From Starter to Finish: Producing Sourdough Breads to Illustrate The

U ~~~~~~~~~ I- c Downloaded from http://online.ucpress.edu/abt/article-pdf/67/2/96/52227/4451793.pdf by guest on 26 September 2021 FROMSTARTER TO FINISH: ProducingSourdough Breads To Illustrate I- the Use of Industrial Microorganisms STEPHENC. WAGNER E he use of beneficialmicroorganisms for the LS strain.This cultureis subsequentlyused to pro- productionof pharmaceuticals,food, food additives, duce various starter cultures (sizeable cultures of beverages,and chemicalsis a very importantaspect the LS strainto be used in the fermentationprocess) of microbiology.Despite its importance,students in for continuous propagation of the bacterium. the typicalmicrobiology laboratory course arerarely Studentsuse the startercultures to make their own exposed to these organisms beyond growing and sourdoughbread and compareand contrastthem in observingthem in pure culture.In orderto familiar- terms of odor, texture,color, and appearance.These ize our students with a typicalindustrial microbiol- approaches, with appropriatemodifications, have ogy process from startingwith a microorganismto also been found to be suitable for biology lab cours- ending with a useful product,a simple,cost effective es for students not majoringin biology or microbi- laboratory exercise was developed that utilized ology. A number of these modifications are also Lactobacillussanfranciscensis (LS), the bacterium described. used to make San Franciscosourdough bread. This article describes an approach where stu- Background Information dents first develop and make a medium to grow an For centuries, ancient Egyptians,Romans, and Greeksused grains,such as barleyand oats, to make ratherunappetizing porridge or flat cakes. At some STEPHEN C. WAGNER is Associate Professorin the Department of Biologyat Stephen F. Austin State University,Nacogdoches, point the Egyptiansmade two significantadvances TX 75962; e-mail: [email protected]. that allowed them to produce something much 96 THEAMERICAN BIOLOGY TEACHER, VOLUME 67, NO.2, FEBRUARY2005 more enjoyableto eat. First, they started cultivating Table1. wheat (Triticum sp.) along Comparisonof"wild" yeasts with standard breadmaking yeast (Saccharomyces cerevisiae). with other grains, such as barley. Secondly, the Criteria "Wild"Yeasts Saccharomycescerevisiae Egyptiansdiscovered, prob- SpeciesNumber Several One ablyby accident,that wheat dough did somethingnever OptimalpH Acidic(pH 2.5 - 5.5) Neutral/alkaline(pH 6.0 - 8.0) seen before after being set BreadTextures Determinedby yeasts in mixture Uniformtexture aside; it began to ferment and leaven. Because the RisingTime > 10 hr. < 2hr. wheat contained gluten, the protein in wheat that gives the dough its cohe- siveness and elasticity,some of the gases produced by tion. The yeasts were trappedfrom the environmentby leavening were trapped within the dough. When the simply exposing a mixture of wheat flour and water or Egyptiansbaked this newfounddough, the productwas milk to the air. The resulting mixture of yeast species Downloaded from http://online.ucpress.edu/abt/article-pdf/67/2/96/52227/4451793.pdf by guest on 26 September 2021 completely different from anything they had experi- depended upon the type of flour used and the environ- enced. It was the first recognizableloaf of sourdough mental conditions that prevailedduring the fermenta- bread, puffy and crumbly inside with a dark, fragrant tion process. In contrast,today's mass-producedbread crust (Jacob,1944; Wood, 1996). is carriedout by the fermentationand leaveningaction of a single yeast, Saccharonycescerevisiae. A sourdough The Egyptianssoon became experts at bakingsour- starterculture begun with S. cerevisiaewill differin sev- dough bread, developing 50 differentvarieties. Bread eral ways comparedwith the starterbegun with yeasts became the major food as well as the currencyof the trapped from the environment,namely in the number day with wages paid in loaves of bread for centuries.In of yeast species found in the starterand the pH at which fact, a painting of the royalbakery of King Ramseswas these culturescan grow (Table 1; Wood, 1996). found in an Egyptiantomb UJacob,1944). The Egyptian art of bread making found its way LactobacillusCultures for Sourdough fromone generationto anotherand fromone cultureto another,eventually finding a place in Americanhistory. The other chief component of sourdoughis the bac- On January24, 1848, more than 4,000 years since the terium Lactobacillus.This bacterium requires maltose pyramidswere built,James Marshalldiscovered gold in (found in flour) to grow and is able to fermentit while Californiaat Sutter'sMill. San Franciscocaught "gold the yeast(s) cannot. The Lactobacillithrive in the acidic fever"so swiftly that within a few months most of the environment caused by the lactic acid that they pro- men had abandoned the town to find their own for- duce. This process,together with the bacteria'sability to tunes (Blumberg,1989); the CaliforniaGold Rush had producean antibioticthat controlsother organismsthat begun. Soon, gold would also be discovered in the might contaminatethe sourdoughstarter, keeps it from YukonTerritory. getting overtakenby other microorganisms.The bacteria also producealdehydes and esters that are unique to Once again sourdoughbread would play an impor- sourdoughbread and may contributeto its flavor(Seitz, tant role in history.Yukon prospectors became known Chung & Rengarajan,1998). as "sourdoughs"because they carriedhomemade yeast starter made of soured milk and flour (Morrell, Specific Organisms Found in San 1941).Thesourdoughs always carried a small amountof starterthat had been passed on to them from another Francisco Sourdough prospector.After mixing it with waterand flourto make Although San Francisco bakeries continue to use dough, they baked sourdough bread, always saving dough made from starter cultures formulated during some starterfor the next camp. Some West Coast and the Gold Rush, the specific organisms responsible for Alaskan bakeries claim that their sourdough cultures this bread remained a mystery until the early 1970s. originated from some of these starters (Dworkin & The yeast responsible for the leavening action in San Dworkin, 1987). Francisco sourdough was identified as Saccharomyces exiguus(Sugihara, Kline & Miller,1971). This yeast has Yeast Cultures for Sourdough since been reclassified as Candida humilis (Wood, 2001). It is capableof growingin an acidic environment starter culture required the pres- The sourdough and unable to utilize maltose. Consequently the yeast ence of at least one species of yeast to initiatefermenta- PRODUCINGSOURDOUGH BREADS 97 seems to be able to coexist with sourdoughbacteria that require or prefer maltose and produce organic acids Table2. upon its metabolism(Wood, 2001). Lactobacillussanfranciscensismedium (modified from Kline & The lacticacid bacteriumtypically found in the sour- Sugihara,1971). dough is Lactobacillussanfranciscensis. The bacteriaare Constituent Amount gram-positive,nonmotile, catalase-negativerods that number30 to 100 times more than the yeast cells found Maltose 20g in the dough.They produce both lacticand aceticacids as YeastExtract 3 g well as carbondioxide and requirelarge amounts of maltose in order to produce heavy growth.The acids make FreshlyPrepared Yeast Extract 15mL sourdoughbread eight to ten times more acidic (pH 3.8 Tween80 to 4.3) than conventionalbread. The two organismsgrow 3g togetherin a mutualisticrelationship, each metabolizing a Trypticase 1.5g differentcarbohydrate that producesthe conditionsthat protectthe culturefrom contamination by other microor- DeionizedWater 1000mL ganisms. This allows the startercultures used to make Downloaded from http://online.ucpress.edu/abt/article-pdf/67/2/96/52227/4451793.pdf by guest on 26 September 2021 San Franciscosourdough bread for overa centuryto con- pHadjusted to4.0 with HCI tinue to be used (Sugihara,Kline & Miller,1971). (Tween80). Afterstudents preparethis medium, 30 mL Procedures aliquots are placed in 250 mL flasks; the flasks are capped with a foam or cotton plug and autoclavedfor Objectives 20 minutes (121?C, 15 psi). Afterthe media has cooled Studentswork as individualsor teams to: the students should add a small amount of a lypholized cultureof LS (AmericanType Culture Collection [ATCC] * Develop and preparea medium to grow a culture # 27651) and incubate these cultures on a reciprocal of LS. shaker(200 rpm) set at 32 C until the culturebecomes * Develop a starterculture of this organism. turbid(72 hours). * Use the starterculture to make sourdoughbread. Starter Culture Preparation. Each student or team is assigned the recipe for a particularstarter culture in * Compare and contrast their bread with those order to compare the effectivenessof several types of other students. produced by startercultures (Table 3). Alternativelythe students can be requiredto find their own starterculture recipes. The Week 1. Preparation & Inoculation of students preparetheir starterculture and place it in a Lactobacillus Medium & Starter Culture plastic or glass container (Ca 750 mL); the containers Students first preparea medium to grow pure cul- are loosely covered with a lid and incubated at room tures of LS.This medium requiresingredients that have temperature.Each culture is observedand stirredvigor- to be preparedfresh. The students learn how to prepare ously with a plastic spoon once a day until it is used to and properlysterilize the medium so it can be inoculat- make the bread.A successful starteris indicatedby the ed with

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