. In other words, it is established that calcium oxalate trihydrate is stable under certain conditions; ??? Evaluation of the role of thermal hydraulic operating parameters in determining the characteristics of subcooled flow boiling heat transfer and in determining the strength of the composite deposit; ??? Development and validation of an empirical model to predict the subcooled flow boiling heat transfer coefficients in water and sugar solutions; ??? Development of an analytical model incorporating the effects of operating parameters for COM and SiO2 composite fouling in sugar solutions. This model predicted the experimental data better than available models. Results of this work are significant, not only because they have made a valuable contribution to advance the fundamental understanding of heat exchanger fouling, but also because they may play a key role in the development of scale control and removal strategies to minimize the composite fouling in Australian sugar mill evaporators. For example it was found that, in order to effectively minimize the rate of composite fouling and reduce the scale tenacity, it would be necessary to control thermal hydraulic operating conditions, especially the fluid velocity, and to adjust the initial CaOx/SiO2 supersaturation ratio to the optimum value. To achieve the optimal CaOx/SiO2 ratio, certain device can be developed to sequentially measure oxalic acid and SiO2 concentrations in juice so that the correct proportions of chemicals can be added. Model simulations of the composite fouling rate may also effectively and economically provide comparative and relevant information essential for process optimisation and evaporator design

Unlike other fibres, wool felts readily when agitated in the presence of water. For this reason, only the minimum necessary quantity of water is used when the garments are drycleaned. However, wool fibres are often deliberately felted to obtain a warm bulky handle by controlled addition of water to the solvent. This process is known as solvent milling and recently, it has become a popular alternative to the traditional milling in water alone. Although the factors which influence milling in solvent are known, the relationships between them are not well defined. A comprehensive study of the relationship between water distribution and milling shrinkage during agitation of wool in perchloroethylene has been carried out in this thesis. The Karl Fischer method of determination was used throughout to establish the distribution of water between the wool fibre and the solvent liquor. The emphasis was placed on practical production variables. The role of surfactant in affecting milling shrinkage through its effect on the transport of water to the fibre from the solvent was examined. The ability of a suitable surfactant in promoting even and rapid sorption of water by the fibre was related to the colloidal properties of the milling liquor.

Thesis (M. Arch.)--University of Hong Kong, 1994. / Includes special report study entitled: Technology of glass and glass constructions. Includes bibliographical references.

During the past two decades several novel spoilage micro-organisms have emerged. Raw materials and products have been contaminated in increasing numbers of spoilage incidents causing widespread problems within the juice and beverage industry. This study investigates two such spoilage micro-organisms, A licyclobacillus acidoterrestris and Propionibacterium cyclohexanicum, both isolated from pasteurised contaminated fruit juice. A variety of media were tested to determine which supported optimal growth of A. acidoterrestris with Orange Serum Agar providing consistently high plate counts. The presence of A. acidoterrestris in raw materials and shelf stable products was monitored and the effects on its growth and survival of temperature, headspace and movement of containers during storage were investigated. The survival of P. cyclohexanicum after pasteurisation was assessed and growth determined at a variety of temperatures. The survival of each bacterium was investigated in different fruit juices, when challenged by the preservatives sodium benzoate and potassium sorbate and the bacteriocin nisin and when grown in the same juice container and co-cultured on the same solid medium. 17% of samples tested were contaminated by A. acidoterrestris; however P. cyclohexanicum was not isolated from any sample. P. cyclohexanicum survived 10 minutes at temperatures of 4°C to 95°C and grew in orange, tomato and pineapple juice while A. acidoterrestris grew in all juices tested. A. acidoterrestris was inhibited by sodium benzoate (500ppm), potassium sorbate (500ppm) and nisin (51U/ml). P. cyclohexanicum, although not inhibited by nisin (1000IU/ml), was susceptible to sodium benzoate (500ppm) and potassium sorbate (l000ppm). I-Ieadspace, movement of containers and storage temperatures affected detection rates of A. acjdoterrestrjs. Co-cultures demonstrated that if found within the same enviromnent, both bacilli can survive and cause spoilage. A. acidoterrestris is a world wide contaminant within the soft drinks industry and, considering the results of these studies P. cyclohexanicum with its heat resistance and tolerance to nisin may also emerge as a major spoilage microorganism