How-To-Do-It FermentationMicrobiology Ma king Cheese, Yogurt &r Buttermilk as a Lab Exercise MaryAnneDrake John McKillip In the introductory microbiology www.cheesemaking.com;tel: 413-628- 3.5%are protein, 4% are lactose (milk Downloaded from http://online.ucpress.edu/abt/article-pdf/62/1/65/49367/4450828.pdf by guest on 28 September 2021 laboratory, food microbiology exer- 3808 for catalog). Other related sup- sugar), and 0.5% are minerals. cises are frequently placed at the end plies can be obtained from this com- What The primaryprotein of the quarter or semester, if time pany, as well. happened? in milk is casein, which is sensitive to allows after covering medical bacteri- acid. In the presence of acid, caseins ology or mycology. In the instances Objective become less soluble and tend to clump when food microbiologyis given atten- together. Casein is also sensitive to a tion earlierin the term, demonstrations Demonstrate proliferationand pro- particular enzyme called rennet, an are often used or discussed that still duction of acid by LAB during the acid protease. This means that rennet do not allow the students in the lab making of cheese. acts on (cleaves) milk protein (casein) to actually see what pro- the chance and has optimum activity under acidic are taking place in, for example, Procedure cesses conditions. When the enzyme rennet setup. Although a food fermentation A. Take fresh pasteurized milk acts on casein, the latterbecomes even topics could be presented in these (usually 11) and warm to room tem- less soluble. The loss of solubility is in lecture portion of more detail the peratureusing a water bath or double what makes the thick coagulum microbiologyclass, the end the general boiler. Add the entire packet of cheese form in fermented milks. In of these fermenta- (curds) results (products) culture. Stir thoroughly and cover. this exercise the cheese culture that the students tions are never seen by Incubate at room temperatureor in a was added to the milk contained The exercises can firsthand. following 250 C incubator for 18 to 24 hours. cheese LAB and powdered rennet.The in an introductory be done by students When finished, the milk should be bacteria produced lactic acid which all at once or sepa- microbiology lab solid (coagulated);whey (pale yellow lowered the pH and made casein less time allows, and result in rately, as liquid) may be visible around the soluble. Under the acidic conditions and relatively fool- fast, inexpensive edges, and a clean acid aroma should produced by the LAB, the enzyme products that proof food fermentation be present. rennet cleaved the caseins and made themselves-by students can evaluate B. Dump the coagulated milk into them even less soluble, thus forming the is eating! In each case, procedure a colander lined with cheesecloth or the coagulated milk which was then by a discus- presented first, followed coarse uncolored clean fabric and further drained to make cheese. sion of the process and principles allow to drain for 4 to 6 hours. During behind each fermentationreaction. this time it will be necessary to occa- What is whey? Whey is the yellowish sionally take a clean spoon and scrape liquid that is produced during the the sides of the colander to facilitate making of fermented dairy foods. As Exercise I-Cheese whey draining, allowing the coagu- the acid-sensitive caseins become less and water (whey) This lab is performed using freeze- lated milk to become more solid and soluble coagulate, If have ever pur- dried lactic acid bacteria (LAB) cul- cream-cheese-likein appearance. is squeezed out. you cheese, or tures purchased from the New C. Dump the now mostly solid chased sour cream, cottage the the clear England Cheesemaking Supply Com- cheese into a bowl and sprinkle with yogurt from grocerystore, that you sometimes see when pany, PO Box 85, Ashfield, MA 01330; salts and desired herbs (availablefrom liquid New England Cheesemaking Supply you take off the lid is whey. Whey is Co.) just for taste. Pack the cheese into mainly water,but it also containssmall MaryAnneDrake is an AssistantProfes- a cheesemold (a teacup will do) and amounts of lactose, minerals and non- sor in the Department of Food Sci- place in a refrigeratorovernight. The acid-sensitive milk proteins called ence and Technology, Southeast next morning,free the cheese from the "whey proteins." DairyFoods ResearchCenter, Missis- mold (it should be easy to remove). Tremendous amounts of whey are sippiState University,Mississippi State, It is now ready to eat. produced during industrial cheese- MS39762. John McKiIIip,formerly at making. Because whey contains sugar MSU,is currently an AssistantProfessor and protein, it is an excellent growth in the Departmentof BiologicalSci- Discussion medium for bacteria and has a high ences, LouisianaTechnical University, Ruston,LA 71270. What is milk? Milk is 88%water and biochemical oxygen demand (BOD). 12%solids. Of these solids, 4% are fat, Until several years ago, whey was FERMENTATIONMICROBIOLOGY 65 poured into the sewer system and was Nonfat dry milk powder 4% together produce acid and typical expensive for wastewater treatment Table sugar (sucrose) 5% yogurt flavor. Note that these two LAB facilities. Today, processes have been B. Preblend the powdered milk and are thermophilic, which is why the developed to re-processwhey and use sugar-no lumps! fermentation temperature for yogurt the sugar and proteins in it. C. Disperse the powdered ingredients is much higher than the temperature into cold milk using a hand blender used for cheese or buttermilk. Other What are the bacteria used in cheese or regular blender. bacteriaare often added to yogurt for production? Cheese primarily uses D. Heat the mixture in a water bath health reasons, particularlyin the last genera of LAB called lactococci. In to 850 C for 20 minutes. few years. These bacteria are called particular,Lactococcus lactis ssp. lactis probiotic bacteria, and they E. Cool to 400 C in an ice bath. Add aid in and Lactococcuslactis ssp. cremorisare digestion and intestinal health (but the powdered yogurt culture(avail- widely used to make cheddar cheese. play no role in the production of able from New England Cheese- (It should be noted here that the genus yogurt). The two bacteria most com- Lactococcus was created in 1985 to making Supply Company) and monly used for this purpose are Lacto- include the species formerly known stir thoroughly. bacillusacidophilus and Bifidobacterium as Streptococcuslactis. Although many F. Incubateat 400 C for 8 to 16 hours longum. general microbiology laboratoryman- (until a firm coagulum is formed). uals still refer to this organism by Yogurt can be cooled and con- its former name, the proper name is sumed at this point. Fruit topping can be added to spruceup the taste. Exercise Ill-Buffermilk Lactococcuslactis). Lactococci are homo- Downloaded from http://online.ucpress.edu/abt/article-pdf/62/1/65/49367/4450828.pdf by guest on 28 September 2021 fermentative, meaning the primary *Totalvolume can vary, depending on product from fermentation is lactic class size, so the amounts here are Procedure acid, and not a mixture of various expressed as percent figures, not in A. Buttermilkformula: organic acids (heterofermentative). grams or milliliters. A 1-liter batch Milk (any fat content) 98%* Other types of cheese may employ would implement, for example, 910 other LAB to obtain different flavors. Nonfat dry milk powder 2% grams of milk, 4 grams of dry milk NaCl 0.1% Pasteurizationis the process of heat- powder, and 5 grams of sucrose. ing milk so that all pathogenicbacteria B. Preblend the powdered milk-no are killed. Pasteurizedmilk is not ster- lumps! Also add salt here, for What happened? Yogurt is produced flavor. ile; this is why milk spoils after a few by bacterial fermentation. Unlike C. Disperse the powder into cold milk weeks in the refrigerator.However, no cheese production, rennet is not used. hand pathogens remain after pasteurization. The thick consistency of yogurt is due using a blender or regular blender. The heat treatmentsused for pasteur- to the decreased solubility of casein ization are defined by law: 63?C for in the acid produced by the yogurt D. Heat the mixture in a water bath 30 minutes or 720 C for 15 seconds. culture and by additional ingredients. to 850 C for 20 minutes. The latterheat treatmentis often called Starch, pectin and gelatin are often E. Cool to 250 C in an ice bath; add High TemperatureShort Time Pasteur- added to commercial yogurt to give the powdered buttermilk culture ization, or HTST. There are even it a thick consistency. For our yogurt, (from New EnglandCheesemaking higher heat treatments called Ultra powdered milk is added to provide Supply Co.). Stir thoroughly. High Temperature (UHT) treatments this thickerconsistency. Sugar is added F. Incubateat 250 C for 16 to 24 hours (usually 1000 C for 1 to 2 seconds). to flavor the finished yogurt and to (until a firm coagulum is formed). All milk purchased in grocery stores provide additional carbohydrate for The buttermilkcan now be cooled is pasteurized. the LAB. LAB can ferment lactose in a refrigeratorand consumed. Raw milk, however, can contain (milk sugar) and sucrose (table sugar). *As for yogurt, the amounts here are pathogenic bacteria and has been the expressed as percents, since volume cause of foodborne illness outbreaks. Why is the yogurt mixture heated? can vary according to class size; the Pathogenicbacteria that can be in raw Yogurt, unlike cheese, does not use final percentage of each component milk include Escherichiacoli 0157:H7, the enzyme rennet to aid in gel forma- here should stay consistent regardless Listeriamonocytogenes, and Staphylococ- tion. The heat treatment of 850 C for of volume. cus aureus. All of these bacteria are 20 minutes aids in the formation of a completely eliminated by pasteuriza- smooth gel (coagulum) by denaturing What happened? Buttermilk, like tion.