Chapter 21 — Quiz

Mix of recall, application, and "explain why" questions. Answer key with explanations at the bottom.

Multiple choice (15 questions)

1. All of the following teas come from the same plant species (Camellia sinensis) EXCEPT:

a) Green tea b) Oolong tea c) Pu-erh tea d) Yerba mate

2. The single chemical event that distinguishes a green tea from a black tea is:

a) Microbial fermentation b) Enzymatic oxidation of polyphenols c) Caramelization of leaf sugars d) Fluorescence of chlorophyll

3. Recommended water temperature for brewing a delicate Japanese green tea (sencha) is approximately:

a) 60°C / 140°F b) 75–80°C / 167–176°F c) 95–100°C / 203–212°F d) The hotter the better

4. Cup of black tea steeped for one minute, compared to a cup steeped for four minutes, will contain:

a) Substantially less caffeine and substantially less tannin b) Approximately the same caffeine but substantially less tannin c) Substantially less caffeine but the same tannin d) Both at the same level

5. Coffee that tastes sour is typically:

a) Over-extracted b) Under-extracted c) Brewed at too high a temperature d) Made with stale beans

6. The pressure used in a typical espresso machine is approximately:

a) 1 bar (atmospheric) b) 3 bar c) 9 bar d) 50 bar

7. The two species of Coffea in major commercial use are:

a) Coffea arabica and Coffea canephora (robusta) b) Coffea arabica and Camellia sinensis c) Coffea ethiopica and Coffea brasiliensis d) Coffea arabica and Coffea liberica

8. A "shaken" cocktail differs from a "stirred" cocktail in all of the following ways EXCEPT:

a) Shaking introduces air, producing a slightly cloudy and frothy texture b) Shaking dilutes more, because tumbling ice sheds water faster c) Shaking cools the drink faster d) Shaking changes the alcohol concentration of the spirit itself

9. Wine's malolactic fermentation:

a) Is performed by Saccharomyces cerevisiae b) Is performed by lactic-acid bacteria, typically Oenococcus oeni c) Converts ethanol back to sugar d) Increases the wine's tartness

10. Henry's law predicts that as the temperature of a sparkling beverage rises:

a) The dissolved CO₂ concentration increases b) The dissolved CO₂ concentration stays the same c) The dissolved CO₂ concentration decreases d) The CO₂ separates from the water by phase change

11. The Mentos-and-Diet-Coke geyser is primarily caused by:

a) A chemical reaction between Mentos ingredients and the soda's acid b) The candy heating the soda above its boiling point c) The candy's microscopically rough surface providing many nucleation sites for dissolved CO₂ d) The aspartame in Diet Coke specifically reacting with the candy

12. The traditional sour cocktail formula (whiskey sour, daiquiri, margarita) is approximately:

a) 1:1:1 spirit : sour : sweet b) 2:1:0.75 spirit : sour : sweet c) 1:2:1 spirit : sour : sweet d) 3:1:1 spirit : sour : sweet

13. The current scientific consensus (as of 2023) on the health effects of moderate alcohol consumption is best summarized as:

a) Moderate consumption clearly extends life expectancy b) Moderate consumption is neutral c) There is no level of alcohol consumption that improves health d) Moderate red wine consumption is uniquely beneficial

14. A roast that best preserves a coffee bean's origin character is:

a) A very dark roast, well past second crack b) A medium roast, just at second crack c) A light roast, shortly after first crack d) A green (unroasted) bean

15. Yerba mate originates with the:

a) Inca peoples of Peru b) Mapuche peoples of Chile c) Guaraní peoples of what is now Paraguay, Argentina, and southern Brazil d) Aztec peoples of central Mexico

Short answer (5 questions)

16. Explain in 3–5 sentences why a very fine grind is necessary for espresso but inappropriate for French press, using the language of extraction kinetics.

17. A friend complains that her open bottle of champagne went flat overnight despite being recapped with a stopper and stored on the counter. Identify two physical changes she could have made (without buying new equipment) that would have substantially extended its carbonation, and explain why each works.

18. Pat is preparing a chemistry-class demonstration on tea extraction. She wants the visual difference between a "right temperature" cup and a "too-hot" cup to be as dramatic as possible for a class audience. Which type of tea (and why) should she choose for the demonstration?

19. Maya is brewing chamomile tea for her cousin's daughter at bedtime. Her chamomile cup tastes weak and watery even after a 5-minute steep with very hot water. Other than buying fresher chamomile, what is one structural change she could make to extract more flavor from the same flowers?

20. Aroon has switched his restaurant's house margarita to use a single 4 cm cube of frozen lime juice in place of plain water ice. Explain in chemistry terms what this change does to the cocktail's evolution from first sip to last sip.

Answer key

1. d) Yerba mate is Ilex paraguariensis, a holly relative — not Camellia sinensis. It is technically a tisane.

2. b) Enzymatic oxidation of polyphenols by polyphenol oxidase. Green tea has this enzyme inactivated immediately by heat (steaming or pan-firing); black tea allows it to fully oxidize the leaf. Pu-erh involves microbial fermentation, but standard black tea does not — calling black tea "fermented" is inaccurate, despite being a common usage.

3. b) 75–80°C / 167–176°F. Hotter water extracts a flood of tannins from delicate green tea, overwhelming the gentle floral compounds.

4. b) Approximately the same caffeine but substantially less tannin. Caffeine is a small, highly water-soluble molecule that diffuses out of leaves quickly — most is in the cup within 60–90 seconds. Tannins are larger and slower-diffusing, continuing to extract over several minutes. Short-steep teas are less bitter, but the caffeine reduction is minimal.

5. b) Under-extracted. Sour, acidic compounds extract first; if extraction stops early (too coarse a grind, too short a contact time, too cool water), you get the acids without the sugars and Maillard products that balance them.

6. c) 9 bar (about 130 psi). This is roughly 9 times atmospheric pressure.

7. a) Coffea arabica (about 60% of world production, more nuanced flavor, lower caffeine) and Coffea canephora (robusta, about 40%, more caffeine, more bitter).

8. d) Shaking does not change the alcohol concentration of the spirit. It introduces air, dilutes more (more melt), and cools faster — but the spirit's percentage alcohol doesn't change; only the dilution does.

9. b) Lactic-acid bacteria (Oenococcus oeni primarily). MLF converts malic to lactic acid plus CO₂, softening the wine's acidic profile.

10. c) The dissolved CO₂ concentration decreases. Henry's law constant for CO₂ in water increases with temperature, meaning less gas can be held in solution at higher temperatures.

11. c) The candy's microscopically rough surface provides countless nucleation sites for already-dissolved CO₂ to come out of solution. The reaction is physical, not chemical.

12. b) 2:1:0.75. Roughly 60 mL spirit : 30 mL citrus : 22 mL syrup.

13. c) There is no level of alcohol consumption that improves health. The 2023 JAMA Network Open analysis, the WHO, and the Canadian Centre on Substance Use and Addiction all reached this conclusion. Earlier "moderate drinking is good for you" claims were largely an artifact of confounded comparison groups in observational studies.

14. c) A light roast, shortly after first crack. The further into the roast you go, the more the cup is dominated by Maillard end-products and pyrolysis flavors, which mask origin character.

15. c) The Guaraní peoples. Mate's preparation tradition (the gourd, the bombilla straw, the shared circulation) is Indigenous to that region.

16. (Short answer.) Espresso uses a very fine grind because the contact time between water and grounds is extremely short — roughly 25–30 seconds — and only a fine grind has enough surface area for sufficient extraction in that window. The pressure (~9 bar) forces water through a bed too fine to drain by gravity. A French press, by contrast, uses a coarse grind and a 4-minute immersion: the longer contact time more than compensates for the lower surface area, and a fine grind in a French press would over-extract heavily and pass fines through the metal mesh. The principle: extraction depends on grind size and contact time and temperature and pressure, and different brew methods balance these levers differently.

17. (Short answer.) First, refrigerating the bottle: lower temperature increases the Henry's law constant for CO₂, so the cold liquid can hold more dissolved gas. Second, transferring the wine to a smaller bottle (or keeping the original full): minimizing the headspace above the liquid means less volume for CO₂ to escape into before reaching a new partial-pressure equilibrium. (A silver spoon in the bottle does not work — that's folklore.)

18. (Short answer.) A delicate green tea (Japanese sencha or Chinese long jing/dragonwell). The difference between a 75°C cup and a 100°C cup is far more visually and aromatically dramatic with green tea than with black tea, because the tannins in green tea spike sharply at high temperatures while a robust black tea is comparatively forgiving. Cheap, broken-leaf grocery-store green tea actually shows the effect more strongly than premium whole leaf — the broken cells extract faster — making it a good choice for a class budget.

19. (Short answer.) Crush or roughly grind the chamomile flowers before brewing. The flavor compounds are tucked inside the flower's hard structures (the seed-like centers especially) and need surface-area help to come out. By Fick's law, smaller particle size dramatically reduces extraction time. A mortar-and-pestle press of the flowers, or even a brief tear with the fingers, makes a noticeably stronger cup. Alternative: brew in a covered vessel (a teapot rather than an open mug) so volatile compounds aren't lost to evaporation.

20. (Short answer.) A standard ice cube melts and dilutes the drink with plain water — over time, the cocktail becomes less concentrated in everything (lime, alcohol, salt). A frozen-lime-juice cube melts and intensifies the lime: each sip carries more lime acid as the cube dissolves, while the alcohol concentration drops but more slowly than with plain water. The first sip of the drink is more spirit-forward; the last is more citrus-forward. The technique is using ice as a flavor-modifying ingredient rather than a neutral coolant — a sophisticated extension of the principle that ice is a thermodynamic and chemical actor, not just a cooling agent.