125th Anniversary Review: Microbiological Instability of Beer Caused by Spoilage Bacteria

Beer has been generally recognized as a microbiologically stable beverage. However, microbiological incidents occasionally occur in the brewing industry. The microbiological instability of beer is often caused by bacteria consisting of four genera, Lactobacillus, Pediococcus, Pectinatus and Megasphaera. Lactobacillus and Pediococcus belong to the lactic acid bacteria (LAB), whereas Pectinatus and Megasphaera form a group of strict anaerobes that are known as intermediates between Gram‐positive and Gram‐negative bacteria. The frequencies of beer spoilage incidents caused by these four genera have been reported to exceed 90% in Europe and therefore Lactobacillus, Pediococcus, Pectinatus and Megasphaera are considered to be the principal spoilage agents in the brewing industry. Thus, this review consists of three parts involving these four genera. The first part describes spoilage LAB in alcoholic beverages with some emphasis on beer spoilage LAB. In this part, the emergence and evolution of these spoilage LAB is discussed, the insight of which is useful for developing quality control methods for these beverages. The second part is devoted to the hop resistance in beer spoilage LAB. This area of research is evolving rapidly and recent progress in this field is summarized. The third part concerns Pectinatus and Megasphaera. Although this group of beer spoilage bacteria has been described relatively recently, the incident reports in Europe increased in the early 1990s, reaching around 30% of spoilage incidents. Various aspects of Pectinatus and Megasphaera, ranging from their taxonomy and beer spoilage ability to detection and eradication methods are described.     

125th Anniversary Review: Water sources and treatment in brewing

At one time the raw water naturally available influenced the development of typical regional beer styles. With the development of reliable and efficient water treatment technologies, breweries became independent of the local raw water quality. The proliferation of large breweries is still closely linked to progress in water treatment. The prevailing question is always how to best condition the raw water for the different purposes within the brewery in the most efficient way. The raw water starting points are very different and can range from well water, to surface water, to municipal water, and in some cases to more exotic water sources such as rain or even treated wastewater. The impact of different water ions on the brewing process is discussed, with a special focus on technological requirements, as well as microbiology and corrosion issues. The requirements of divergent water types commonly used for brewing, dilution, service and boiler feed water, and available treatment steps based on examples of large‐sized plants are discussed, including traditional methods such as lime softening and ion exchange, as well as more recent treatment systems. Membrane technology is highlighted, as it has had a great impact on treatment technology. Following the success story of reverse osmosis, and more recently developed ultrafiltration, there is now more focus on special applications such as the substitution of lime saturators to produce clear lime water with membranes. This requires higher performance and robustness of the membranes. Finally, some future challenges for water treatment in breweries are outlined. Copyright © 2012 The Institute of Brewing & Distilling     

125th Anniversary Review: Advances in analytical methodology in brewing

Comprehensive sets of chemical, microbiological and sensory methods have long been available to characterize individual beers and explore the relationships between raw materials, process conditions and the outcome of the brewing process. Although the majority of major brewers are increasingly using quality assurance as opposed to quality control as the basis of operation, the need to use chemical analyses is still perceived as an essential prerequisite to brewing. The requirement to meet the various legislative codes and the need to manage the consistency of international brands arising from several individual breweries make the possession of robust analytical procedures essential. In many breweries there is a trend towards devolving traditional analytical tasks from central quality control laboratories manned by dedicated technicians to satellite stations, where the analyses needed to support production are performed directly by process workers. Parallel to these changes is a desire to achieve a greater understanding of the complex relationships between beer analysis and overall quality, in particular, the identification of markers that allow for the identification of processes such as beer ageing. This review summarizes the ways in which brewing analytical methods and the suppliers of analytical apparatus are evolving to meet the needs of the current modern industry. Copyright © 2012 The Institute of Brewing & Distilling     

125th Anniversary Review: The science of the tropical cereals sorghum,maize and rice in relation to lager beer brewing

Mainstream lager beer brewing using the tropical cereals sorghum, maize and rice, either as malt or as raw grain plus commercial enzymes, is becoming widespread. This review examines the differences in composition between these tropical cereals and barley and their impact on brewing processes and beer quality. All of these cereals have a starch gelatinization temperature some 10 °C higher than barley. The sorghum prolamin proteins are particularly resistant to proteolysis owing to disulphide cross‐linking involving γ‐kafirin. Unlike barley, the major endosperm cell wall components in sorghum and maize are arabinoxylans, which persist during malting. The rice cell walls also seem to contain pectic substances. Notably, certain sorghum varieties, the tannin‐type sorghums, contain considerable levels of condensed tannins (proanthocyanidins), which can substantially inhibit amylases, and probably also other brewing enzymes. Tropical cereal malts exhibit a similar complement of enzymic activities to barley malt, with the notable exception of β‐amylase, which is much lower and essentially is absent in their raw grain. Concerning beer flavour, it is probable that condensed tannins, where present in sorghum, could contribute to bitterness and astringency. The compound 2‐acetyl‐1‐pyrroline, responsible for the popcorn aroma of maize and also the major aroma compound in rice, presumably affects beer flavour. However, much more research is needed into tropical cereals and beer flavour. Other future directions should include improving hydrolysis of prolamins into free amino nitrogen, possibly using prolyl carboxypeptidases and investigating tropical cereal lines with useful novel traits such as high amylopectin, high protein digestibility and low phytate. Copyright © 2013 The Institute of Brewing & Distilling     

125th Anniversary Review: The importance of learning

Learning has been at the heart of mankind's advances from ‘hunter gatherer’ to ‘organized’ and continues to be at the core of the development of our civilization. Learning takes many forms – we can learn by observation and by demonstration and we can learn from outcomes and from deliberate experimentation. Acquired knowledge is preserved and new knowledge added ‘to the bank’ through the written word and through the wisdom of individuals. Knowledge underpins how and why we do things and forms the basis of developing new ideas. If knowledge is not shared and then acquired by individuals, then those individuals will be at a competitive disadvantage to their peers. Organizations that develop and nurture their knowledge pool will demonstrate superior performance and engender a more innovative and dynamic working environment. Copyright © 2012 The Institute of Brewing & Distilling     

125th Anniversary Review: The Role of Hops in Brewing

Although hop technology has been a substantial part of brewing science for the last 130 years, we are still far from claiming to know everything about hops. As hops are considered primarily as a flavour ingredient for beer, with the added benefit of having anti‐microbial effects, hop research is focused on hops as a bittering agent, as an aroma contributor and as a preservative. Newer fields in hop research are directed toward the relevance of hops in flavour stability, brewing process utilisation, the technological benefits of hops in brewing as well as hops as a source of various substances with many health benefits. However the more we find out about the so‐called “spirit of beer” the more questions emerge that demand answers. While hop research was only an ancillary research field for decades, during the last ten years more universities and breweries have determined that hops must play a meaningful role in their research efforts. This article gives an overview of the up‐to‐date knowledge on hop aroma, hop derived bitterness, and the role of hops in flavour stability as well as light stability. Hop research is a wide field, therefore in this review only selected topics are reviewed. Other research areas such as hops utilisation, the antifoam potential of hops, or the advances in knowledge pertaining to the physiological valuable substances of hops go beyond the scope of this article.     

肉及肉制品中的细菌

细菌是个体微小、形态简单的一类原核微生物。在自然界中,数量最多、分布最广,是导致食品腐败变质的主要原因。因此,本文对细菌的基本形态、结构、繁殖方式以及肉及肉制品中常见细菌的特性进行了综述,旨在为肉及肉制品中细菌的控制及防范,提供一定的理论依据。     

市售食用菌鲜品外源细菌的动态变化分析

目前,市售食用菌鲜品大多保藏于常温条件下,食用菌因营养丰富、表面组织鲜嫩而更易滋生外源微生物。以市售常温保藏的金针菇、杏鲍菇、蟹味菇鲜品为材料,分析货架期内其外源细菌数量、种类、群落多样性的变化。结果表明,3种食用菌在货架期内外源细菌数量明显增加,货架期5 d蟹味菇增长了29倍,金针菇、杏鲍菇分别增长了417、4 116倍。外源细菌种类及相对丰度在货架期呈动态变化,表现为优势菌在货架期1~5 d能够被检测到,蟹味菇假单胞菌属丰度增加和金针菇乳球菌属丰度降低。Shannon指数表明在货架期内,金针菇外源细菌多样性明显低于杏鲍菇和蟹味菇。主成分分析结果表明,3种食用菌各自在不同货架期内菌群结构呈现相似性,蟹味菇和杏鲍菇外源细菌菌群结构存在一定的相似性,金针菇外源细菌菌群结构与蟹味菇和杏鲍菇存在差异。     

125th Anniversary Review: Yeast Flocculation and Sedimentation in Brewing

Flocculation is prerequisite for bulk sedimentation of yeast during brewery fermentation. Although single yeast cells gradually sediment in green beer, this sedimentation rate is too slow without formation of large yeast flocs. The present review concerns the major determinants of yeast flocculation and sedimentation in brewery fermentations. Flocculation characteristics of yeast are strongly strain‐dependent and largely defined by which FLO genes are functional in each strain. In addition to the genetic background, several environmental factors affect flocculation. These can be, somewhat arbitrarily, classified as physiological factors, such as the calcium availability, pH, temperature and ethanol and oxygen concentrations in the medium or physical factors, such as cell surface hydrophobicity, cell surface charge and the presence of appropriate hydrodynamic conditions for the formation of large flocs. Once yeast flocs are formed, their size, shape and density and the properties of the surrounding medium affect the rate at which the flocs sediment. Higher gravity worts usually result in green beers with higher viscosity and density, which both retard sedimentation. Moreover, environmental factors during yeast handling before fermentation, e.g., propagation, storage and cropping, influence the flocculation potential of yeast in subsequent fermentation. Premature yeast flocculation (PYF) and the role of PYF factors are discussed. In conclusion, some potential options available to adjust yeast flocculation are described.     

125th Anniversary Review: The role of proteins in beer redox stability

Flavour stability is usually approached through inhibition of reactive oxygen species (ROS). It may be possible to suppress ROS, but never to entirely eliminate them in packaged beer. The role of proteins in ROS suppression seems to have been lost in the compliant acquiescence to supply haze‐free bright beer. Proteomics allows beer polypeptides to be finely resolved, identified and correlated with beer quality and stability. This has already produced a broader view of what stabilizes beer foam. No doubt it could do the same for beer stability and the broader roles that proteins, such as LTP1, can have in redox reactions and free radical suppression. Cysteine oxidation and reversibility is central to cellular signalling in biological systems. Thiol chemistry is also integral to beer redox stability. We can, and should, extrapolate the recent biological findings to the simple pleasure of creating a high‐quality beer. Copyright © 2012 The Institute of Brewing & Distilling     

125th Anniversary Review: The Non‐Biological Instability of Beer

Unlike many alcoholic beverages beer is inherently unstable. In chemical (as opposed to microbiological) terms this instability can be considered — and is here reviewed — in the categories of colloidal instability, foam, gushing, flavour instability and light sensitivity     

125th Anniversary Review: Diacetyl and its control during brewery fermentation

Diacetyl is a butter‐tasting vicinal diketone produced as a by‐product of yeast valine metabolism during fermentation. Concentration is dependent on a number of factors including rate of formation of the precursor α‐acetolactate by yeast, spontaneous decarboxylation of this acetohydroxy acid to diacetyl and removal of diacetyl by yeast via the action of various reductase enzymes. Lowering concentrations of diacetyl in green beer represents an expensive and time‐consuming part of the brewing process and strategies to minimize diacetyl formation or hasten its reduction have potential for improving overall efficiency of the lager brewing system. Here we review the processes that determine diacetyl levels in green beer as well as the various ways in which diacetyl levels can be controlled. The amount of diacetyl produced during fermentation can be affected by modifying process conditions, wort composition or fermentation technique, or by yeast strain development through genetic engineering or adaptive evolution. The process of diacetyl reduction by yeast is not as well understood as the process of formation, but is dependent on factors such as physiological condition, cell membrane composition, temperature and pH. The process of diacetyl removal is typically rate‐limited by the reaction rate for the spontaneous decarboxylation of α‐acetolactate to diacetyl. Copyright © 2013 The Institute of Brewing & Distilling     

125th Anniversary Review: Some Recent Engineering Advances in Brewing and Distilling

Some of the more important engineering advances of the last 25 years in brewing and distilling are reviewed. The modern mash filter is compared to lauter tuns. Wort boiling systems, cross‐flow or membrane filtration, yeast propagation, and process improvements are considered. Approaches taken to reducing energy, water and effluent are highlighted, as is by‐product usage. The impact of computers, software, and digital technology on process control, automation, engineering design, and project implementation are reviewed.     

125th Anniversary Review: Fuel Alcohol: Current Production and Future Challenges

Global research and industrial development of liquid transportation biofuels are moving at a rapid pace. This is mainly due to the significant roles played by biofuels in decarbonising our future energy needs, since they act to mitigate the deleterious impacts of greenhouse gas emissions to the atmosphere that are contributors of climate change. Governmental obligations and international directives that mandate the blending of biofuels in petrol and diesel are also acting as great stimuli to this expanding industrial sector. Currently, the predominant liquid biofuel is bioethanol (fuel alcohol) and its worldwide production is dominated by maize‐based and sugar cane‐based processes in North and South America, respectively. In Europe, fuel alcohol production employs primarily wheat and sugar beet. Potable distilled spirit production and fuel alcohol processes share many similarities in terms of starch bioconversion, fermentation, distillation and co‐product utilisation, but there are some key differences. For example, in certain bioethanol fermentations, it is now possible to yield consistently high ethanol concentrations of ˜20% (v/v). Emerging fuel alcohol processes exploit lignocellulosic feedstocks and scientific and technological constraints involved in depolymerising these materials and efficiently fermenting the hydrolysate sugars are being overcome. These so‐called second‐generation fuel alcohol processes are much more environmentally and ethically acceptable compared with exploitation of starch and sugar resources, especially when considering utilisation of residual agricultural biomass and biowastes. This review covers both first and second‐generation bioethanol processes with a focus on current challenges and future opportunities of lignocellulose‐to‐ethanol as this technology moves from demonstration pilot‐plants to full‐scale industrial facilities.     

酱油腐败菌的分离鉴定与性质研究

乳酸菌和肠杆菌在传统食品的发酵中易引起食品腐败。本研究从传统酱醅和胀罐酱油中分离筛选到3株疑似腐败菌,对其进行形态、生理生化特性研究及16S rDNA序列分析,结合PCR-RFLP、ERIC-PCR及Species-Specific PCR,最终分别鉴定为产气肠杆菌、屎肠球菌(从酱醅中分离到)和马里乳杆菌(从胀罐酱油中分离到)。研究表明,产气肠杆菌具有极强产气性、而马里乳杆菌也具微弱产气性;将这三株菌接种到成品酱油中发现,均能微弱改变酱油pH值;同时这三株菌均对温度、pH、盐度具有耐受性;产气肠杆菌和屎肠球菌为条件致病菌,对消费者存在潜在危害,同时本研究发现马里乳杆菌的存在会引起酱油胀气、降低pH,从而导致酱油腐败。这三株菌的分离鉴定,对酱油的质量保证和食用安全性具有重要意义。     

冷却猪肉优势腐败菌分离鉴定及致腐能力测定

分离鉴定冷却猪肉中的优势腐败菌并测定其致腐能力,以研究冷却肉腐败机理。利用选择性培养基和感官评定方法,从变质冷却猪肉中分离筛选出优势腐败菌并鉴定到种。再将各优势腐败菌接种到灭菌肉块上,4℃贮藏下定期测定各腐败菌的菌落数和挥发性盐基氮(TVB-N),并以TVB-N产量因子(YTVB-N)衡量各腐败菌的致腐能力。结果表明:经选择性培养基分离和肉样感官评定共筛选得到5株优势腐败菌即P3、PS1、J4、P5和S5,分别鉴定为Acinetobacter guillouiae、Pseudomonas koreensis、Bacillus fusiformis、Enterobacter cloacae和Brochothrixthermosphacta。进一步研究其腐败特性发现,4℃贮藏时接种优势腐败菌的肉样在第7天已明显腐败。PS1的TVB-N和YTVB-N明显高于其他菌株。研究表明,从冷却猪肉分离鉴定出的优势腐败菌中,PS1导致冷却猪肉腐败能力较强。     

引起哈密瓜采后腐败变质的病原菌分离鉴定

为了调查微生物与哈密瓜采后腐败变质的关系,采用传统微生物培养技术研究不同温度保藏过程中哈密瓜表皮可培养微生物动态变化.研究发现,造成哈密瓜采后贮藏期间腐烂的主要病原菌包括镰刀属、链格孢属、青霉属,此外还有葡萄球菌属等.青霉菌和镰刀菌是引起哈密瓜在低温贮藏或冷藏运输过程中导致其腐烂的优势病原菌.本研究说明哈密瓜的腐败是单...     

食源性致病菌和腐败菌的快速检测方法研究进展

食源性致病菌和腐败菌污染一直是引发食品安全事件的重要因素。传统的检测方法虽具有较高的准确性,但需培养及生化实验,耗费时间长且操作较复杂,开发高效、快速的检测方法对保障食品安全至关重要。近年来,科学技术的进步使一些新方法、新技术逐渐被运用,比传统培养法检测时间更短、效率更高、特异性更好,具有广阔的应用前景。因此,本文综述了食源性致病菌和腐败菌快速检测方法的最新研究进展,包括纸片法、流式细胞术、阻抗法、腺苷三磷酸荧光法、光谱检测技术、分子生物学检测技术、免疫学检测法及生物传感器检测技术等,着重论述了各种方法的原理、优缺点、应用状况及发展方向,为致病菌和腐败菌引发的食品安全事件的预防及控制提供参考。     

Lactic Acid Bacteria as Antifungal and Anti‐Mycotoxigenic Agents: A Comprehensive Review

Fungal contamination of food and animal feed, especially by mycotoxigenic fungi, is not only a global food quality concern for food manufacturers, but it also poses serious health concerns because of the production of a variety of mycotoxins, some of which present considerable food safety challenges. In today's mega‐scale food and feed productions, which involve a number of processing steps and the use of a variety of ingredients, fungal contamination is regarded as unavoidable, even good manufacturing practices are followed. Chemical preservatives, to some extent, are successful in retarding microbial growth and achieving considerably longer shelf‐life. However, the increasing demand for clean label products requires manufacturers to find natural alternatives to replace chemically derived ingredients to guarantee the clean label. Lactic acid bacteria (LAB), with the status generally recognized as safe (GRAS), are apprehended as an apt choice to be used as natural preservatives in food and animal feed to control fungal growth and subsequent mycotoxin production. LAB species produce a vast spectrum of antifungal metabolites to inhibit fungal growth; and also have the capacity to adsorb, degrade, or detoxify fungal mycotoxins including ochratoxins, aflatoxins, and Fusarium toxins. The potential of many LAB species to circumvent spoilage associated with fungi has been exploited in a variety of human food and animal feed stuff. This review provides the most recent updates on the ability of LAB to serve as antifungal and anti‐mycotoxigenic agents. In addition, some recent trends of the use of LAB as biopreservative agents against fungal growth and mycotoxin production are highlighted.