Kellershohn / Russell / Stewart Beer

A Quality Perspective
1. Auflage 2011
ISBN: 978-0-08-092609-4
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 304 Seiten

Reihe: Handbook of Alcoholic Beverages

Beer is the only detailed book that specifically addresses the science of beer quality. It explores the quality attributes of beer as well as the various impacts on and perception of beer quality. It includes expert insights based on real-world experience. This book details, with extensive referencing, the research that has been devoted to beer and beer quality. It is the first book to approach beer in this way and comprises an essential reference for anyone seeking an authoritative account of the science of beer appearance, flavor, stability and wholesomeness. Chapters discuss beer foam and how to achieve a suitable head; beer flavour and its instability; colloidal stability of beer; microbiological stability of beer; beer gushing; beer color; and the health aspects of beer. This book will be of interest to employees on the technical production side of the alcoholic beverage industry; students studying the subject; people involved in related and associated biotechnology industries; people from the brewing industry; and academic researchers. - The only detailed book that specifically addresses the science of beer quality - Addresses the various impacts on and perception of beer quality - Includes expert insights based on real-world experience

Autoren/Hrsg.

Kellershohn, Julie

Russell, Inge

Stewart, Graham

Inhaltsverzeichnis

1;Front cover;1
2;Beer: A Quality perspective;2
3;Copyright page;3
4;Contents;4
5;Series editors;8
6;List of contributors;10
7;Preface;12
8;Chapter 1 Beer foam: achieving a suitable head;14
8.1;Introduction;14
8.2;Beer foam physics;16
8.3;Foam measurement;21
8.4;Beer components that influence foam quality;25
8.5;Proteins;26
8.6;Non-starch polysaccharides;34
8.7;Hop acids;35
8.8;Cations;38
8.9;Lipids;38
8.10;Other foam negative/positive beer constituents;39
8.11;Manipulating the brewing process to optimize foam quality;41
8.12;Summary;61
8.13;Acknowledgments;61
8.14;References;61
9;Chapter 2 Beer flavor;74
9.1;Introduction;74
9.2;The flavor unit;74
9.3;Brewing raw materials and beer flavor;75
9.4;Impact of beer production processes;85
9.5;In-pack flavor changes;91
9.6;Taints and off-flavors;93
9.7;Holistic flavor perception;94
9.8;Summary;95
9.9;References;95
10;Chapter 3 The flavor instability of beer;98
10.1;Factors impacting the shelf life of beer;101
10.2;The impact of temperature;108
10.3;The chemistry of flavor change in beer;109
10.4;An evaluation of processes from barley to beer in the context of flavor instability;113
10.5;References;118
11;Chapter 4 Colloidal stability of beer;124
11.1;Summary;124
11.2;Biological stability;125
11.3;Importance of whole process to ensure stability;125
11.4;Chill haze;127
11.5;Protein in beer;127
11.6;Beer polypeptides and their functions;129
11.7;Identifying polypeptides by size;130
11.8;Identifying polypeptides by amino acid composition;138
11.9;Identifying polypeptides by hydrophobicity;143
11.10;Summary of polypeptides;145
11.11;Polyphenols;147
11.12;Methods of detecting polyphenols;148
11.13;Polyphenols in beer;148
11.14;Haze-forming reactions between polypeptides and polyphenols;151
11.15;Stabilization treatments;153
11.16;Combined stabilization system (CSS);163
11.17;Other treatments;163
11.18;Other non-biological hazes;164
11.19;Testing the effectiveness of beer stabilization;165
11.20;Haze identification;167
11.21;References;167
12;Chapter 5 Microbiological stability of beer;176
12.1;Overview of microbial spoilage;176
12.2;Outline of the brewing process;177
12.3;Raw materials;178
12.4;Wort;182
12.5;Fermentation;182
12.6;Storage and finishing;183
12.7;Packaging and packaged beer;183
12.8;Dispense;184
12.9;Detection;184
12.10;Improving microbiological stability;191
12.11;Quality control;193
12.12;References;194
13;Chapter 6 Beer gushing;198
13.1;Introduction;198
13.2;Terminology;199
13.3;Physical background of gushing;200
13.4;Primary gushing;201
13.5;Secondary gushing;214
13.6;Summary;217
13.7;References;218
14;Chapter 7 Beer color;226
14.1;Color perception;226
14.2;Measuring color;227
14.3;Standard methods for measuring beer color;231
14.4;Origins of beer color;234
14.5;References;239
15;Chapter 8 Beer and health;242
15.1;Atherosclerosis;245
15.2;Hypertension and stroke;248
15.3;The digestive system;248
15.4;The reproductive system;250
15.5;Brain and cognitive function;250
15.6;Kidney and urinary tract;252
15.7;Age;252
15.8;Cancer;253
15.9;Allergy;254
15.10;References;255
16;Appendix: Practicalities of achieving quality;268
16.1;Definitions of quality;268
16.2;Responsibility for quality;269
16.3;Quality systems;269
16.4;Quality assurance versus quality control;270
16.5;Specifications;271
16.6;The cost of quality;271
16.7;Statistical process control;272
16.8;Process capability;274
16.9;Control charts;274
16.10;Standard methods of analysis;275
16.11;Setting specifications and monitoring performance;283
16.12;Hazard analysis critical control points (HACCP);284
17;Index;292
17.1;A;292
17.2;B;292
17.3;C;293
17.4;D;294
17.5;E;294
17.6;F;294
17.7;G;296
17.8;H;296
17.9;I;297
17.10;K;297
17.11;L;297
17.12;M;297
17.13;N;298
17.14;O;298
17.15;P;298
17.16;Q;299
17.17;R;299
17.18;S;299
17.19;T;300
17.20;U;300
17.21;V;300
17.22;W;301
17.23;X;301
17.24;Y;301
17.25;Z;301

Leseproben

2 Beer flavor Paul Hughes Introduction
The flavor attributes of beer are critical to its overall acceptance by consumers. Whilst beer has been defined as the second most bland drink after milk (presumably excluding water!), beer flavor is the ultimate expression of a rather complex series of production processes. Additionally, with the exception of a handful of examples1 there are few practical options for the substantial removal of components from beer during production, which limits the opportunities for remedial action. This implies that, for product consistency, a fine degree of control is required. This is particularly relevant for beer flavor, where the typical dynamic range of flavor perception ranges from sub-ppt (low picomolar) to high-ppm (high millimolar) concentrations, or 11–12 orders of magnitude. In this chapter, we start by reiterating the flavor unit (FU) concept originally expounded by Meilgaard. We then survey beer flavor as the interaction of malting and beer production processes with brewing raw materials. There are two other broad sources of flavors in beer: those that develop during beer storage, and those that are not normally present in beer that are derived from accidental contact with contaminated materials, the so-called taints. This approach, though, considers beer in terms of its specific components, so we close this chapter by appraising beer flavor in more holistic (i.e. consumer relevant) terms, and outline approaches for the assessment of beer flavor attributes. The flavor unit
The comparison of analytical data for flavor compounds in beers is difficult to understand in sensory terms without an appreciation of the flavor thresholds of each of the analytes. Thus, whilst 15 ppb of hydrogen sulfide is sensorially significant, for dimethyl sulfide the flavor impact is much less or even absent at the same concentration. Meilgaard (1975) proposed the correction of analytical figures with flavor threshold estimates to derive the flavor unit (FU). The result is a set of analytical data that is scaled according to our ability to perceive it.
     (2.1)
(Note: FU is dimensionless and therefore the units of analysis and threshold must be the same). There are limitations to such an approach, not least of which is the variation of individuals’ thresholds but, nonetheless, it does help to evaluate the significance of changes in flavor compound concentration. For instance, viewing analytical data in this way (Figure 2.1) shows clearly that there are typically few compounds that exceed their flavor threshold in beer and implies a total FU score for a given product. Such a score can be substantially distorted by the introduction of certain off-flavors or taints. Figure 2.1 An incomplete Flavor Unit (FU) plot for a typical European lager beer. Few compounds are present at above flavor threshold. The introduction of taints or off-flavors can substantially distort this plot. For instance, modest exposure of beer to light will result in the development of FUs of MBT (3-methyl-2-butene-1-thiol) that exceed the total FUs for the rest of the beer flavor impact characters. Brewing raw materials and beer flavor
Quantitatively, the most important raw materials used for the production of beer are the carbohydrate sources, that is barley (usually malted), adjuncts such as maize, wheat and sorghum. Less commonly oats, and, in some instances, flavored sugars (e.g. chip sugar) also confer flavor on beer when they are pressed into service. However, in terms of raw materials, it is the use of hops that uniquely defines the direct raw material contribution to beer flavor. Hops imbue beer with its characteristic bitterness and in many cases can provide an appreciable hoppy aroma to the final product. This is dependent on the way in which hops are used and, indeed, there are now a plethora of hop products available to the brewer to allow downstream adjustment of final hoppy flavors in beer independent of bitterness. Malted barley
Malted barley is the major raw material for most beers produced world-wide. The vast majority of this is white malt, which is so-called because it is kilned primarily to remove the water absorbed during germination, rather than to generate color. The act of kilning also helps to reduce the levels of flavor-negative green notes which are characteristic of unkilned malt and due to the presence of aldehydes such as hexanal. The degree of color formation during kilning positively correlates to the formation of increasing amounts of flavor-active Maillard reaction products, which are inevitable given that the main aim of the malting process is to release fermentable carbohydrates and free amino nitrogen for subsequent fermentation. Thus the use of specialty malts, which are applied in smaller proportions, adds both color and flavor to the final beer (Table 2.1). Table 2.1 Typical flavors derived from specialty malts (Hughes and Baxter, 2001) The heat-promoted chemical reactions that occur during malt kilning are complex, including the thermal degradation of phenolic acids, the caramelization of sugars, Maillard reactions (including the Strecker degradation of amino acids), and thermal degradation of oxygenated fatty acids derived both chemically and enzymically from lipids (Figure 2.2). Thus a range of volatile compounds are formed, such as fatty acids, aldehydes, alcohols, furans, ketones, phenols, pyrazines and sulfur compounds. Compounds such as furaneol, maltol and isomaltol (Table 2.2) are highly flavor-active and can contribute to beer flavor. During the course of the Maillard reaction cascade, the oxygen of furan rings may be replaced by sulfur or nitrogen moieties, leading to the formation of the corresponding thiophenes and pyrroles. Other malt-derived heterocycles identified in malt include thiazoles, thiazolines, pyridines, pyrrolizines and pyrazines. Some pyrazines, such as the dimethylpyrazines, can occur at levels above two flavor units in some cases, thereby substantially affecting beer flavor (Herent et al., 1997). These heterocycles have a diverse range of flavor attributes, and have been variously described as malty, oxidized, sweet, meaty and burnt. Figure 2.2 An overview of the Maillard reaction cascade (Hughes and Baxter, 2001). These reaction pathways are affected by various parameters, not least temperature, pH and water-activity. Table 2.2 Flavor-active Maillard compounds found in malts (Hughes and Baxter, 2001) The presence of these compounds in malt indicates that they are likely to occur in sweet wort. However, many are lost during the boiling stage either by evaporation or chemical breakdown and during fermentation, by the action of yeast. Of those that survive into beer, dimethyl sulfide (DMS) is one of the most significant, particularly for lager beers. A significant component of malt is lipid – typically 3% (w/w) of the dry grain (Palmer, 2006). Most of this material, being relatively insoluble in aqueous media, is lost with the brewers’ grains or precipitated with the solids (trub) which are formed both during the boil and during the subsequent cooling operations. The major fatty acid component is linoleic acid, which can yield many C5–C12 saturated and unsaturated aldehydes, ketones and alcohols, some of which are highly flavor-active. This is discussed further below. Hop compounds
Much of the bitterness of beer is due to the presence of the iso-a-acids. These are a mixture of six major components, which are three stereoisomeric pairs of compounds derived from each of the three hop a-acids (Figure 2.3a). These a-acids are isomerized to the iso-a-acids during the wort boiling stage, although in practice the final utilization is around 30–40%. In contrast, isomerization by hop processing outwith the brewery (Figure 2.3a) gives yields in excess of 90%. There are probably minor differences in the bitterness of the individual compounds. Nevertheless, whilst hops come in a wide range of varieties, current thinking is that variety has little effect on bitterness intensity or quality. There are some who consider the cohumulone content of the a-acids to have poorer quality bitterness, but to date this has not been conclusively demonstrated. It is likely though that the utilization of the isocohumulones is significantly higher than the other iso-a-acids, which can be attributed to their lesser hydrophobicity, so they are more readily retained in solution. Figure 2.3 Hop acid contributors to beer bitterness. (a) The formation of the bitter iso-a-acids from the non-bitter a-acids; (b) the three groups of chemically modified iso-a-acids; (c) the formation of hulupones from oxidative degradation of the ß-acids. Hops also contain the ß-acids. Although these do not undergo isomerization in the sense of a-acids, they do form bitter degradation products – the hulupones – when present during wort boiling (Figure 2.3c). In practice, this contribution...