Characteristics of African traditional beers … of African traditional beers brewed with sorghum...

BASE Biotechnol. Agron. Soc. Environ.201216(4),509-530 Focus on:

CharacteristicsofAfricantraditionalbeersbrewedwithsorghummalt:areviewFrançoisLyumugabe(1,3),JacquesGros(2),JohnNzungize(4),EmmanuelBajyana(3),PhilippeThonart(1)(1)Univ.Liege-GemblouxAgro-BioTech.WalloonCentreofIndustrialBiology(CWBI).UnitofBio-Industry.PassagedesDéportés,2.B-5030Gembloux(Belgium).E-mail:[email protected](2)UniversitéCatholiquedeLouvain.EarthandLifeInstitute(ELIM).UnitofBreweryandFoodIndustries.CroixduSud,2Bte7.B-1348Louvain-la-Neuve(Belgium).(3)NationalUniversityofRwanda.FacultyofSciences.UnitofBiotechnologies.BP117.RWA-Butare(Rwanda).(4)InstitutdesSciencesAgronomiquesduRwanda(ISAR).RueDéputéKamuzinziKiyovu,47.BP5016.RWA-Kigali(Rwanda).

ReceivedonSeptember13,2011;acceptedonAugust6,2012.

TraditionalsorghumbeersareproducedinseveralcountriesofAfrica,butvariationsinthemanufacturingprocessmayoccurdependingonthegeographiclocalization.Thesebeersareveryrichincalories,B-groupvitaminsincludingthiamine,folicacid,riboflavinandnicotinicacid,andessentialaminoacidssuchaslysine.However, thetraditionalsorghumbeeris lessattractivethanWesternbeersbecauseofitspoorerhygienicquality,organolepticvariationsandshortershelflife.Researchinto themicrobiological and biochemical characteristics of traditional sorghum beers as well as their technologies havebeenperformedanddocumentedinseveralAfricancountries.ThisreviewaimstosummarizetheproductionprocessesandcompositionalcharacteristicsofAfricantraditionalsorghumbeers(ikigage,merissa,doro,dolo,pito,amgbaandtchoukoutou).Italsohighlightsthemajordifferencesbetweenthesetraditionalbeersandbarleymaltbeer,consumedworldwide,andsuggestsadaptationsthatcouldbemadetoimprovetheproductionprocessoftraditionalsorghumbeer.Keywords. Cereals,sugar, fermentation,malt,sorghumgrain,beers,grain,barley,foods,Africa.

Caractéristiques des bières traditionnelles africaines brassées avec le malt de sorgho (synthèse bibliographique).Lesbièrestraditionnellesàbasedesorghosontproduitesdansplusieurspaysd’Afrique,maislesprocessusdefabricationvarienten fonctionde leur localisationgéographique.Elles sont très richesencalories, envitaminesdugroupeBcomprenant lathiamine,l’acidefolique,lariboflavineetl’acidenicotinique,etenacidesaminésessentielstelsquelalysine.Cependant,lesbièresafricainesàbasedesorghosontmoinsattrayantesquelesbièresoccidentalesenraisondeleurqualitéhygiénique,delavariationdeleurscaractéristiquesorganoleptiquesetdeleurcourteduréedeconservation.Lesrecherchessurlescaractéristiquesmicrobiologiques,biochimiquesettechnologiquesdesbièrestraditionnellesafricainesontétéeffectuéesetdocumentéesdansplusieurs pays d’Afrique. L’objectif de cette revue bibliographique sur les bières traditionnelles à base de sorgho est derécapitulerleprocessusdefabricationetlescaractéristiquesdesbièrestraditionnellesafricaines(ikigage,merissa,doro,dolo,pito,amgbaettchoukoutou)àbasedesorgho,toutenprécisantlesdifférencesmajeuresaveclabièreàbasedemaltd’orge.Cetterevues’adapteégalementauprogrèsaccomplidansl’améliorationdesbièrestraditionnellesafricainesàbasedesorgho.Mots-clés. Céréale, sucre, fermentation,malt,sorgho,fermentation,bière,grain,orge,produitalimentaire,Afrique.

1. INTRODUCTION

Sorghum,unlikebarley,isverywelladaptedtothesemi-aridandsub-tropicalconditionsprevailingovermostoftheAfricancontinent(Aguetal.,1998).Likebarley,sorghumbelongstothegrassfamilyofGramineae.InAfrica, sorghum grain is themajor cereal crop usedto produce the traditional “opaque” beers (Novellie,

1976;Asiedu,1991).However,onlycertainsorghumvarieties(e.g.redgrain)arespecificallyusedtoproducesorghumbeers.Thesebeers are knownas ikigage inRwanda (Lyumugabe etal., 2010), tchoukoutou inBeninandTogo(Kayodéetal.,2005),doloinBurkina-Faso(Dickoetal.,2006),pitoorburkutuinNigeriaandGhana(Ekundayo,1969;Faparusietal.,1973),amgbain Cameroon (Chevassus-Agnes et al., 1979), doro

510 Biotechnol. Agron. Soc. Environ. 201216(4),509-530 LyumugabeF.,GrosJ.,NzungizeJ.etal.

orchibuku inZimbabwe (Chamunorwa etal., 2002),merissa in Sudan (Dirar, 1978),mtama in Tanzania(Tisekwa,1989),bili biliinChad(Maouraetal.,2005)andkaffirinSouthAfrica(Novellieetal.,1986).

ThemanufacturingprocessesofAfricantraditionalsorghum beer essentially involves malting, drying,milling, souring, boiling, mashing and alcoholicfermentation,butvariationsmayoccurdependingonthe geographic localization (Haggblade et al., 2004).These types of beer differ from European (lager)types in the fact that lactic fermentation also occursduringsorghumbeerprocessing. Inaddition,Africantraditionalsorghumbeer isconsumedwhile it is stillfermenting, and the drink contains large amounts offragmentsofinsolublematerials(Rooneyetal.,1991).Thesefragmentsaremainlystarchresiduesanddextrinsthatarenotdigestedduringmashingandfermentation(Glennieetal.,1986).SorghumbeersbearverylittleresemblanceinappearancetoWesternbeermadewithbarley.However,somestudieshavesuggestedthattheuseofsorghummalt(insteadofbarleymalt)inlager-beerbrewing isunlikely tosucceedbecauseofsomeinherent problems (enzymes, starch characteristics,polyphenols)associatedwithsorghum(Aisien,1982;Palmer,1991;Bajomoetal.,1994).

Several studies into the microbiological andbiochemical characteristics of traditional sorghumbeersaswellas their technologieshavebeencarriedout and documented in different African countries(Novellie, 1962; Ekundayo, 1969; Faparusi et al.,1973;Dirar,1978;Tisekwa,1989;Chamunorwaetal.,2002;Maoura et al., 2005).A very varied yeast andlactic bacteria acid flora has been found inAfricansorghumbeers,althoughSaccharomyces cerevisiaeandheterofermentativeLactobacillususuallypredominate(Novellie,1976;Sefa-dedehetal.,1999;Chamunorwaet al., 2002; Maoura et al., 2005; Kayodé et al.,2007a; Lyumugabe et al., 2010). TraditionalAfricansorghum beers are very rich in calories, B-groupvitamins including thiamine, folic acid, riboflavin,andnicotinicacid,andessentialaminoacidssuchaslysin (Chevassus-Agnes et al., 1979). The beers areconsumedatvariousfestivalsandAfricanceremonies(e.g.,marriage,birth,baptism, thehandingoverof adowry,etc.)andconstituteasourceofeconomicreturnforthefemalebeerproducers.However,inthemajorityofAfricancountries,traditionalsorghumbeersarelessattractivethanWesternbeersbrewedwithbarleymaltbecause of their poor hygienic quality, low ethanolcontent, organoleptic variation and unsatisfactoryconservation (Novellie et al., 1986; Tisekwa, 1989;Sanni et al., 1999; Lyumugabe et al., 2010). Thisreview aims to summarize the production processesand characteristics of African traditional sorghumbeers.Italsohighlightsthemajordifferencesbetweenthesetraditionalbeersandthefamiliarbarleymaltbeer,

consumed worldwide, and suggests adaptations thatcouldbemadetoimprovetheproductionprocessesoftraditionalsorghumbeer.

2. MALTING

Malting is the germination of cereal grain in moistairundercontrolledconditions,theprimaryobjectivebeing to promote the development of hydrolyticenzymes,which are not present in the ungerminatedgrain. The malting process essentially involvessteeping, germinating and limiting cereal seedlinggrowth, once enzymes have been produced for thedegradationofstarchandproteinsinthecerealgrain,butbeforetheexhaustionofthepolysaccharide.

2.1. Steeping

The steeping or soaking of cereal grain in water iswidelyacknowledgedasthemostcriticalstageofthemalting process (French et al., 1990; Dewar etal.,1997). This is a consequence of the importance ofinitiating germination such that modification of theendospermstructurewillprogressatarateproducingmaltof thedesiredquality.DuringtheWesternbeersbrewing process (Figure 1),malting beginswith thesoakingofthebarleyinwaterfor2daysat10-16°Cin order to increase the moisture content to around45% (Moll, 1991;Waites et al., 2001). Periodically,the water is temporarily drained off and aeration isprovided,thuspreventinganaerobicconditionsthatcancausegrainembryodamage.InAfrica,thetraditionalsorghummaltingprocessalsostartswith thesoakingofthesorghumgraininwaterfor10to24hatambienttemperature (Maoura et al., 2009;Lyumugabe et al.,2010), but, in this case, thewater is not renewed oraired.Thesteep-outmoisturecontentofsorghumgrainis affected by both steeping time and temperature(Dewaretal.,1997).However,thesteepingperiodatagiventimevariesaccordingtothesorghumcultivar.Avariationinmoisturecontentof32.4 to43.4%hasbeen observed after steeping 26sorghum cultivarsfor 24h (Kumar et al., 1992). The steep moistureincreases as the steeping temperature rises from 10to30°C, for anygivenperiod (Novellie,1962).Theeffect of steeping conditions has been extensivelyinvestigated in an attempt to increase sorghummaltamylase activity. In 1962, Novellie reported thatsteeping time had little effect on the final diastaticpowerofsorghummalt.Steepmoistureof42to48%,attainedaftersteepingsorghumfor18to22hat30°C,isoptimalforenzymaticactivity(Moralletal.,1986).An increase in steep moisture with a steeping timeof between 12 and 20h at 30°C is accompanied bya corresponding increase in reducing sugar content,

Africantraditionalsorghumbeer 511

and in cold-and hot water extracts (Owuama et al.,1994).The level of increase in these features of thesorghummalt appears to be directly proportional toitsdiastaticpower(Pathiranaetal.,1983).Asteepingregime,andinparticulartheuseofair-restsandafinalwarmwater (40°C) steepingperiodhasbeen showntoenhancesorghummaltquality,includingβ-amylaseactivity(Ezeoguetal.,1995).Alaterstudyspecificallyconfirmed the importance of the effect of air-restson the level of sorghum malt β-amylase activity(Okungbowaetal.,2002).Itislikelythatthepresenceofoxygen leads toamore rapid increase in seedlingmetabolicactivity (Dewaretal.,1997).Thediastaticpower ofmalt has also been shown to increasewithsteeping temperature (up 30°C) and with the levelof free amino nitrogen (FAN) (Dewar et al., 1997).Steeping the sorghum grain in dilute alkaline liquor(0.1%ofCa(OH)2,KOHorNaOH)hasbeenshowntosignificantlyenhancethediastaticactivityofsorghummaltespeciallyβ-amylaseactivity(Okoloetal.,1996;Okungbowaetal.,2002).

2.2. Germination

After steeping, the sorghum grains are then spreadout on a germination device (e.g. green plantainleaves or a plastic sheet) to form a layer (2 to 3cmin thickness) and the grains are kept covered for2-3days at ambient temperature (Chevassus-Agneset al., 1979; Lyumugabe et al., 2010). The layer ofgrains is sometimes turnedover twice a day and theinitialmoisture level ismaintained by sprayingwithwater.Thistechniqueissimilartotheoldgerminationprocess thatwaspreviouslyused toproduceWesternbeers,wherebarleygrainswerespreadoutonmaltingfloorstoadepthof10-20cmfor3-5daysat16-19°C(Moll, 1991). However,Western breweries now usevariousmechanizedsystems,whichhavegrainbedsofabout1mindepth.Thesegrainsbedsareaeratedwithmoistcoolairandturnedmechanicallyevery8-12htoaid respirationby thegrainand toprevent thebuild-upof heat; otherwise thegrain embryomaybecomedamaged.

Figure 1. BrewingprocessofWesternbeers—Procédé de brassage des bières occidentales(Moll,1991;Waitesetal.,2001).

Malting Barley grains

Germinationvessel

Adjunctcooker

Steeptank

MaltstoreKiln

Mash tun

Lauter tun or filter press

Mill

Copper

Maturation tank

Clarification Sterile filtration or pasteurization

Packaging (bottles, cans, kegs and tanks)

Whirlpool

Plate heat exchangersSelected yeast store

Fermenter (cylindroconical or traditional)

Mashing

Filtration

Wort boiling

Fermentation

Beer

Maturation

Filtration and sterilization

Wort treatment(cooling)

Starch adjuncts

Spent grains

Hops


Germinationinvolvestheoutgrowthoftheplumuleand radicle of the seedling until suitable enzymes(e.g. starch degrading enzymes and proteases) havebeen produced for the malt (Palmer, 1989). Duringgermination, the hormone gibberellic acid (GA), atlow concentration (0.1-0.2ppm), induces the barleyaleurone layer to produce endosperm-degradingenzymessuchasα-amylase,protease,pentosanasesandendo-beta-glucanase(Palmer,1989),butthishormoneplaysnosuchroleinenzymedevelopmentinsorghum(Aisien et al., 1983; Palmer, 1989). In sorghum,α-amylaseandcarboxypeptidasesareproducedbythescutellum, while endo-β-glucanase, limit dextrinaseandendo-proteasedevelopin thestarchyendosperm.Thesecontrastswithmaltingbarleywhereα-amylase,endo-protease, limitdextrinaseandendo-β-glucanasedevelopinthealeuronelayer,whilecarboxypeptidasesand β-amylase are found in the starchy endosperm(Aisien et al., 1983; Palmer, 1989). Phosphate, animportant mineral found in barley aleurone tissueand in the sorghum embryo (Palmer et al., 1989),mayaccountfordifferencesintheenzyme-producingpotentials of the barley aleurone and the sorghumembryo(Aguetal.,1998).Theendospermofmaltedsorghumretainsstarchcompactionandisnotasfriableasthebarleymaltgrain.Malting(respirationandroot)lossofsorghummaltsisabout20%,whilethemaltinglossofbarleymaltisabout7%after6dofgrowthat25°Cand16°C(Palmeretal.,1989).

Anotherimportantphysiologicaldifferencebetweensorghum and barley malts is that malted sorghumgrains contain low levels of endo-β-glucanase andβ-amylase(Aisienetal.,1983).Intheirexperiments,Beta et al. (1995) found that levels of α-amylaseactivity (25-183U.g-1) and β-amylase activity (11-41SDU.g-1) in sorghum malt varied, depending onthe sorghum variety. Recently, a comparative studyofwhite sorghum varieties indicated that the F-2-20varietiesfromSenegalhaveanα-amylaseactivityof312, 6U.g-1 and a β-amylase activity of 62, 7U.g-1(Khady et al., 2010). However, compared to barleymalt, whose β-amylase activity is 400U.g-1 (Tayloretal.,1993),sorghummalt isnotadaptedtobeusedinanefficientbrewing industry.Severalassumptionsexplaintheweaknessofβ-amylaseactivityinsorghummalt. Uriyo et al. (1999) explained this weaknessin terms of an interaction between β-amylase andpolyphenols during the extraction process, whereasDufour et al. (1992) showed that β-amylase activityremains weak, even in sorghum varieties with lowpolyphenolcontent.Otherauthorsclaimthatinhibitorsapart from polyphenols would be present, causingpartial solubilization of β-amylase or a weak outputduringmalting(Palmeretal.,1989;Aguetal.,1997a).According to Taylor et al. (1993), ungerminatedsorghum also does not exhibit β-amylase activity.

Thisisfundamentallydifferentfrombarley,wheretheungerminatedgraindoesexhibitβ-amylaseactivity.Itappearsthattropicalcerealgrainssuchaspearlmillet,sorghumandmaizepossessonlythe“ubiquitous”formofβ-amylase,whereastemperateTriticeaecerealssuchasbarley,wheatandryealsopossessthe“endospermspecific”formoftheenzyme,whichispresentinthesegrainsatseedmaturity(Zeigler,1999).

Germination of sorghum grains at a temperatureof between 25 and 30°C is recommended for thedevelopmentofoptimumamylaseanddiastaticpowerinsorghummalt(Novellie,1962;Okaforetal.,1980).At 30°C, 3 to 7days of sorghum grain germinationproduces well modified malts with a high diastaticpower,andanincreaselevelofhot-waterextract,sugarcontentandfreeaminonitrogen(Morralletal.,1986;Lasekan et al., 1995), but the optimal germinationtime and temperature varywith the sorghum variety(Novellie,1962;Okaforetal.,1980;Demuyakoretal.,1992).Activityofα-amylaseandβ-amylasehasbeenshown to develop to a greater extend in the yellowand red sorghum varieties than in white sorghumvarietieswhengerminatedat30°C(Aguetal.,1997b).However,germinatingsorghumat the relativelyhightemperature of 35°C or at lower temperatures ofbetween15and20°C,slowsdownamylaseformationand consequently reduces diastatic power (Morrallet al., 1986).Moreover, germinating sorghum grainsheavilyinfectedwithmouldsproduceamaltwithlowamylaseactivity(Aguetal.,1999).Microbialinfectionof Nigerian sorghum grain has been shown to becausedbythepresenceofAspergillussp.,Penicilliumsp., Neurospora sp., Rhizopus sp., Fusarium sp.,Curvularia sp. and Dreschlera sp. (Boboye et al.,1994). Formaldehyde (0.1%) can be added to thesteep to retard fungal activity (Palmer et al., 1989).As a result of fungal grain infection, someAfricantraditionalopaquebeershavebeenreportedtocontaindifferentamountsofaflatoxins(Nikanderetal.,1991).Recently,studiescarriedoutbyMatumbaetal.(2011)indicatethepresenceofaflatoxin(6,6to54,6µg.kg-1)inasorghummaltfromMalawi.

Maltase, or α-glucosidase, which catalysesthe hydrolysis of maltose into glucose, is presentin ungerminated sorghum and does not increasesignificantly during malting. Sorghum maltase is averyheavymolecularweightenzyme,whosesolubilitycharacteristics differ from those of barley. Sorghumα-glucosidaseissolubleinwater,butisalsoactiveinitsinsolublestateandadheresstronglytoinsolublesolids(Novellie,1982;Tayloretal.,1994).Thedevelopmentofα-glucosidaseinsorghumisinfluencedbylengthofgerminationperiodandtemperature(Aguetal.,1997a).Inbarley,α-glucosidaselevelsaregenerallylowerthanthoseofsorghummalt,especiallyat30°Candatday5ofgermination(Aguetal.,1997c).Thesorghummalt


withthehighestmaltaseactivity,however,producesthelowestglucoselevelsinwort,suggestingthatmaltaseisnotthedominantenzymeproducingsugarduringthemashingofsorghummalts(Aguetal.,1997a).

2.3. Kilning

Kilninginvolvesthedryingofthegreenmaltinakilnorovenatarelativelyhightemperatureuntiltherootletsbecomefriableorbrittle.Kilninghastheobjectiveofstopping embryo growth and enzyme activity, whileminimizing enzyme denaturation, and the processdevelopsflavorandcolor(melanoidincompounds).IntheAfricantraditionalsorghumbeerbrewingprocess,the germinated sorghum grains are dried under thesun and are stored under protection during the nighttoavoidrehydration.Generally,thisdryingsteptakes2-3days depending on sunlight intensity. However,in theWesternbeer brewingprocess, thegerminatedbarleygrainsarekilnedviaa two-stageprocess.Thegrain are first of all dried at 50-60°C and are thencuredat80-110°C(Moll,1991).

Aspartof thesorghummaltingprocess,Novellie(1962)advocatedthekilningofthemaltupto50°C.However,whilstkilningperiodsat80°Cmayenhancetheflavorofthemalt,suchatemperaturemaydamagetheenzymaticactivityofthemalt(Aisienetal.,1987)andreducevolatilecompounds.Kilningmaltsintwostages,initiallyto55°Candsubsequentlyto65°C,hasbeenshowntoproducegoodmaltswithaconsiderablereductioninmoistureandahighersugarcontentthankilningatasingletemperatureof65°C(Owuamaetal.,1994).Thus,thetwo-stagekilningprocessallowsforthegreatersurvivalofhydrolyticenzymesandforthemalttoacquireitscharacteristicflavor.

3. MASHING

Theobjectivesofmashingaretoformandextractintosolution, fermentable sugars, amino acids, vitamins,etc., frommalt.Malt normally providesmost of thepotentialfermentablematerialsandsufficientenzymesto generate a well balanced fermentation medium.Africansorghumbeerisuniqueasafermentedbeverageinrequiringstarch,notonlyasasourceofsugar,butasathickeningandsuspendingagent.Gelatinizedstarchgivesthebeeritscharacteristiccreamybodyandkeepsinsuspension theparticlesofgrainandmalt thatareessentialconstituentsofbeer.

One of the problems involved in sorghum beerbrewingistheefficientconversionofthestarchextractsinto fermentable sugars for yeast (Saccharomyces cerevisiae). Regarding the relative amounts offermentable sugars in sorghum and barley worts,themajor difference has been found to reside in the

glucose content (Palmer, 1989;Dufour et al., 1992).While some studieshave foundbarleymaltworts tocontainmoremaltosethanglucose(Briggsetal.,1981;Dufouretal.,1992),othershavereportedthatsorghummalt worts contain similar levels of glucose andmaltose(Taylor,1992).Thedifferenceobservedintheproportionsofglucoseandmaltosesugarsinsorghumandbarleymaltwortshasbeenattributed to the lowlevelsofβ-amylase insorghummalt (Palmer,1989).Other authors (Taylor et al., 1994) have attributedthehighlevelofglucosefoundinsorghummaltwortto the catalytic activity of α-glucosidase, from themaltase family, in hydrolysing maltose into glucosein sorghummalt wort. However,Agu et al. (1997c)showedthatthereisnodirectrelationshipbetweentheα-glucosidase levels in sorghum or barley malt andthemaltosetoglucoseratiosfoundintheirworts.Itisworthnotingthat,inthatstudy,barleymaltdevelopeda higher level of α-glucosidase than did sorghummalt, but that it produced less glucose and severaltimesmoremaltoseinthewortthanitwasthecaseinsorghumwort.Themain reason for the limitationofmaltoseproductioninsorghummaltwortislikelytobeinadequategelatinizationofsorghumstarchratherthaninadequatelevelsofhydrolyticenzymes(Dufouretal.,1992; Agu et al., 1997c). Results obtained by Aguetal.(1997b)showedthatdifferentsorghumvarietiesmaltedandmashedundersimilarconditionspresentedwidevariationsintheirsugarprofilesduetoseasonalandprocessingdifferences.For example, the authorsshowed that, when malt is produced at 30°C, thewhite(ISCV400)andyellow(SS20)sorghumvarietiesproduce high glucose andmaltose levels,while SS9(red variety) and SS16 (white variety) produce lowglucose and higher maltose levels. However, theselasttwovarietiesproducehigherlevelsofglucoseandmaltose when malt is produced at 20°C. However,the variations caused by seed variety and maltingtemperaturedonotalter thegreater influenceexertedbystarchgelatinizationonthesugarprofileofsorghumworts thanon the sugarprofileofbarleyworts (Aguetal.,1998).

Generally, sorghum starch gelatinizationtemperatures(67-81°C)arefarhigher(Akingbalaetal.,1982;Betaetal.,2001)thantherangequotedforbarleystarch of 51-60°C (Lineback, 1984). Furthermore,these temperatures increase the thermal deactivationof the sorghum malt enzyme (Guerra et al., 2009).Consequently, the simultaneous gelatinization andhydrolysisofstarch,whichoccursduringmashingofthebarleymalt,isproblematicalinthecaseofsorghummalt.Althoughshortmashing(gelatinization)periodsat 75°C followed by a conversion (saccharification)period at 65°C would improve the development ofextractsfromsorghummalt,unacceptableextractlosswouldstilloccurbecauseofenzymeinactivationand


inadequategelatinization(Palmeretal.,1989).Indeed,relativelyhighlevelsofstarchextractcomparabletothoseofbarleymaltshavebeenobtainedbyusinganon-conventionalmashingprocedure.Theprocedureinvolves,decantingactiveenzymewortaftermashingsorghummalt at 45°C for 30min, and gelatinizingthestarchygristresidueat80to100°Cbeforemixingwiththewort,toachieveasaccharifyingtemperatureof 63-65°C (Palmer, 1989; Igyor et al., 2001).Theviscositiesofsorghummaltwortshavebeenshowntobesimilartothoseofbarleymalts(Igyoretal.,2001),but the fermentableextractsof thesesorghumwortshavebeenshowntobestilllowerthanthoseofbarleymalt(Palmer,1989).Theseresultssuggestthatsmallquantities ofβ-amylase in sorghumwort also affectsaccharification.

The drawbacks highlighted above in usingsorghum malt in beer brewing led to the approachproposing the use of mixtures of malted barley(30-40%) with sorghum (60-70%) during mashing(Okafor et al., 1980; Goode et al., 2003), or theaddition of exogenous enzymes to the unmaltedsorghum (Dale et al., 1989; Bajomo et al., 1994).In this last case, the addition of external enzymesis associated with processing difficulties such asα-aminonitrogen(FAN)depletion(Daleetal.,1989).The advantage of including a percentage of maltedsorghum as a source of endogenous proteases hasalsobeen reported.Theadditionofmalted sorghumavoids the need to add these enzymes, therebyavoiding the poor foam retention associated withcommercial proteolytic enzymes (Agu et al., 1998).However, these optimal solutions for reducing thelevels of non-fermentable sugars in sorghum wortsare inappropriate in an African traditional brewingcontextbecausethetropicalclimateisnotconducivetobarleycultivation,andcommercialenzymesareveryexpensive. Nevertheless, a 20% (w/v) sweet potatoflour substitution for sorghummalt has been shownto increase the level of β-amylase in sorghumwort(Etimetal.,1992).Pearlmillet(Pennisetum glaucum)maltalsoappearstohavesomeadvantagescomparedtosorghumasithasahigherβ-amylaseactivityandhigherFANlevels(Pelembeetal.,2004).InRwandantraditionalsorghumbeerbrewing, theassociationofsorghummaltandEleusine coracana (uburo)or theaddition of banana juice (umutobe) during sorghummalt mashing increases the fermentable sugars insorghumwort(Lyumugabeetal.,2010).Asβ-amylaseistheenzymeresponsibleforthehydrolysisofstarchintomaltose,thehighlevelofactivityofthisenzymeinEleusine coracana malt compared with sorghummalt (Taylor, 2009) could explain the increase infermentable sugars in this wort. However, brewingprocesses using a mixture of sorghum with localcultureshavenotbeenextensivelyinvestigated.

Generally,aftermashing,themashisfilteredbeforeboiling.During theAfrican traditionalbeerbrewingprocess, filtration is achievedby simple decantation(Lyumugabe et al., 2010) or via a rudimentarypress filter made of a nylon cloth stretched over abowlandrakedwithawoodenstick (Maouraetal.,2009). In comparison with barley, sorghum maltmashes filter poorly (Aisien et al., 1987). This isclearly related to differences in the qualities of theendospermcellwallsofsorghumandbarley.Unlikeinbarley,theendospermcellwallsinsorghumarenotsubstantially broken down duringmalting (Glennie,1984). The cell walls themselves are rich in water-unextractable glucoronoarabinoxylans (Verbruggen,1996) and sorghum malt appears to be deficient inthewalldegradingenzymeendo-β-glucanase(Aisienetal., 1983).This seems to pose a serious filtrationproblemforsorghummaltmashes,andtheadditionofexogenoushemicellulolyticenzymesisprobablyonlyashort-termsolution.

Boilingofwort isperformedforseveralreasons,inparticular tobringabout thedenaturationofmaltenzymes and any enzymes supplements, and thesterilizationofthewort.AlthoughthisstageexistsinthebrewingprocessofmanyAfricantraditionalsorghumbeers (e.g. dolo, tchoukoutou, amgba) (Chevassus-Agnes et al., 1979; Dicko et al., 2006; Kayodé etal., 2007b), it is absent from the brewing processof traditional sorghum beers (e.g. ikigage, mtama,impeke)fromEastAfricancountries(Tisekwa,1989;Nzigamasabo et al., 2009;Lyumugabe etal., 2010).In the European beer brewing process, barley wortobtained from themash is transferred to a “copper”(“kettle”) for boiling, alongwith dried hops or hopextracts.Hopsaretheflowerconesofthefemalehopvine (Humulus lupulus), and they contain α and βacids,primarilyhumulonesandlupulones.Thesegivetobeeritsbitterflavor,afterisomerizationofα-acidsinto iso-α acids during boiling, and they also helpinhibit certain beer spoilage bacteria and maintainfoam stability. African traditional sorghum beersare generally unhopped. However, several studieshavereported thepossibilityofusingAfricanplants(e.g.Vernonia amygdalina,Gongronema latifolium,Garcinia kola) instead of hops inAfrican sorghumbeers (Ogundiwin et al., 1991; Okoh et al., 1995;Ajebesoneetal.,2004;Okoroetal.,2007;Adenugaetal.,2010)becausethehopplantisatemperatecropand cannot be successfully grown inAfrica tropicalcountries. Vernonia amygdalina, known as “bitterleaf”,canbeusedinstead,becauseitresembleshopsin its antimicrobial properties (Mboto et al., 2009;Obohetal.,2009)andbitterflavor(Ajebesoneetal.,2004;Adenugaetal.,2010).Furthermoretheadditionof extract of V. amygdalina leaves to sorghumwort increases the levels of amino acids, mainly


isoleucine, leucine and histidine (Lasekan et al.,1999).However,furtherresearchneedstobedirectedinparticulartowardsthecontributionofthisplanttotheorganolepticpropertiesofsorghumbeer.

4. FERMENTATION

Fermentation is the important step by which yeastconverts the sugars in the wort into ethyl alcohol.In Western breweries, the fermentation process isstarted by selected yeast strains (S. cerevisae orS. carlsbergensis) and the fermentation time rangesbetween 8-15days at 10-16°C (Moll, 1991;Waitesetal.,2001).InthecaseofAfricantraditionalsorghumbeers, sorghumwort is inoculatedwith a traditionalleaven,andfermentationtimevariesbetween10and24hinambienttemperature.

African traditional leaven is a result of thespontaneous fermentation of sorghum malt wort(Kayodé et al., 2005;Lyumugabe et al., 2010).Themanufacturingmethodsof this leavenarediverse inAfrica and depend on built-in ingredients. Table 1shows the types of microorganisms involved inspontaneous fermentation in traditional sorghumbeer brewing. Very varied yeasts and bacteriaflora have been found in African sorghum beers,although S. cerevisiae andLactobacillus sp. usuallypredominate (Novellie, 1976; Maoura et al., 2005;Kayodéetal.,2007a;Lyumugabeetal.,2010).UnlikeEuropean beer made with barley, African sorghumbeers are typical examples of lactic fermentationfollowedbyalcoholicfermentationinwhichinitially,lacticacidbacteria(LAB),andlateryeasts,playthedominant role (Novellie, 1982; Holzapfel, 1997;Kayodéetal.,2005;Maouraetal.,2009).Duetotheirhigher growth rate, bacteria typically dominate theearlystagesoffermentation.Asymbioticrelationshipcould explain the simultaneous presence of yeastsandLAB.LABcreateanacidenvironmentfavorableto the proliferation of yeasts. These yeasts producevitamins and increase other factors, such as aminoacids,toaidthegrowthofLAB.

UnlikeEuropean beers,where the desired flavoris often critically affected bywild yeasts and othermicroorganisms,African beers may display a widevariation in tastes and aromas while still beingacceptable to the consumer. As in the case of theBelgianbeer,Lambic,Africansorghumbeersaretheproduct of more or less spontaneous fermentation,in that pitching is not practiced.On theother hand,African sorghum beers differ from Lambic in thatthe Belgian beer is subjected to a very long post-fermentationperiodduringwhichyeastsofthegenusBrettanomycesareresponsibleforcreatingthetypicalbouquetofthatbeer(VanderWalt,1956).

5. TYPES OF AFRICAN TRADITIONAL SORGHUM BEER BREWING

Generally, African traditional sorghum beers arebrewed with pigmented sorghum varieties (red orbrown).Thewhitevarietiesarealwaysmixedwithredsorghum because consumers prefer to drink coloredbeerswhichtheybelievetobehealthy(Kayodéetal.,2005).TheseAfrican sorghum beers are not a clear,sparkling liquid, but opaque with suspended solids(5-7%).The beers have a rather low alcohol content(2-4.5%v/v),apHofbetween3.3and4andalacticacid rate of about 0.26%. Their color varies from apalebuff toapinkybrownaccording the ingredientsused.Usually,Africansorghumbeershaveatouchoffruitiness added to their fermentation odor.They arebeer isconsumed inanactively fermentingstateandtherefore their shelf life is a quite short (24h-72h)(Novellieet al.,1986;Tisekwa,1989;Maouraet al.,2009; Lyumugabe et al., 2010). However, Africantraditional sorghumbeersvary in their denominationand their production processes, according to theirgeographiclocalization.

5.1. Ikigage of Rwanda

Ikigageoramarwaisatraditionalalcoholicbeveragemanufactured in Rwanda with malted sorghum(Figure 2). The traditional process of ikigagemanufacture has been described by Lyumugabeet al. (2010).After washing, red sorghum grains areimmersedinwater(kwinika)for24h.Thegrainsarethendrainedinabagwithastonetopfor24hsothatthe process of germination is completed and grainrootlets appear (kumera). The grains are spread outonaclothinawetplace.Ashisspreadovertheclothandleavesoftheeucalyptusorbananatreearelaidontopoftheash.Thesorghumgrainsarethenspreadouton the leaves, to encourage germination. The grainsaredriedunderthesunforatleasttwodaysat29°C.Whenthegrainsaresemi-dry,therootletsareremoved(kuyavunga).Thesemi-drymaltgrainsaregroundorcrushed.Brewersheatwater(20l)toboilingandaddapproximately2kgofgroundmaltgrains inorder togelatinizethestarch.Thissolutionisthenmixedwithgroundmalt (16kg) ina largecontainer.Themixingtemperature is typically between 63°C and 71°C.Following the infusion process, cool water is added(40l)tobringthetemperaturebacktobetween34°Cand 40°C. In some cases, brewers leave a decanterof thismixture torest forapproximately3h inorderto eliminate the draffs (imvuzo). After cooling, thetraditionalleaven(umusemburo)isinoculatedinorderto start the fermentation process. The fermentationcontainer is covered with leaves of the banana tree,and then by a cloth and a lid. After 12 to 24h of


Table 1.MicroorganismsinvolvedinthefermentationofthemainAfricantraditionalsorghumbeers—Micro-organismes impliqués dans la fermentation de la plupart des bières traditionnelles africaines à base de sorgho.Beer name Predominant microorganisms involved Country ReferencesIkigage Saccharomyces cerevisiae

Issatchenkia orientalis Lactobacillus fermentumLactobacillus buchneriLactobacillus sp.

Rwanda Lyumugabeetal.,2010

Tchoukoutou SaccharomycescerevisiaeTorulaspora delbrueckiiSaccharomyces pastorianusLactobacillus divergensLactobacillus fermentumLactobacillus fructivorans Lactobacillus sp.

Benin Kayodéetal.,2005Kayodéetal.,2007

Bili bili or Amgba SaccharomycescerevisiaeKluyveromyces marxianusCryptococcus albidiusDebaryomyces hanseniLacticacidbacteria

Chad Maouraetal.,2005

Burkutu Saccharomyces cerevisiaeSaccharomyces chavelieriLeuconostoc mensenteroidesCandida acetobacter

NigeriaandGhana Blandinoetal.,2003VanderAaKühleetal.,2001

Pito SaccharomycescerevisiaeCandida tropicalisKloeckera apiculataHansenula anomala Torulaspora delbrueckii Schizosaccharomyces pombeKluyveromyces africanus Lactobacillus spp.Leuconostocspp.

Ghana Sefa-Dedehetal.,1999VanderAaKühleetal.,2001

Dolo Saccharomyces cerevisiaeLactobacillus delbrueckiiLactobacillus fermentum Pediococcus acidilactici Lactobacillus lactisLactococcus lactis

BurkinaFaso VanderAaKühleetal.,2001Sawadogo-Linganietal.,2007Gloveretal.,2009

Doro or Chibuku Saccharomyces cerevisiaeLactobacillus plantarum Lactobacillus delbrueckii Lactococcus lactisLactococcus raffinolactis

Zimbabwe Jespersen,2003Chamunorwaetal.,2002

Kaffir Saccharomyces cerevisiaeCandida kruseiKloeckera apiculataLactobacillus fermentumLactobacillus plantarumLactobacillus brevisLactococcus dextranicum

SouthernAfrica VanDerWalt,1956


fermentation, ikigage is ready for consumption. Theethanollevels,solubleproteinandthepHofikigageare2.2%(v/v),9.2g.l-1and3.9respectively(Lyumugabeetal.,2010).

5.2. Merissa of Sudan

Merissa is a traditional alcoholic beveragemanufactured inSudanusingmalted red sorghumormillet. Dirar (1978) describes a complex procedure(Figure 3)formakingmerissabeer.Theredsorghum

grains are malted, dried and reduced into flour.Ungerminatedsorghumismilledintoafineflourandcookedintwoequallots:thefirstlotislightlycookedtoagreyishbrownpastewhile,thesecondlotiswellcookedtoabrownpaste.Thesetwolotsarethenmixedandallowedtocool.Theresultingproduct,“futtara”,is agelatinized solidmaterial.Onepartmaltflour ismixed with a quantity of water necessary for goodhumidification and is incubated at room temperaturefor36huntillacticfermentationoccurs.Theacidpasteobtained(called“ajeen”)iscookedinacontainerand

Figure 2. Traditionalmanufacturingprocessesoftraditionalikigagebeer(adaptedfromLyumugabeetal.,2010)—Processus traditionnel de fabrication de la bière « ikigage » (adapté à partir de Lyumugabe et al., 2010).

Sorghum grains (Amakoma) Water (Amazi)

MixingGrinding

Warm water

Cool water

(40 l)Cooling (34 to 40 °C)

Decantation (3 h)Spent grains

(Imvuvu)

Ikigage beer

Leaven(Umusemburo)

Drying

(under sun, Kwanika, 48 to 72 h, 29°C)

Mashing

(infusion, 63 to 71 °C)

Fermentation

(± 28 °C, 72 h)

Fermentation

(± 28 °C, 24 h)

Fermentation

(± 30 °C, 12 or 24 h)

Malted sorghum (1 kg) and

roasted sorghum (0.5 kg)

Wort (Igikoma, 4 l)Steeping

(Kwinika, 24 h)

Germination

(Kumera, 24 h)

Fermentation

(± 28 °C, 24 or 48 h)

Cooking

(until evaporation ½)

Juice of Vernonia amygdalina

sheets (Umubirizi, ± 250 ml)

Malted sorghum (1 kg)


mashing is then carriedout until the substance takeson a chestnut color, with a high acidification and acaramelflavor.This product (called “soorij”) is thencooled.Malt(5%),waterandaninoculumofapreviousmerissa product are thenadded to the soorij and themixture is left to ferment for 4-5h. The resultingproduct(called“deboba”)isavigorouslyfermenting,thick,darksuspensionthat is toosourtodrink.Aftercooking,futtaraismixedwithabout5%maltflourandis successively added to thedeboba.After 8-10h offermentation,theproduct,merissa,isfilteredthrougha suitable fabric mesh to partially retain the solidparticles,whiletheliquidundergoesfullfermentation.TheresultingdrinkhasapHof4andanalcohollevelofaround5%(v/v).

5.3. Doro of Zimbabwe

The traditionalsorghumbeerofZimbabweisknownas doro, chibuku, hwahwa, mhamba or uthwala in

different regions of the country(Chamunorwa etal., 2002).The traditional doro brewingprocess (Figure 4) has beendescribed by Benhura et al.(1989). The brewing processstarts with the malting of redsorghum toproduce a substancecalled masvusvu. Sorghumgrains are soaked in waterfor 24h at room temperature.They are then placed in a sack,washedandlefttogerminatefor2-3days at room temperature.After this stage, the seedlingsare sun-dried for 3days and thesemi-drymalt grains aregroundor crushed. Approximately 24lof water is mixed with 7kg ofsorghummaltflour.Thismixtureis heated while stirring untilboiling.Themasvusvuiscooled,diluted in clay pots and left tosour at ambient temperature forabout 2days. On the third day,the soured product (mhanga) isboiled for 3-5h, reducing theoriginal volume by a quarter inthe process.The boiledmhangais allowed to stand overnightafterwhichtime,moremaltflouris added. Typically, the amountof malt added is about half theamount used at the beginningof the brewing process. On thesixth day, some masvusvu, two

to three timesmore than the amount cooked on thefirstday,ispreparedandallowedtocool.Meanwhile,a small portion of themhanga is strained and keptseparately. The strainings (masese), the rest of theunstrained mhanga and the fresh portion of cooledmasvusvu are allmixed togetherwithwater to yieldbiti.Themixture is left to ferment forabout2handtheresultingproduct,calledmadirwa,isthenstrained,mixedwith the previously strainedmhanga and lefttofermentovernight.Thefermentationprocesstakes5-7daysdependingonambient temperature.Ethanolisthoughttobethemainalcoholcontainedinthefinaldorobeer(about4%v/v).

5.4. Dolo of Burkina Faso

Dolo is a popular traditional alcoholic beveragemanufacturedinBurkinaFaso,andismostoftenmadefromredsorghummalt(Hilhorst,1986).Thetraditionalmaltingprocessfordolo (Figure 5) issimilar to that

Figure 3. Traditional manufacturing processes of Merissa beer — Processus traditionnel de fabrication de la bière Merissa(Dirar,1978).

Sorghum grains

MaltedFine flour

Coarse flour

Malt

flour (5 %)

Half-cookedSlightly cooked

Futtara

Water

Merissa beer

Lactic fermentation (Ajeen, 36 h)

Over cooked (Soorij)

Malt flour (5 %)

Merissa

Water

Alcoholic fermentation

(Deboda, 4-5 h)

Alcoholic Merissa fermentation proper (8-10 h)


Figure 4.Traditionalmanufacturingprocessesofdorobeer—Processus traditionnel de la fabrication de la bière doro.

Sorghum grains Water (24 h)

Water

Steeping (24 h)

Germination (2-3 days)

Drying (under sun, 3 days)

Mix malt flour (7 kg) with water (24 l)

Cooling (Masvusvu)

Cooking (3-5 h)

Malt

flour

Masese

Doro beer

Alcoholic fermentation (5-7 days)

Mix Madirwa with Masese

Fermentation (2 h, Madirwa)

Mix Mhanga, Masvusvu

with water (biti)

Lactic fermentation (48 h, Mhanga)

Milling

Boiling


described for the ikigage beer. The maltobtainedisusedbythetraditionalbrewers(“dolotières”) to prepare the dolo beer.Sorghum malt flour is mixed with water(1:10,w/v)andthemixtureisthendecanted(for approximately 10-12h) to separateoff the enzymatic supernatant phase withprecipitatecontainingstarch.Waterisaddedtotheprecipitateandthemixtureisboiledtogelatinizestarch,butthesupernatantisnotboiled(Dickoetal.,2006).Aftercooling,theprecipitateisfilteredtoseparatethesolublecomponents (starch, sugars, proteins, etc.)andtheresidue(usedasanimalfeed).Thefiltrate ismixedwithprevious supernatantandboiledat65-70ºCfor12-16hinorderto obtain the wort. This method seemsto be a good traditional mashing processfor producing sorghum wort with a highfermentable rate for sugars, because theprocessovercomestheproblemofsorghumstarchgelatinizationandhydrolyticenzymedenaturation.After this stage, the wort iscookedandthencooledovernighttoroomtemperature (30-40ºC). The cooled wortis inoculated with a traditional leaven tostart the fermentation process, leading tothedolo beer after12-24h (Griffonet al.,20011, cited byMaoura et al., 2009). Thefinaldolobeerisopaque,witharedcolor,analcoholcontentof2-4%v/vandapHof4-5(Dickoetal.,2006).

5.5. Pito and burukutu of Nigeria

Pito andburukutu are traditionalNigerianalcoholic beverages brewed with red orwhite sorghum malt and/or maize. Thebrewing process for pito (Figure 6) hasbeen described by Ekundayo (1969).Briefly, sorghum grains are steeped inwater (24-48h) and then, drained. Thegrains are then allowed to germinate forfour to five days and are sun-dried beforegrinding.Themaltflourismixedwithwaterand themixture is thenboiledfor3-4h toformaslurry.Duringthemashingstageofburukutu production, adjuncts are addedin the form ofgari (a farinaceous starchypowder produced from cassava, Manihot esculenta). However, adjuncts are not

1GriffonD.&HébertJ.P.,2001.Bière et dolo : document de cours.Montpellier,France:Ensia-Siarc.

Figure 5. Traditionalmanufacturingprocessesofdolobeer—Processus traditionnel de la fabrication de la bière dolo.

Sorghum

grains

Water

Spent

Filtrate

Dolo beer

Starter

(previous Dolo)

Filtration

Cooking (100 °C)

Supernatant

Mashing (65-70 °C)

Cooling wort (30-40 °C)

Cooking (100 °C)

Fermentation (12-24 h)

Sediment

WaterSteeping (24 h)

Germination (48 days)

Drying (under sun)

Mix malt flour with water

Grinding

Decantation (10 -12 h)

Juice from Hibiscus esculenta


addedduring the production ofpito (Faparusi et al.,1973; Ekundayo, 1969). After cooling, the paste isfiltered and left in spontaneous lactic fermentation(acidification)atroomtemperatureforapproximately12h. More water is added and the mixture is thencooked for 3h and cooled to around 20 to 29°C.Cooledwort is subsequently left to ferment at roomtemperature for 12-24h. The two resulting productsare:atopclearsupernatant,called“pito”andathickbrownsuspension,called“burukutu”.

5.6. Amgba or bili bili of Cameroon

Amgba,wellknownbythenamebili bili,isaverypopular traditionalalcoholicbeverage in Cameroon (among theBaya ethnic group). The drink isbrewedprimarilyusingsorghummalt(mouskouari or djigari variety), butmillet malt (fonio variety) can alsobe associated with mouskouari. Thetraditionalbrewingprocess(Figure 7)for this beer has been described byChevassus-Agnes et al. (1979). Thesorghum grains are soaked in waterfor12 to72hat roomtemperature inorder toobtainamoisture levelof35to 40%.The grains are then left in aheap in a container or spread out ona germination device (green plantainleaves, beaten soil, rocks) to form alayer (3 to5cmin thickness)andarekept covered until rootlets appear.If needed, initial moisture levels aremaintained by spraying with water.The germination time is on average4days.After this step, the grains aredried under the sun for a maximum1day and ground into a fine flour.This malt flour is then mixed withwater and sap (gombo) from trees. Inparticular gombo from Triumfetta sp.seemstoimprovetheflocculationandfiltrationoftheinsolublematterduringdecantation. This operation using thesap resembles that carried out duringthe clarification of barley beers inEuropean breweries. However, thesorghum beer clarification processusing gombo after fermentation hasnot been extensively investigated.After 1 to 2h of decantation, theenzymatic supernatant phase iscarefully collected, while the settledresidueiscookeduntilboilinginordertogelatinizethestarch.Aftercooking,thethickmashobtainedismixedwith

the previous supernatant at 65-70°C. The mixtureis thenfilteredbydecantationorusinga traditionaldevice similar to the filter-tank used in industrialWestern brewing.Very often, the traditional brewerleavesthefiltrateinspontaneouslacticfermentationtoacidifythewort.Afterboiling,thewortiscooledto approximately 30°C and then inoculated withtraditional leaven, “affouk” to start fermentation.After12to24hoffermentation,theresultingamgbacanbeconsumed.

Figure 6. Traditional manufacturing processes of pito beer—Processus traditionnel de fabrication de la bièrepito(Asiedu,1991;Achi,2005).

Sorghum and/or

maize grains

WaterSteeping (48 h)


Drying (under sun)


Grinding

Boiling (3-4 h)

Boiling

Filtration

Cooling

Cooling

Spent

Natural inoculum

Adjuncts (gari) are addedt to Burukutu

production

Fermentation (acidification 10-12 h)


Pito or Burukutu beer

Starter (sediment

from previous brew)


5.7. Tchoukoutou of Benin and Togo

Tchoukoutou, or chakpalo is atraditional alcoholic beverageproduced in Benin and Togoprincipally using sorghum malt (redandbrownvarieties),butotherstarchsources, such as millet or maize canbe used as adjuncts or as substitutes(Kayodé et al., 2005; Osseyi et al.,2011). Tchoukoutou and chakpaloare distinguishable by both theirappearance and taste. Tchoukoutouis an opaque (turbid) and acidic beerwhile chakpalo is a clear and sweetfluid beer. The traditional brewingprocess (Figure 8) for tchoukoutouhas been described by Kayodé et al.(2005, 2007b). Approximately 27kgofgrainsaresoakedinwaterfor9 to12handthenlefttogerminateduring72 to 85h.After this step, the grainsare dried under the sun (7-15h) andgroundintoafineflour.Thismaltflouris then mixed with water and left indecantation.Afterdecantation(1-2h),the enzymatic supernatant phase iscollected and the residue containingstarchisgelatinizedbygradualheatinguntil boiling for 2h. The thickmashobtained is mixed with the previoussupernatantphaseandleftinastateofacidifying (lactic) fermentation (13-14h).After this stage, themixture isfilteredtoobtainthewort.Aftercooking(6-9h),cooledwortisinoculatedwitha traditional leaven (known as kpètè-kpètèintheBariba,DentiandYorubalanguages) in order to start alcoholicfermentation. After 13 to 14h offermentation,tchoukoutouisreadyforconsumption.ThisbeerissourwithapHof3.2:itcontainsarelativelyhighbutvariable levelof solidsandcrudeprotein(Kayodéetal.,2007b)andhasa 4% (v/v) alcohol content (Osseyietal.,2011).

2VanLiereM.J.,1993.Coping with household food insecurity: a longitudinal and seasonal study among the Otammari in North-Western Benin.Wageningen,TheNetherlands:WageningenUniversity.

Figure 7.Traditionalmanufacturingprocessesofambgabeer—Processus traditionnel de la fabrication de la bièreambga(Chevassusetal.,1979).

Sorghum

grains

Water, 12-72 hSteeping (12-72 h)

Germination (4 days)

Drying (under sun, 24 h)


Decantation (1-2 h)

Supernatant

Filtration


Traditional

leaven “Affouk”

Filtration

Ambga beer

Spent

Spent

Cooking (100 °C)

Cooking (100 °C)

Cooling (30 °C)

Mashing (65-70 °C)

Sediment

Sap from “Gombo”

(Triumfetta sp.)

Grinding


6. SOCIO-CULTURAL ASPECTS AND NUTRITIONAL STATUS OF SORGHUM BEER

African cereal beers (made from sorghum, millet,maize, etc.) have ancient origins. They may haveoriginatedinEgyptorMesopotamia,wherebeerswere

being produced by at least 3,500BC,andprobablymuchearlier(Briggsetal.,1981). The first mentions of sorghumbeerormilletbeercomefromtheArabtravellerswho,inthe6thand7thcenturies,praisedthemeritsofbeermanufacturedin the Sahel region, in particular themerissabeerofSudan(HuetzdeLemps,2001). The manufacturing of sorghumbeers is a tradition preserved byAfrican women brewers and passeddown to thenextgeneration. InAfricantradition, sorghum beer symbolizes thewoman, representing silenceanda tacitacceptance of the “entente” betweenthe peoples. In ancient times, royaltiesdue to the local authorities were paidonlyintheformofsorghumorsorghumbeer. Sorghum beer is called the “milkof the hoe” inAfrica (amata y’isuka inthe Rwandese language), affording thebeer noble qualities (De Lame, 1995).Sorghum beer is an ancestral beveragewidely used in various festivals andAfrican ceremonies such as marriage,praying for rain, communication withancestors, births, the handing-over of adowry,circumcision,burialceremonies,andthepopularannualsorghumfestival(Kayodéetal.,2007b;Lyumugabeetal.,2010). In Rwanda or Burundi, dowryhanding-over ceremonies start initiallywith the consumption of traditionalsorghumbeer.Therepresentativesofthetwo families greet each other around aclay jug (called an ikibindi) filled withsorghum beer because ikigage beersymbolizes the complementarity of thesexes (De Lame, 1996). Traditionalsorghum beer is also consumed aftercommunityworkormeetingsofmutualassociations, inorder toprovide energy(VanLiere,19932,citedbyKayodéetal.,2007b).

Traditional sorghum beer is mainlyconsumed by the poorest in society,and contributes significantly to the dietof millions of African people (Kayodéetal.,2007b).It isveryrichincalories.It is also rich in the B-group vitamins

includingthiamine,folicacid,riboflavin,andnicotinicacidandishighinessentialaminoacidssuchaslysin(Table 2).

According to Chevassus-Agnes et al. (1979), thesignificant dry matter losses during sorghum beerpreparationseemtobebalancedbytheimprovement

Figure 8. Traditional manufacturing processes of tchoukoutoubeer—Processus traditionnel de fabrication de la bière tchoukoutou.

Sorghum

grains

Water (9-12 h)Steeping (9-12 h)


Drying (under sun, 7-15 h)


Decantation (1-2 h)

Supernatant

Filtration


Tchoukoutou beer

Traditional

leaven

“Kpètè-kpètè”

Spent

Boiling (6-9 h)

Boiling (2 h)

Mashing (65-70 °C)

Fermentation (acidification 13-14 h)

Cooling (30 °C)

Sediment

Grinding


in protein and amino-acid digestibility, mineralavailabilityandvitamincontent.Germinationincreasesthedigestiveavailabilityofessentialaminoacids,whichispreservedinsubsequentstagesofproduction(Taylor,1983).Fesolubilitygraduallyincreasesduringthebeermakingprocess(germinationandfermentation)andishighly correlated with phytate and reactive phenoliccompoundsintheproduct.However,importantlossesof minerals occur during the beer making process,particularlyduringthemashingstage;thus,thequantityofFeavailable toconsumers is restricted(Kayodéetal., 2007a). Phenolic groups and tannins present insorghumgrainimpair thegrain’snutritionalvaluebysequesteringexogenousandendogenousproteinsintheformofindigestiblecomplexes(Maouraetal.,2009).Ontheotherhandthebeerbrewingprocessremovessignificant amounts of tannin (Dhanker et al., 1987;Osuntogunetal.,1989).Nevertheless, thenutritionalvalueofsorghumbeersisgenerallyhigherthanthatofEuropeanbarleybeers(Table 3)duetothepresenceofyeast,lacticacidbacteriaandothersuspendedmaterial.Duetotheirlowalcoholcontentandthelargequantity

of suspended solids,many consumers consider theseindigenousfermentedsorghumbeers tobemoreofafoodthanabeverage.

7. SHELF LIFE OF TRADITIONAL SORGHUM BEER

Traditionally-made sorghum beers have a poorkeeping quality. The limited shelf life (stability)of sorghum beers has been reported as the majorproblem confronting commercial brewers in Sudan(Dirar,1978),inTanzania(Tisekwa,1989),inNigeria(Sannietal.,1999)andinRwanda(Lyumugabeetal.,2010).

Sorghum beer is consumed while it is stillfermenting.Thewortfromwhichthebeerismadeisnotheated–orotherwisetreatedpriortotheadditionofyeast,andthedrinkthereforealwayscarriesaresidualmicrofloraoriginatingmainlyfromitsingredients.Theresulting beer is thusmicrobiologically unstable i.e.,infected at varying levels with yeasts and bacteria.Sanni et al. (1999) isolated the following bacteriafromdeterioratingsorghumbeer(pitoandburukutu):

Table 2.Comparisonofchemicalcompositionsofsorghumgrain, malted sorghum and Cameroonian sorghum beer“amgba”(expressedfor100gdrymatter)—Comparaison de la composition chimique de grain de sorgho, malt de sorgho et bière de sorgho du Cameroun « amgba » (exprimé à 100 g de matière sèche).

Grain Malt AmgbaCalories(kj) 381 380 394Protein(g) 9,4 9,8 8,7Lysine(g%proteins) 3,3 3,7 7,2Lipids(g) 2,8 2,2 0,3Totalsugars(g) 85,6 86,2 86,1Non-digestiblesugars(g) 2,3 3,7 0,3Ash(g) 2,1 1,7 4,1Calcium(mg) 11 9,3 20,7Totalphosphorus(mg) 319 327 630Phyticphosphorus(mg) 166 85 112Potassium(mg) 391 361 1101Sodium(mg) 14,5 14,7 26,9Thiamine(µg) 407a 426b 3441c

Riboflavine(µg) 98 231d 760Niacin(mg) 4,3 5,3 8Source:adaptationofMaouraetal.(2009)fromChevassus-Agnesetal.(1979)—adaptation de Maoura et al. (2009) à partir de Chevassus-Agnes et al. (1979);Extremevalues—valeurs extrêmes:a:170-545;b:168-565;c:1693-5241;d:169-300.

Table 3. Nutrients in African and European beers(per portion of 100 g) — Éléments nutritifs des bières européennes et africaines (par portion de 100 g).

African traditional sorghum beers

European lagerbeers

Calories(kj) 155 164Drymatter(g) 7,9 4,0Insolubledrymatter(g) 3,9 0Protein(Nx5,7) 0,6 0,3Carbohydrate(g) 4,8 3,2Alcohol(g) 2,9 4,0Ca(mg) 2,2 6,3P(mg) 39 40K(mg) 84 47Na(mg) 1,1 3Fe(mg) 2,55 0,1VitaminB1(mg) 0,11 0,003VitaminB2(mg) 0,05 0,04Niacin(mg) 0,43 0,71VitaminB12(µg) 0,03 -Pantothenicacid(mg) 0,09 0,18VitaminC 0,04 _Source:Nout(1987).


Aspergillus aceti, Aspergillus hansenii, Aspergillus pasteurianus,Lactobacillus plantarum,Lactobacillus fermentum, Lactobacillus brevis, Alcaligenes,Saccharomyces cerevisiae, Micrococcus spp.,Candidaspp.,Bacillus licheniformis,Flavobacteriumspp., Candida mycoderma, Hansenula anomala,Saccharomyces diastaticus (questionable), Bacillusspp.andRhodotorulaspp.

Sorghum beers spoil rapidly because they areactively fermenting when solid, with organisms inaddition to yeasts flourishing in the rich medium.During fermentation, yeasts initially increase innumber.Theninthelaterstageoflogarithmicgrowththe production of ethanol starts and proceeds duringthestationaryphase.Ithasbeenobservedthatduringthis time, very little or no increase in thenumberofcontaminating organisms seems to occur. However,attheendoffermentation,theyeastsdie,orelsetheyundergoautolysisandtheircellconstituentsarereleasedintothebeer.Withlittleornocompetitionfromyeastsfor the readily available nutrients, contaminatingmicroorganisms increase rapidly innumberand theirmetaboliteschangetheflavorofthebeer.Becauseoftherelativelyhightemperatureoffermentation,thesesequential events occur within a short time period.Thisperioddoesnotusuallyexceedmorethan3daysin summer or 5days in winter before this spoilageoccurs. Themetabolic activities ofmesophilic lacticacidbacteriaareprimarilyresponsibleforthespoilage.Thesebacteria, alongwithotherundesirablebacteria(Acetobacter),produceaceticacid,volatileoff-flavors,fruityodors,andpellicleswhichrenderthetaste,odorand texture of the beer unacceptable to consumers

(VanderWalt, 1956).Table 4 describes the typesofspoilageduringtheconservationofsorghumbeers.

The flash-pasteurization method increases theshelf life of industrial European beers by destroyingspoilagemicrobes.Unfortunately, this process is notapplied in traditional sorghum beer-making. Earlyattempts at pasteurization failed because they led toan unacceptable increase in beer viscosity–throughfurther gelatinization of starch and elimination ofamylolytic enzymes–and also eliminated the beer’scharacteristic effervescence by killing the activeyeasts (Novellie etal., 1986). On the other hand,pasteurizationofbeer results in thekillingofa largeproportionofyeastcells,therebymakingtheB-groupvitamins they contain available to human consumersof beer (VanHeerden, 1987). Post-fermentationpasteurizationhasenabledtheshelflifeof“tugelagold”sorghumbeertobeextendedtoanextentcomparableto that of European barley beers (Haggblade et al.,2004). Recently, Osseyi et al. (2011) were able toobtain stability in the tchoukoutou beer for at least6months after 3h of bottle fermentation stopped bypasteurizationinawaterbathat75-80ºCfor15min.

8. USE OF STARTER CULTURES TO IMPROVE SORGHUM BEER

A starter culture may be defined as a preparationor material containing large numbers of variablemicroorganismsselectedfortheirpropertiesandtheirharmlessness, which may be added to accelerate afermentationprocess(Holzapfel,2002).

Table 4.Spoilageoftraditionalsorghumbeers—Détérioration des bières traditionnelles à base de sorgho.Microorganisms Chemical produced Odors Other effectsAcetobacter sp. Aceticacid Vinegar PelliclePediococcus sp. Lacticacid RopinessLactobacillus sp.(homoferm) Lacticacid RopinessLactobacillus sp.(heteroferm) Lacticacidandaceticacid Ropiness,turbidityLeuconostoc sp. Diacetyl

2,3-butanediolButter/honeySweet

Zymomonas sp. Ethanol,CO2,acetaldehydeH2S

RottenapplesRotteneggs

Obesumbacterium sp. Dimethylsulfide Parsnip,cookedcabbagemoldyCandida sp. Fruity PelliclePichia sp. PellicleRhodotorula sp. RedcolorationHansenula sp. PellicleSaccharomyces sp.(wildstrains) Diacetyl Phenolic,butter/honey SuperatenuationSource:Haggbladeetal.(2004).


InAfrica,startersareusedintheformoftraditionalleaven,resultingfromspontaneousfermentationofthewort.Asaresult,boththedesirableandnon-desirablestrains contained in the leaven are reintroducedwithfermentation,inducingthefermentationofthesorghumwort. For example, the fermentation of the ikigagebeerisinitiatedbyatraditionalleaven(umusemburo),which contains Saccharomyces cerevisae, Candida inconspicua,Issatchenkia orientalis,Candida magnoliaand Candida humilis, Lactobacillus fermentum, Lactobacillusbuchneri,Aspergillussp.,StaphyloccocusaureusandEscherichia coli(Lyumugabeetal.,2010).Selecteduseofadominantspecies(e.g. S. cerevisiae,Lactobacillus sp. or I. orientalis) could stabilize theorganoleptic quality of this beer, increase its ethanolcontentandimproveitshygienicquality.

The use of starter cultures has been appliedsuccessfullytomanyproducts,andstudieshavebeenundertaken in thedevelopmentof starter cultures formany other fermented foods from Africa (kivunde,ogiandtogwa)(Teniolaetal.,2001;Kirmaryoetal.,2002;Mugulaetal.,2003).Researchonimprovementinthequalityoftraditionalsorghumbeerhasfocusedon the adaptation of the starter culture. Sefa-Dedehet al. (1999) used a pure culture of S. cerevisiaeand a mixture culture comprised of S. cerevisiaewith Kloeckera apiculata or Candida tropicalis, toproduce in the laboratory a pito beer containing ahigh ethanol content compared to traditional pito.By contrast, they also found that a mixture of threecultures (S. cerevisiae,K. apiculataandC. tropicalis)asthestarterproducedapitobeerwithalowethanolcontentcomparedtothetraditionalpitobeer.Orjiet al.(2003) found that S. cerevisiae in combination withLactobacillus plantarum,asastarterculture,alsoledtothesatisfactoryproductionofapitobeerwithatasteand aroma similar to localpito beer, butwith a lowethanolcontent.N’Guessanetal.(2010)successfullyused S. cerevisiae in combination with C. tropicalisas starter cultures for the alcoholic fermentationof the tchapalo beer, but further investigations arerequired before a definitive conclusion.Glover et al.(2009) showed that dolo beer produced from startercombinations of one strain of L. fermentum andboth S. cerevisiae strains had a taste and aroma thatdid not differ significantly from the local dolo beer.This kind of research needs to be widened to othertypes of sorghum beer because the microorganismsinvolvedinspontaneousfermentationareverydiverse.

When the starter is adapted to the substrate, itsuseimprovescontrolofthefermentationprocessandthe predictability of its products (Holzapfel, 1997).Inaddition,itfacilitatescontrolovertheinitialphaseof fermentation (Holzapfel, 2002). In the sameway,the hygienic quality and acceptability of Africantraditionalfoodscouldbeimprovedwiththeuseofa

suitablestarter (Granetal.,2003).Theuseofstartercultures also reduces the organoleptic variations andthe microbiological instability of African fermentedfoods(Kirmaryoetal.,2002).

However, the use of starter cultures does notprovide an absolute guarantee against failure offermentationprocess,nordoesiteliminatethehealthhazards associated with pathogens, toxinogens, ortoxic components or residues (Holzapfel, 2002).The metabolic activities of desirable fermentationmicroorganisms must be supported by observingthe basic principles ofGoodManufacturing Practice(GMP).

9. CONCLUSION

Traditional sorghum beers have a socio-cultural andnutritionalvalueinAfrica.ComparedtothebrewingofEuropeanbeerwithbarley, thebrewingoftraditionalsorghumbeerischaracterizedbythecomplexityofthemaltingprocess,thespeedandshorttimeofalcoholicfermentation,andtheexistenceoflacticfermentation.

InAfrica, the association of sorghum with othercereals(e.g.Eleusine coracana,Pennisetum glaucum,sweet potato) available in Africa could solve theproblemofthelackofβ-amylaseinsorghummaltandprovideameansofavoidingtheuseofthecommercialenzymesandbarleymalt.

The pasteurization of sorghum beer appearsmost promising for resolving the brewer’s perennialprincipalproblemofashortershelf life.However, inorder for this to happen, research will be needed toensurethenecessaryrefinementsinpasteurization,andfactorybrewerswouldneedtoadoptthepasteurizationprocessastheirproductionstandard(Haggbladeetal.,2004).

The presence of unspecified microorganismsfromtraditionalleavencomplicatesthecontrolofthefermentation process and yields products of variablequality.Theuseofstarterculturesseemstobeagoodmethodtoreduceorganolepticvariationsandtoreducetheriskofcontaminationwithpathogenicorganisms.This approach would also increase the chances ofpreserving of traditional sorghum beer, giving ita longer shelf life. The existing variations in theproduction processes ofAfrican traditional sorghumbeercouldbeincorporatedintothedevelopmentofalargevarietyofsorghumbeersinAfrica.

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