Series editors Inge Russell PhD, DSc, FIBD, FIBiol is the editor-in-chief of the J ournal of the Institute of Brewing , a visiting professor at Heriot-Watt University, Edinburgh, Scotland, an adjunct professor in the Department of Biochemical Engineering, University of Western Ontario, Canada, and director of the Alltech PhD Program. She has over 32 years experience in the fermentation industry as a research scientist and later directing the Research and Development for Labatt Brewing Company, Canada. She is the author of numerous books and papers as well as co-editor of C ritical Reviews in Biotechnology . Charles W. Bamforth PhD, DSc, FIBD, FIBiol, FIAFoST is currently the chair of the Department of Food Science and Technology and the Anheuser-Busch Endowed Professor of Malting and Brewing Sciences at the University of California, Davis. He has held positions as director of research for Brewing Research International and as research and quality assurance manager for Bass Breweries in the UK. He is the author of numerous books and papers as well as being the editor-in-chief of the J ournal of the American Society of Brewing Chemists . Graham G. Stewart PhD, DSc, FIBD, FIBiol is emeritus professor of brewing at Heriot-Watt University, Edinburgh, Scotland. Until 2007, he was professor and director of the International Centre for Brewing and Distilling (ICBD) at Heriot- Watt University. He previously held the position of technical director responsi- ble for research and development, quality assurance and technical training at the Labatt Brewing Company, Canada. He is the author of numerous books and papers as well as being co-editor of C ritical Reviews in Biotechnology . BBiioo--PP666699220011..iinndddd vviiii 66//2211//22000088 1111::5500::2288 AAMM List of contributors Charles W. Bamforth Department of Food Science and Technology, University of California, Davis, CA 95616-8598 Tel.: (cid:2) 1 530-752-9476 E-mail: [email protected] Alexander Ehmer Technical University Berlin, Research Institute for Chemical Technical Analyses, Seestrasse 13, 13353 Berlin Tel.: (cid:2) 49 30 314-27562 D. Evan Evans Tasmanian Instititute of Agricultural Research University of Tasmania Private Bag 54 Hobart Tas 7001 Australia Tel.: (cid:2) 61-(0)3-6226-2638; (cid:2) 61-(0)3-6226-2642 E-mail: eevans@postoffi ce.utas.edu.au Leif-Alexander Garbe Technical University Berlin, Research Institute for Chemical Technical Analyses, Seestrasse 13, 13353 Berlin Tel.: (cid:2) 49 30 314-27562 E-mail: [email protected]; [email protected] Anne E. Hill International Centre for Brewing and Distilling, School of Life Sciences, John Muir Building, Heriot Watt University, Riccarton Campus, Edinburgh, Midlothian, EH14 4AS E-mail: [email protected] Paul Hughes International Centre for Brewing and Distilling School of Life Sciences, Heriot- Watt University, Edinburgh, EH14 4AS, UK Tel: (cid:2) 44 131 451 3183 E-mail: [email protected] CCttrr--PP666699220011..iinndddd iixx 66//2211//22000088 1111::5511::1155 AAMM x List of contributors Kenneth A. Leiper International Centre for Brewing and Distilling School of Life Sciences, Heriot- Watt University, Edinburgh, EH14 4AS, UK Tel.: (cid:2) 44 131 451 3183 E-mail: [email protected] Aldo Lentini Foster’s Australia, National Supply Chain Operations, Beverages: Capability and Improvement, 4-6 Southampton Crescent, Abbotsford, Victoria, Australia 3067 Tel.: ( (cid:2) 61 3) 9420 6506 E-mail: [email protected] Michaela Miedl The International Centre for Brewing and Distilling (ICBD), School of Life Sciences, Heriot-Watt University, Riccarton EH14 4AS, Edinburgh, Scotland, UK Tel.: (cid:2) 44-131-451-3467 E-mail: [email protected]; [email protected] Paul Schwarz Barley and Malt Quality, Department of Plant Sciences, North Dakota State University, Fargo, ND 58105 Tel.: 701 231-7732 E-mail: [email protected] Thomas H. Shellhammer Department of Food Science and Technology, Oregon State University, 100 Wiegand Hall, Corvallis, OR 97331-6602 Tel.: 541.737.9308 E-mail: [email protected] CCttrr--PP666699220011..iinndddd xx 66//2211//22000088 1111::5511::1155 AAMM Preface Recent years have seen the emergence of several excellent books addressing the science and technology of brewing. We felt it important not to produce yet another volume of that type. Instead, we have approached matters some- what differently. We have focused on the quality of beer and the impact of raw materials and processing on each of the ways by which beer is perceived by the consumer. The ultimate requirement for beer, as for any foodstuff, is its accept- ability in the eyes, mouth and mind of the drinker. Such an approach has once before been taken, in E ssays in Brewing Science by Michael Lewis and myself (Springer, 2006). The difference is that, in the present work, the diverse authors were asked to “ dig deep ” into the richness and depth of research that has been devoted to the various quality attributes. On this basis, the aim has been to provide a thorough and extensively referenced treat- ment of all facets of beer appearance, fl avor, stability and wholesomeness. Upon pouring a beer into the glass, the drinker will make judgments on the acceptability of the product, based solely on what his or her eyes are seeing. We start the journey through the diverse quality criteria with Evan Evans and I considering the factors that determine foam stability. Inadequate foam perform- ance leads drinkers to conclude that the beer is of inferior quality. Of course, foaming can be done to excess, to the extreme that the contents of a bottle or can may spontaneously spew out when the container is opened. The factors that trigger this unacceptable defect are addressed at length by Leif- Alexander Garbe, Paul Schwarz and Alexander Ehmer. Having poured the beer successfully into the glass, with the desired amount of foam, the consumer is likely next to scrutinize the clarity of the liquid. Does it have the brilliance demanded – or, in a beer that is necessarily cloudy (such as a hefeweissen), is the extent of turbidity what is expected? Kenneth Leiper and Michaela Miedl cover in detail the impact that raw materials, process and product handling have on haziness. All beers, of course, have their specifi c color, whether it is the blackest stout or the palest lager. As for all other facets of product character, the color is impacted by raw materials and the manner by which they are dealt with in the production of beer. Thomas Shellhammer goes deep in his appreciation of this remarkably complex topic. At last, having critically judged the product for every manifestation of its appearance, the consumer is prepared to raise the glass of beer to be smelled PPrree--PP666699220011..iinndddd xxii 66//2211//22000088 1111::4499::1133 AAMM xii Preface and tasted. Does it taste right? Does it delight? Is it moreish? A myriad of chemical species combine to determine the rich complexity of beer aroma and taste and Paul Hughes walks us through them and how their levels in beer are achieved consistently. Beer fl avor, though, is not static. Most beers are never better than when fi rst brewed and packaged and the longer they are stored before consumption, the less and less appealing they become. Aldo Lentini and I explain the diverse changes that can take place and how they can be minimized. Whilst most of these fl avor changes are due to chemical reactions, any micro- bial contamination of beer will also lead to taste deterioration, as well as other quality defects, such as turbidity. Microbial contamination during the malting and brewing processes also has serious negative consequences. Anne Hill leads us through the breadth of microbiological concerns. And so the consumer has hopefully been delighted with a beer that has looked good and tasted good. The question is: Might it have actually done them some good? Increasingly the evidence is … yes … and I close out the volume by digging deep into the rich pool of evidence for beer’s worthy role as a legiti- mate component of the diet. The authors are internationally acclaimed experts in their fi elds, with repre- sentation from great schools in Germany, the United Kingdom, Australia and the United States. They have been brought together to deliver what we feel to be the most detailed and extensively referenced volume about beer quality yet written. The aim has also been to make it highly readable and enjoyable. As such, then, we expect it to prove an indispensable reference tome for research- ers in the fi eld and for brewers everywhere needing a one-stop resource for all facets of beer quality. But more, we expect it to appeal to anyone curious about the myriad of factors which make beer the outstanding beverage that it is. Professor Charlie Bamforth PhD, DSc, FIBD, FIBiol, FIAFoST California, USA PPrree--PP666699220011..iinndddd xxiiii 66//2211//22000088 1111::4499::1144 AAMM 1 Beer foam: achieving a suitable head D. Evan Evans and Charles W. Bamforth Introduction The aesthetic of drinking beer is to an extent subliminal. The presentation of the beer in the glass in terms of its foam head, clarity/brilliance and color conjure Pavlovian anticipation for the perceptive drinker. There is no disput- ing the logic that “ a beer drinker drinks as much with his or her eyes as with their mouth ” ( Bamforth et al., 1989 ). Other chapters in this book will offer insights into fl avor, fl avor stability, colloidal stability, color and the whole- someness of beer. That foam is perhaps one of the most appealing beer qualities is perhaps not surprising since the foam acts as an effi cient gas exchange surface pitch- ing aromas towards the drinkers olfactory sensors ( Delvaux et al., 1995 ). As such, it provides a drinker’s fi rst tantalizing entrée as to the quality of the beer’s fl avor, freshness, refreshingness and wholesomeness. Foam is also tactile to the lips and impacts mouthfeel through its stability and its struc- ture (bubble size). In part, this experience is modulated by the degassing of the beer in the mouth, which in turn is a function of beer carbonation/ nitrogenation ( Todd et al., 1996 ). Some may counter, “ most beer is drunk from a bottle. ” Well, yes it is, and beer bottles are often attractive and convenient in their own right, although the drinker is largely missing out on the fl avor cues extolled above. Bottles being glass are not opaque, particularly with the current fashion for clear and green varieties, so that they allow the drinker to clearly view foam formed as a result of the drinking action. In Belgium in particular, with branding of glass- ware, glass shape and material ( Delvaux et al., 1995 ), the glass has become an art form that almost supplants the bottle. Lastly, in attempting to compare beer with wine, in at least more up market settings, it would certainly be considered to be passé or uncouth to drink wine from the bottle! CChh0011--PP666699220011..iinndddd 11 66//2211//22000088 1100::3311::2211 AAMM 2 Beer: A Quality Perspective No brewer can afford to have their carefully crafted company or brand image downgraded by poor customer experiences. Given that the budget line for most brewers in the traditional beer countries is being expanded primarily by the provision of high margin premium beers, drinkers are perhaps more likely to pour the contents of the bottle in to a glass to savior the benefi ts out- lined above. If not from direct experience, “ alpha-beer drinkers ” who do pour their beer into a glass or customers who have purchased their beer dispensed off tap (draught) may prejudice their colleagues’ brand perception based on perceived excellent or poor experiences. Thus insurance of an excellent experi- ence for these infl uential drinkers and occasions is paramount in maintaining brand appeal. But what are the features of good foam quality? Typically, this is defi ned by a combination of its stability, quantity, lacing (glass adhesion or cling), white- ness, “ creaminess ” (small homo-disperse bubbles) and strength. Here “ beauty ” is defi nitely in the eye of the beholder as consumers discriminate between beers based on their foam characteristics. These choices have been found to diverge between genders, race or even region ( Bamforth, 2000a ; Smythe et al., 2002). Beer drinker 1 (a Belgian?) “Lively beer with good “Flat beer” “Great lacing, top beer!” head” Beer drinker 2 (a Londoner?) “Ripped off, foam is not “That is more like it, a full “A dirty glass” beer!” measure of beer” Beer drinker 3 (a Lady?) “Will this foam stick to “Not very lively and “This glass has not been my lip and wreck my appealing beer” properly cleaned before filling” make-up?” Figure 1.1 The perceptions of three different drinkers of beer foam quality. CChh0011--PP666699220011..iinndddd 22 66//2211//22000088 1100::3311::2211 AAMM Chapter 1 Beer foam: achieving a suitable head 3 Bamforth (2000a) concluded that “ there is a divide between consumers who like to see stable (but not excessive) head or foam but a clean glass at the end of drinking and those who favour a lacing pattern on the glass. ” More recently, it was demon- strated that men generally rate foam lacing higher than do women ( Roza et al., 2006 ). In addition, a female colleague pointed out the “ obvious. ” Some women tend to be adverse to foam because the thought of its adherence to their lips is unsettling, in that it could spoil their carefully applied make-up. Overall, these quandaries can perhaps be simply outlined pictorially as shown in Figure 1.1 . It is the intention of this chapter to comprehensively appraise the science underpinning beer foam quality. The discussion will begin by considering the basics of foam physics and how these principles can be applied to the task of measuring foam quality then extend to the basic biochemical constituents such as protein species and hop acids that combined determine foam quality. This holistic understanding is aimed at providing brewers with the best possible knowledge so that they may manipulate the raw materials, process and options for delivery to consistently produce the optimal foam quality that their targeted customers demand. Beer foam physics Elementary to an understanding of beer foam quality are the principles of beer foam physics that underlie the interaction of the various beer components, dis- pense and fi nally customer presentation, be it in a glass or some other container. The principles concerned have been comprehensively described by Dr Albert Prins ’ group of Wageningen ( Prins and Marle, 1999 ; Prins, 1988 ; Ronteltap, 1989 ; Ronteltap et al., 1991 ), and by others such as Walstra (1989) , Fisher et al. (1999) and Bamforth (2004a) . These authors have simplifi ed the somewhat com- plex physics involved into the following fundamental but interrelated events: ● Bubble formation and size ● Drainage ● Creaming (bubble rise or beading) ● Coalescence ● Disproportionation Bubble formation and size Despite beer being supersaturated with carbon dioxide, bubbles will not form spontaneously unless nucleation occurs ( Figure 1.2 ), promoted by a particle, fi ber or scratch in the glass ( Prins and Marle, 1999 ) or the dispense mode, be that tap ( Carroll, 1979 ) or bottle ( Skands et al., 1999 ). These nucle- ation sites should ideally be small to create smaller bubbles that create foam that is most appealing to the drinker ( Bamforth, 2004a ). A desirable attribute of nitrogenated beers, due to the lower partial pressure of nitrogen gas compared to CO , is the production of much smaller bubbles ( Carroll, 1979 ; Fisher et al., 2 CChh0011--PP666699220011..iinndddd 33 66//2211//22000088 1100::3311::2233 AAMM 4 Beer: A Quality Perspective Bubble Bubble Liquid Liquid Liquid Solid Gas Solid Solid pocket (1) Bubble nucleation (2) Bubble growth (3) Bubble detachment Figure 1.2 Schematic representation of the bubble formation sequence (after R onteltap et al., 1991). 1999 ). Such principles are applied in the use of nucleated glassware such as the “ headkeeper ” style ( Parish, 1997 ) or as a partial function of widgets ( Brown, 1997 ; Browne, 1996 ) which will be discussed later in the chapter. Finally, the control of dispense angle and low dynamic surface tension leads to smaller bubbles with a homeodisperse size distribution, which results in the desirable “ creamy ” foam characteristic ( Ronteltap et al., 1991 ). The factors governing the size of bubble that is generated in nucleation are described in the equation (1.1) Bubbleradius = ⎡⎢⎢3Rmγ⎤⎥⎥ 1/3 ⎣ 2ρg ⎦ (1.1) where R (cid:2) radius of nucleation site (m) m γ (cid:2) surface tension (mN m (cid:3) 1 ) ρ (cid:2) relative density of the beer (kg m (cid:3) 3 ) g (cid:2) acceleration due to gravity (9.8 m s (cid:3) 2 ) The radius of the nucleation site is very signifi cant, but surface tension and spe- cifi c gravity (relative density) are less important. Drainage Upon its formation, foam is usually termed to be “ wet. ” The excess beer in the foam rapidly drains by gravity to produce “ dry,” well drained foam in which more subtle effects of drainage can be discerned ( Figure 1.3 ). In the dry foam, continued beer drainage by gravity and “ Plateau border suction ” weakens the bubble fi lm eventually leading to bubble collapse ( Ronteltap et al., 1991 ). Ronteltap et al. (1991) concludes that the counteracting forces to drainage are vis- cosity of the beer, capillary effects and the beer’s surface viscosity. The infl uence of beer viscosity is consistent with beer foam being observed to be more stable at lower temperatures. This explanation was more recently simplifi ed to con- clude that surface viscosity as opposed to bulk viscosity was most important CChh0011--PP666699220011..iinndddd 44 66//2211//22000088 1100::3311::2233 AAMM