Essays in Brewing Science

184 Pages·2007·1.32 MB·English

by  Michael J. Lewis

Essays in Brewing Science
Essays in Brewing Science
Michael J. Lewis and
Charles W. Bamforth
UniversityofCalifornia–Davis
Davis,California,USA
MichaelJ.Lewis Charles.W.Bamforth
ProfessorEmeritusofBrewingScience Chairperson,DepartmentofFoodScience
AcademicDirectorofBrewing andTechnology
ProgramsinUniversityExtension Anheuser-BushEndowedProfessor
UniversityofCalifornia–Davis UniversityofCalifornia–Davis
Davis,California95616-8598 Davis,California95616-8598
e-mail:[email protected] e-mail:[email protected]
LibraryofCongressControlNumber:2006923489
ISBN10:0-387-33010-0 e-ISBN10:0-387-33011-9
ISBN13:978-0387-33010-5 e-ISBN13:978-0387-33011-2
Printedonacid-freepaper.
(cid:2)C 2006SpringerScience+BusinessMedia,LLC
Allrightsreserved.Thisworkmaynotbetranslatedorcopiedinwholeorinpartwithoutthe
writtenpermissionofthepublisher(SpringerScience+BusinessMedia,LLC,233SpringStreet,
NewYork,NY10013,USA),exceptforbriefexcerptsinconnectionwithreviewsorscholarly
analysis. Use in connection with any form of information storage and retrieval, electronic
adaptation,computersoftware,orbysimilarordissimilarmethodologynowknownorhereafter
developedisforbidden.
Theuseinthispublicationoftradenames,trademarks,servicemarks,andsimilarterms,even
iftheyarenotidentifiedassuch,isnottobetakenasanexpressionofopinionastowhether
ornottheyaresubjecttoproprietaryrights.
9 8 7 6 5 4 3 2 1
springer.com
Preface
Most brewing texts use a systematic barley-beer-bottle organization that
takes the reader sequentially through the various stages of beer-making.
This, of course, is logical and useful and works well. However, brewers do
notoftenthinkaboutbeerandbrewinginthisway,e.g.tosolveproblems,
buttheythinkaboutallthestagesintheprocessthatmightgetaffected,e.g.
asinglebeerpropertysuchascolor.Alternatively,brewersmightponderon
theinfluenceofsuchaffectiveagentsasmodificationoroxygenthroughout
the process. This is also a typical questioning strategy in the examinations
of the Institute of Brewing and Distilling that many professional brewers
take. We think of this as a longitudinal organization of the subject matter,
i.e. looking down the length of the process for causes and effects, and that
is the structural approach to this book. It is important to bear this in mind
when reading the book because this organization brings together informa-
tion and ideas that are not usually seen side-by-side, and material that is
usually in a single chapter in most books might be spread over several in
this one because that best suits the unifying theme of the chapters. It has
been relatively easy to draw together, from across the spectrum of beer-
making, material that affects such beer properties as color, foam and haze,
for example, for which this organizational structure works quite well; how-
ever, in other cases the structure has given us some surprises and, to fulfill
theconceptofthebook,e.g.wortboilingappearsunderachapteronwater
v
vi Preface
andenergy.Therefore,thoughwethinkofeachchapterasastand-alonees-
sayonthenominatedtopic,wehavebeenatsomepainstocross-reference
thechaptersonetoanother,andhaveworkedparticularlyhardontheindex
by which every reference to a particular subject can be traced.
Thebookisnotwrittenforanuninformedreaderandindeedtheapproach
we have used is inappropriate for those coming to the topic of brewing for
the first time. We presume a good deal of knowledge about brewing be-
cause our objective is not to teach the fundamentals. For that, a book such
asBrewingbyLewisandYoung(thispublisher)wouldmakeagoodprimer.
Althoughwehaveincorporatedthelatestideasfrompublishedresearchand
from conversations with researchers and practical brewers alike, we have
not peppered the text with references to the original literature; such refer-
encestendto“date”atextquickly,yetanindividualresearchpaperusually
contains such a small kernel of new information that it only makes sense
or has relevance when subsumed into the vast storehouse of knowledge
thatbrewershaveaccumulatedoverdecadesandevencenturies.Neverthe-
less,amostinclusivetomesuchasBrewingScienceandPracticebyBriggs,
Boulton,BrookesandStevens(WoodheadPublishingLtd.,Cambridge)uses
references to the original literature and crucially provides an entre´e to that
source of information for those who need it.
Towriteabookthatisreasonablyshortonsuchavastsubjectasmalting
and brewing demands that we make decisions about what to include or
excludeandthelevelofdetailthatisappropriateineachchapter.Giventhat
each chapter was originally intended to be called an essay and to be about
1000wordsinlength,ourpredilectionhasbeentoerronthesideofbrevity.
Wearesurewewillnotmeettherequirementsofeveryreaderineverycase.
For example, we have made few comments about health issues related to
beerthoughthesehaveincreasinglyinterestedtheindustry;theseminaltext
in this field is Beer:HealthandNutrition by Bamforth (Blackwell, Oxford))
after which there is very little else to say.
Writingthisbookhastakenagooddealoftimeandarriveswellafterthe
date originally promised to the publisher. We therefore thank Susan Safren
who chased us relentlessly to complete the book especially when lots of
other projects and activities seemed more attractive or more urgent. For
the same reason we heartily thank the extraordinarily patient and talented
women, whom we were smart enough to marry, for doing all the things
they do that made this book possible.
Contents
I Qualities
1. Proteins............................................................................ 3
2. pH................................................................................... 13
3. Color................................................................................ 20
4. Foam................................................................................ 28
5. Haze................................................................................ 43
6. Microbiology...................................................................... 58
7. Inorganic Ions.................................................................... 69
II Processes
8. Raw Materials..................................................................... 77
9. Modification....................................................................... 93
10. Enzymes........................................................................... 105
vii
viii Contents
11. Yeast................................................................................ 114
12. Oxygen............................................................................. 131
13. Water and Energy............................................................... 143
14. Sanitation and Quality......................................................... 161
Index..................................................................................... 171
I
Qualities
1
Proteins
Proteins primarily enter the brewing process from barley by way of malt.
The bulk of this protein resides within the cells of the endosperm of barley
grains where, by the time of grain maturity, the protein forms a matrix
in which the large and small starch granules are embedded. There is also
some protein in the endosperm cell walls, primarily in the middle lamella
thatformstheintersectionbetweenadjacentcells.Also,thereisanintensely
hydrophobicproteinparticle(hydrophobin)presentinbarleyscontaminated
with mold spores (notably, Fusarium) that induces gushing of beer and the
factor in malt responsible for premature yeast flocculation is proteinaceous
in character.
A classical measure of protein is the nitrogen content of grain, which
is measured by the Kjeldahl method. The grain is digested completely by
boiling sulfuric acid plus catalysts and the ammonium ion, so formed from
all the nitrogen-containing substances in the sample, is quantified. Alterna-
tively, the Dumas method can be used, in which the sample is gasified by
incinerationinoxygentoformoxidesofnitrogen;byreduction,thenitrogen
gas formed can be measured. In either case the factor 6.25 is then applied
to convert total nitrogen to total protein because, on average, proteins con-
tain 16% nitrogen. Because there are many compounds in barley and malt
that contain nitrogen but are not proteins, the “protein” value, calculated
in this way, is spuriously high and the factor 5.7 is sometimes preferred.
3
4 Chapter1
Nevertheless, protein values based on this admittedly false premise com-
priseaveryusefulandpracticalguidefortheevaluationofbarleyandmalt.
Proteins can also be measured in aqueous samples (wort and beer) by the
useofCoomasieBrilliantBlue,adyethatreactswithproteins;analystsread
the color formed in a spectrophotometer. Values are always much smaller
than the Kjeldahl values for the same samples because the dye is blind to
small nitrogen-containing molecules.
Measurement of N-Containing Materials in Brewing
Oneofthemostchallengingmaterialstomeasureinbeeranditsrawma-
terials is protein. This is primarily on account of the heterogeneity of the
speciesthatareinvolved.Whereascomponentssuchasβ-glucanandstarch
have a single unit building block (glucose), there are 20 or more different
monomericunitsthatcompriseproteins,namelytheaminoacids.Whereas
themeasurementofthesebuildingblocksisstraightforward(theyreactas
a group with ninhydrin to afford a violet color and can even be measured
individuallyafterfractionatingbycolumnchromatography),whentheyen-
ter into peptide bond formation to produce ever increasing complexities
of peptides, polypeptides and proteins, there is a tremendous diversity of
species.Simplealgebrawillillustratejusthowmanypermutationsofdipep-
tide can be constructed from just two different amino acids (20 different
aminoacidsinallmannerofpermutations,withaminoacid1providingits
–CO H group to the peptide bond in one set but its –NH group in the
2 2
other,e.g.,Glycyl-alanineandAlanyl-glycinearedifferentdipeptides.)Going
successivelytotripeptidesrightthewaythroughpolypeptidescomplicates
thesituationexponentially.
Onewaytoobtainareadingfortotalpeptidesandpolypeptideswouldbe
tototallyhydrolyzethemixture,sayasfoundinbarley,malt,wortorbeer,
and measure the amino acids released. This is seldom efficient, including
fromatimeperspective.Oneofthemosttime-reveredapproacheshasbeen
thatofKjeldahl,whereinthetotalityofnitrogenousmaterialsisconverted
to ammonia by digestion, and the ammonia measured colorimetrically. As
nitrogenconstitutessome16%ofthetotalweightofaprotein,thevaluefor
N obtained was traditionally multiplied by 6.25 to arrive at an estimation
of protein. This method has now been superseded for safety reasons by
theDumasmethodinwhichthereistotalcombustionofproteinpriorto
assessmentofnitrogen.Thisgivesevenhigherapparentlevelsforprotein,
becauseofthemorecomprehensivedigestion,butthisonlyillustratesthe