Article pubs.acs.org/jchemeduc
Beer as a Teaching Aid in the Classroom and Laboratory Jasminka N. Korolija,† Jovica V. Plavsic,‡ Dragan Marinkovic,§ and Ljuba M. Mandic*,† †
Faculty of Chemistry, University of Belgrade, Belgrade, Serbia Mihailo Pupin Secondary School, Belgrade, Serbia § Jarrow Industries, Inc., Santa Fe Springs, California 90670, United States ‡
S Supporting Information *
ABSTRACT: Beer was chosen as a teaching tool to maximize students’ class participation and systemize and enhance their knowledge of chemistry. Viewing beer as a complex mixture allowed the students to learn how to directly apply their chemistry knowledge. Before the “Beer Unit” students were instructed to research beer and acquire data on beer composition and properties. They were also asked to propose a hypothesis about possible chemical links between the components of beer and suggest qualitative analytical experiments. During the laboratory and classroom periods, the students performed experiments, analyzed the results, tested their hypotheses, and solved problems. The multilevel approach generated more discussion topics and acquisition of new chemistry knowledge. The students were also encouraged to point out negative consequences caused by uncontrolled consumption of beer. As a result of this unit, the students obtained the correct answers during chemistry classes, and they gained powerful arguments for discussions and were able to make proper health and life choices. KEYWORDS: High School/Introductory Chemistry, Second-Year Undergraduate, Analytical Chemistry, Laboratory Instruction, Organic Chemistry, Analogies/Transfer, Hands-On Learning/Manipulatives, Food Science, Student-Centered Learning
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analyzed the results, tested their hypotheses, and solved problems. The multilevel approach generated more discussion topics and acquisition of new chemistry knowledge. It should be noted, in Serbia, alcohol consumption is not legally regulated (except for drivers). Some high school students have already had personal experience in consuming beer (which is unfortunately the case even in the countries that outlaw alcohol consumptions by minors). However, most students are familiar with beer and know people who drink beer regularly. Therefore, the Beer Unit gives an opportunity to discuss alcohol use and abuse among youth and the grave consequences of alcoholism. In addition, connection between scientific concepts (science) and occurrences and changes in everyday life can be established during the class.
goal of chemistry education is to provide students with essential knowledge to answer questions about problems in daily living situations. The environment offers many materials, substances, occurrences, and changes that can be studied with theories and experiments and utilized as learning tools for chemistry.1−3 Here, beer was chosen as a chemistrylearning tool. This abundant and inexpensive product is made from natural ingredients (Scheme 1; some uses of the Scheme 1 are listed in the Supporting Information). Beer has a complex composition, a unique production (brewing) process, and preservation and packaging requirements, making it a suitable material to study in chemistry classes, both in theory and experimental work.4−7 The “Beer Unit” was taught to 95 upper-level high school students (18−19 years old, during the fourth year of chemistry classes), divided into four classes. The unit was taught after the students had completed general chemistry, organic chemistry, and biochemistry courses and had acquired basic experimental techniques.8 The complexity of beer was used to explain and systematize many chemical concepts (solubility, solution, heterogeneous and homogeneous mixtures, filtration, pH, indicators, chemical reactions for identification of different chemical compounds, chemical equilibrium, chemical interactions, fermenters, etc.). Students were instructed to research beer and acquire data on beer composition and properties. They were also asked to propose a hypothesis about possible chemical links between the components of beer and suggest qualitative analytical experiments. During the laboratory and classroom periods, the students performed experiments, © 2012 American Chemical Society and Division of Chemical Education, Inc.
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UNIT OVERVIEW The beer chemistry unit started with a student survey (see the Supporting Information) that provided insight into students’ attitudes and habits about beer. The survey indicated how knowledgeable students were about beer and their level of interest in expanding their knowledge. After the students completed the survey, the teacher gave a short introduction and some interesting facts about beer (see the Supporting Information). The survey and introduction took 45 min. To fully engage students and make the class as interactive as possible, the teacher started a discussion with a series of specific Published: February 9, 2012 605
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Scheme 1. Schematic Showing Raw Materials to Beer: Raw Materials, Ingredients, and Products (Squares); Processes (Ellipses); and Properties (Diamonds)
The discussions that resulted from each question listed in Figure 1 are described below. For each question, facts, generated by the students and teachers, are supplied that are essential for the creation of a hypothesis. The experiments suggested and performed are listed. And finally, the topics used for further discussions are briefly outlined.
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IS THE POPULARITY AND LONGEVITY OF BEER DUE TO ITS REFRESHING EFFECT OR ITS UNIQUE TASTE?
Facts
Beer is a complex heterogeneous mixture (gas bubbles are easily visible) with over 8,000 ingredients. In addition to water, it contains alcohols, carbon dioxide, proteins, carbohydrates, salts, organic acids, vitamins, and so forth. Beer is a clear liquid from light yellow to dark brown color. The pH of beer is between 4 and 4.5. Its characteristic bitter taste is caused by aromatic components of barley. Beer foams.
Figure 1. Questions used to organize the beer unit.
questions derived from an overarching question (Figure 1). For every answer or hypothesis given, students needed to • Find and list beer ingredients that determine the properties (alcoholic beverage, taste, refreshing effect, nutritional value, maintenance and protection of our body) of beer. • Propose and perform experiments to prove existence of the listed ingredients and verify beer properties. • Draw conclusions (verify hypotheses) about connections between the beer ingredients and the beer properties (causes for beer popularity and longevity). The experiments proposed by the students and experiments suggested by the teacher are identified as SS and TS, respectively. During the two lab sessions (90 min each), the accepted experiments were performed by the students (SD) or demonstrated by the teacher (TD). The discussion of the experimental results was related to the initial questions; that is, the correlation between an ingredient identified and beer property or properties was assessed. The results from the student experiments and teacher demonstrations were used for further discussions enabling acquisition of new chemistry knowledge.
Experiments
Identification of water with anhydrous copper sulfate reaction (SS, SD) Identification of calcium ion with ammonium oxalate reaction (SS, SD) Identification of chlorides with silver nitrate precipitation (folllowed by dissolution of the precipitate with ammonia and re-precipitation with nitric acid) (SS, SD) Identification of sulfate ions with barium chloride reaction (SS, SD) Determination of beer pH using universal indicator paper (SS, SD) What causes beer acidity? −Evidence of oxyacids shown in reaction with resorcinol in presence of sulfuric acid (TS, TD) What (gas) causes beer bubbles and foam? −Identification of carbon dioxide with calcium hydroxide solution (SS, SD) 606
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Topics for Further Discussion
Testing the composition and properties of the beer foam (beer head) with ninhydrin in alkaline solution (The same test can be performed with Coca Cola foam to compare the two.) (TS, TD)
Ef fect of ethanol on foaming properties. Ethanol lowers surface tension (promotion of the bubble formation) and competes with other surface-active molecules (proteins) for the places in the bubble wall (disruption of the protein networks leads to burst of bubbles). Excessive consumption of beer and its consequences. Regular beer drinkers have the hardest time avoiding alcoholism (empirical data obtained from The Institute for Addictive Diseases) because they ingest larger volumes of alcohol due to ease of drinking large volumes of beer. This causes higher physiological and physical dependence. Unwanted effects are also due to the possible presence of trace quantities of some ergot alkaloids caused by the fungus Claviceps purpurea that can infect cereal grains, including barley.16 Why is alcohol harmf ul to one’s health? Discussion about absorption and elimination of alcohol and its biotransformation in the presence of enzymes (formation of reactive acetyl aldehyde, modifications of biomolecules it reacts with and consequences of such modifications) was initiated. Also, pathological states caused by consumption of alcohol (liver cirrhosis, neurotoxicity, memory loss, expansion of blood vessels or vasodilation, increase in amount of stomach acid, increased diuresis causing imbalance of electrolytes in urine and blood, etc.) were debated.
Topics for Further Discussion
Why is the quality of water used very important for the beer quality? The water must have the correct balance and concentration of ions.9 Identification of anions and cations in beer indicates effect of the water used in beer production. A discussion about the hardness of water and procedures to make soft water (from the hard one) was conducted. Economic justification for a certain water softening process can be discussed too. What causes beer acidity? The students answered that the presence of carbon dioxide and its reaction with water is the cause of beer acidity; most cans or bottles of beer contain 2.2− 2.8 mL of CO2 dissolved in 1 mL of beer.4 A discussion about the equilibrium of the aqueous carbon dioxide reaction, the carbonic acid dissociation, and the two constants ensued, as well as the possible presence of both the molecular and ionized forms of carbonic acid at pH 4. Why beer foams? Why is beer foam denser and more stable than Coca Cola foam? The origin of pressurized carbon dioxide (was it a byproduct of fermentation or result of an artificial carbonization?) was discussed and its liberation or escape upon opening a bottle or can. It was pointed out, because the students did not give an appropriate explanation, that carbon dioxide molecules (bubbles) on their way to the surface of the liquid (beer) became attached to the nonpolar (hydrophobic) parts of protein molecules enabling them to stay with the (beer) system longer. Hence, presence of proteins in beer foam makes it more stable and denser to the point it can be “cut”. Why people drink cold beer? Why is beer chilled before consumption? Is it a question of habit, taste, or chemistry? Chilling beer makes it more refreshing,10 though below 15.5 °C the chilling starts to reduce taste awareness11 and reduces it significantly below 10 °C.12 Beers served unchilled, either cool or at room temperature, reveal more of their flavors.13
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IS THE POPULARITY AND LONGEVITY OF BEER DUE TO ITS NUTRITIONAL VALUE?
Facts
Carbohydrates account for 75−80% of the beer extract before fermentation and are the main source of the beer’s energy content. Regular commercial beers usually contain around 35 g/L (3.5%) of carbohydrates, that is, 3.5 g of which are fermentable, 3.5 g of higher dextrins, and 28 g of easily digestible carbohydrates. There is no starch in beer. Beer has relatively low protein content (1.5−6 g/L, i.e., 0.15−0.6%) and it cannot be considered as a protein beverage. However, it contains all essential and some nonessential amino acids. Beer proteins are hydrolyzed into amino acids used by our body to synthesize its own proteins or as metabolic fuel or energy source. Proteins are found both in liquid and foam.
IS THE POPULARITY AND LONGEVITY OF BEER DUE TO ITS LOW ALCOHOL CONTENT?
Facts
Experiments
Alcohol content in beer ranges from less than 3% alcohol by volume (abv) to around 14% abv. However, that percentage can be increased to around 20% by re-pitching with champagne yeast14 and up to 55% abv by the freeze-distilling process.15 Alcohol is a byproduct of yeast metabolism and is toxic to the yeast; typical brewing yeast cannot survive at alcohol concentrations above 12% by volume. The vast majority of beer consumed has abv around 4% making it a mild alcoholic beverage. Adults can consume a glass of beer daily without an adverse health reaction. Human liver can metabolize 8 g of ethanol (from 200 mL or one glass of beer) within 1 h. Alcohol from a standard beer can (330 mL; 360 mL/12 oz) will take close to 2 h and from a bottle (500 mL) almost 3 h to metabolize. Those are the periods of the probable alcohol impairment.
Starch and reducing sugars test with the Fehling’s reagent and Lugol’s (iodine) solution (SS, SD) Test for the presence of proteins with ninhydrin in alkaline solution (SS, SD) Topics for Further Discussion
A discussion about alcoholic fermentation, metabolic pathways in biological systems, and about generation of energy from fuel molecules. Why beer has an expiry date? When and why beer becomes cloudy? A sign that beer is not good for consumption is when it becomes cloudy (beer haze). Oxygen, which can enter into beer during the packaging process unless precautions are taken, is severely detrimental to its quality because it oxidizes components of beer, leading to staling and formation of haze.17 Beer oxygen content should be less than 0.1 mg/mL. Polyphenols are easiest to oxidize. Following their oxidation, polyphenols polymerize and cross-link with proteins to form insoluble complexes that cause turbidity.18 Beer can also
Experiments
Identification of ethanol in reaction with potassium dichromate in presence of sulfuric acid (SS, TD) Determination of alcohol by gas chromatography (TS) 607
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IS THE POPULARITY AND LONGEVITY OF BEER DUE TO IT HAVING A LOWER PRICE THAN THE OTHER ALCOHOLIC BEVERAGES? The students’ opinion was that the low price of beer contributed to its popularity but that its specific taste made it timeless.
become sour due to conversion of alcohol to acetic acid (unwanted fermentation). How to minimize beer spoilage? This beer topic should be expanded to describe its manufacturing and brewing, packaging, and storage. Cleanliness of the equipment and optimal use of cleaning aids should be discussed. Beer is a fat-free beverage. What is the effect of the presence of fat on foaming, for example, a greasy beer bottle? A discussion was led about the necessity of washing beer bottles with detergents and possible effects of residual detergents on foaming (i.e., the importance of thoroughly rinsing off the detergents). Further discussions involved topics on sterilization by pasteurization or sterile filtration,19 addition of food conservants (such as sodium benzoate, potassium sorbate, and ascorbic acid or vitamin C). Appropriate packaging can also minimize beer spoilage. Various beer containers were considered: glass bottles (dark color prevents light catalyzing oxidative reactions of beer components), aluminum cans, and plastic bottles (PET and Q-PACK used in some countries). Different containers were compared and their ability to allow or prevent light and oxygen in and carbon dioxide out of a container discussed.
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CONCLUSION The Beer Unit required participation of students before and during the chemistry class and laboratory. Availability of literature about beer enabled the students to find the facts necessary to create hypotheses about the causes for the popularity and longevity of beer. Using previously acquired chemical knowledge, the students selected experiments for the qualitative analysis of beer components (a majority of the experiments performed were proposed by students). Through the experiments and discussion, the students confirmed their hypotheses about the links between certain components of beer and its properties. Conclusions were drawn upon completion of the activities relating to certain properties of beer. They are summarized in the Table 1 (given in the Supporting Information). The analysis of the experimental results produced topics for further discussions enabling systematization and increase of knowledge of various areas of chemistry. At the same time, the importance and utility of learning chemistry was emphasized. All the results listed, together with increased interest and motivation of the students, made the Beer Unit useful in the chemistry teaching practice.
IS THE POPULARITY AND LONGEVITY OF BEER DUE TO THE PRESENCE OF SUBSTANCES ESSENTIAL FOR THE NORMAL FUNCTIONING OF OUR BODY?
Facts
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In addition to the beer components mentioned before, beer contains also about 210 mg/L of vitamins and provitamins. The vitamins included are B complex vitamins, vitamins H and E, and provitamin D2. Furthermore, there are a number of biologically active components (such as choline, lecithin, and αlipoic acid) directly involved in metabolic processes and numerous chemical reactions in the body. The individual concentrations of these compounds are as important as their mutual ratios.
ASSOCIATED CONTENT
S Supporting Information *
Uses of Scheme 1; student survey on attitudes and habits about beer; some interesting facts about beer; table with the conclusions from the unit. This material is available via the Internet at http://pubs.acs.org.
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Experiment
AUTHOR INFORMATION
Corresponding Author
Determination of emulsifying properties of beer. In two test tubes add 1 mL of water and 1 mL of cooking oil each. Add 0.5 mL of beer to the second test tube. Shake vigorously both test tubes and put them back on the stand. Observe. (TS, SD)
*E-mail:
[email protected].
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ACKNOWLEDGMENTS This article was supported by the Ministry for Science and Technological Development of the Republic of Serbia (Project No. 179048).
Topics for Further Discussion
Is beer an emulsifier for fats and oils and why?
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IS THE POPULARITY AND LONGEVITY OF BEER DUE TO THE PRESENCE OF PROTECTIVE FREE RADICAL SCAVENGERS?
REFERENCES
(1) Johnstone, A. H.; Wham, A. J. Chem. Educ. 1982, 3, 71−73. (2) Schmidt, M. H. J. Chem. Educ. 1997, 74, 393−395. (3) Goss, L. M. J. Chem. Educ. 2003, 1, 39−40. (4) Bamforth, Ch. W. Chem. Educator 2000, 5, 102−112. (5) Bamforth, Ch. W. Beer: Tap into the Art and Science of Brewing, 2nd ed.; Oxford University Press: New York, 2003. (6) Gillespie, B.; Deutschman, W. A. J. Chem. Educ. 2010, 87, 1244− 1247. (7) Palamand, S. R.; Aldenhoff, J. M. J. Agric. Food Chem. 1973, 21 (4), 536−536. (8) The beer unit would also be appropriate in the second year or upper levels of a university or college chemistry course in countries with fewer science courses at the secondary schools. (9) Taylor, D. G. Tech. Quart. Mast. Brew. Assoc. Am. 1990, 27, 131− 136. (10) Zumdahl, S. Introductory Chemistry: A Foundation, 5th ed.; Houghton Mifflin Co.: Boston, MA, 2004; p 463.
Facts
Beer contains polyphenols similar to red wine. It was suggested that barley polyphenols were more active than ones found in purple grapes. Polyphenols are very good free radical scavengers. Topics for Further Discussion
The structure−activity relation of polyphenols as free radical scavengers can be discussed. Also, results of interaction of free radicals with biomolecules should be discussed as well as condition of organisms in which free radicals are overproduced. Free radical scavengers present in various natural products should be listed and commented on. 608
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(11) Hillman, H. The New Kitchen Science; Houghton Mifflin Books: Boston, MA, 2003; p 178. (12) Harrington, R. J. Food and Wine Pairing: A Sensory Experience; John Wiley and Sons: Hoboken, NJ, 2007; pp 27−28. (13) Ramer, H. My Beer’s Too Hot, My Wine’s Too Cold, My Coke Is Just Right: There’s an Optimum Temperature for any Beverage. Houston Chronicle, June 23, 2008. http://www.chron.com/default/ article/My-beer-s-too-hot-my-wine-s-too-cold-my-Coke-is-1783574. php#page-2 (accessed Jan 2012). (14) The 48 Proof Beer. Beer Break, 2 (19). February 14, 2002 (http://www.realbeer.com/library/beerbreak/archives/ beerbreak20020214.php) (accessed Jan 2012). (15) Hanlon, M. Brewdog’s 55% ABV Beer: The Strongest and Most Expensive Beer in History. gizmag.com, July 22, 2010 (http://www. gizmag.com/brewdogs-55-abv-beer-the-strongest-and-most-expensivebeer-in-history/15798/) (accessed Jan 2012). (16) Schwarz, P. B.; Hill, N. S.; Rottinghaus, G. E. J. Am. Soc. Brew. Chem. 2007, 65, 1−8. (17) Bamforth, C. W.; Muller, R. E.; Walker, M. D. J. Am. Soc. Brew. Chem. 1993, 51, 79−88. (18) McMurrough, I.; Delcour, J. A. Fermentation 1994, 3, 175−182. (19) Goldammer, T. The Brewer’s Handbook, The Complete Book of Brewing Beer; 2nd ed.; Apex Publishers: Clacton on Sea, U.K., 2008, Chapter 17, Bottling Beer, Sterilization of Beer.
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