Chapter 14 Quiz — Eggs

A mix of recall, application, and explanatory questions. The answer key follows after question 18.

Multiple Choice (15 questions)

1. The protein responsible for the bulk of an egg white's "set" texture in a fully cooked egg is:

A. Ovotransferrin (conalbumin) B. Ovomucoid C. Ovalbumin D. Lysozyme

2. At approximately what temperature does the yolk's water-soluble proteins begin to set, allowing a "soft, creamy yolk" texture in a sous-vide egg?

A. 50°C (122°F) B. 65°C (149°F) C. 80°C (176°F) D. 95°C (203°F)

3. The gray-green ring around the yolk of an overcooked hard-boiled egg is:

A. Mold contamination from a cracked shell B. Iron sulfide formed from iron in the yolk and sulfur in the white C. Oxidized cholesterol D. Carotenoid pigment migration

4. Mayonnaise is structurally:

A. A fat dispersed in water (an oil-in-water emulsion) B. A water dispersed in fat (a water-in-oil emulsion) C. A protein gel D. A solid suspension of egg in oil

5. Older eggs (about a week old) peel more easily than brand-fresh eggs because:

A. The shell has thinned with age B. The white's pH has risen, weakening the bond between white and inner shell membrane C. The yolk has shrunk away from the white D. Bacteria have begun digesting the membrane

6. Vinegar in poaching water helps the egg white set quickly because:

A. The acid raises the temperature at which proteins denature B. The acid lowers the pH around the egg, accelerating coagulation of certain white proteins C. The vinegar kills surface bacteria on the egg D. The vinegar adds volume to the water

7. Cream of tartar is added to whipped egg whites to:

A. Increase the foam's volume B. Sweeten the foam slightly C. Slow disulfide-bond cross-linking and widen the over-whipping window D. Speed up protein denaturation

8. Aquafaba (chickpea liquid) can replace egg whites in meringue because:

A. It contains the same proteins as egg whites B. It contains chickpea proteins and saponins that act as foam stabilizers analogous to egg-white proteins C. It is naturally pH-acidic, like egg whites D. It is sweetened during processing

9. A crème anglaise (pourable custard) typically thickens at:

A. 60–65°C / 140–149°F B. 82–85°C / 180–185°F C. 100°C / 212°F (just simmering) D. 105°C / 221°F (must be held at boil)

10. Lecithin in egg yolk is chemically a:

A. Carbohydrate B. Phospholipid C. Amino acid D. Carotenoid pigment

11. Brioche differs from a plain water-flour-yeast bread principally because the egg's:

A. Yolk fat lubricates and tenderizes the gluten network B. White provides additional sugar C. Whole egg increases the loaf's salt content D. Shell membrane stays in the dough as fiber

12. A French rolled omelette differs from a Spanish tortilla española primarily in:

A. The presence of eggs (only one uses them) B. Cooking time and temperature: short and high vs. long and slow C. The type of pan used (only one is acceptable in copper) D. Whether the eggs are pasteurized

13. Italian meringue is more stable than French meringue because:

A. It uses larger eggs B. The hot sugar syrup partially cooks the proteins as it is poured into the whipping whites C. It contains more sugar relative to whites D. It is whipped in a larger bowl

14. Salmonella in commercial eggs is most often introduced:

A. Through the chicken's reproductive tract before the shell forms B. By contamination during washing C. Through cracks in the shell after laying D. By feed contamination

15. A chia "egg" (1 tbsp ground chia + 3 tbsp water) is a useful substitute for an egg in baked goods primarily because:

A. It mimics yolk lecithin's emulsifying ability B. The chia seeds release polysaccharide mucilage that thickens water into a viscous gel and acts as a binder C. It is naturally rich in cholesterol D. It contains the same proteins as egg whites in lower concentration

Short Answer (4 questions)

16. Explain, in 4–6 sentences, why temperature matters more in egg cookery than in most other ingredients. Reference at least two specific egg-white proteins and their setting temperatures.

17. A reader's mayonnaise has broken — it looks like oily liquid sitting in oily liquid, no thick emulsion forming. Walk through, in step-by-step instructions, how they should fix it. Explain the chemistry of why your fix works.

18. A reader wants to make perfect hard-boiled eggs that peel cleanly. Their grocery-store eggs are typically less than three days old when they buy them. What two things would you tell them to do, and what is the chemistry behind each?

Answer Key

1. C — Ovalbumin. Ovalbumin is about 54% of the white's protein content and sets around 80°C; it is the structural workhorse of a fully set white. Ovotransferrin sets earlier (~62°C); lysozyme is an enzyme not a structural protein; ovomucoid contributes to digestion-resistance more than to set texture.

2. B — 65°C (149°F). The yolk's water-soluble proteins begin setting at about 65°C, which is why this temperature window produces the "creamy yolk, soft-set white" texture of a properly slow-cooked egg.

3. B — Iron sulfide. At high heat (above ~90°C / 194°F), iron from the yolk reacts with hydrogen sulfide produced from sulfur-containing white proteins to form iron sulfide (FeS), a gray-green compound. It's harmless but indicates overcooking.

4. A — Oil-in-water emulsion. Mayonnaise is microscopic oil droplets dispersed in a small amount of water (vinegar or lemon juice), with each droplet coated by yolk lecithin and proteins. The "macroscopic feel" is creamy because the droplets are small and densely packed; the chemistry is oil-in-water.

5. B — pH rise. As eggs age, CO₂ slowly diffuses out through the shell pores. The white's pH rises from about 7.6 (fresh) to over 9 (old). At higher pH, the white binds less tightly to the inner shell membrane, releasing during peeling.

6. B — Acid speeds coagulation. Lysozyme and ovotransferrin coagulate faster at lower pH. The acid drops the pH around the egg as it enters the water, helping the white set quickly into a coherent shape rather than spreading into wispy strings.

7. C — Slow disulfide cross-linking. Cream of tartar (an acid) slows the rate at which cysteine residues on neighboring proteins form intermolecular disulfide bonds. This widens the time window between "stiff peaks" and "over-whipped, brittle, weeping" — a more forgiving foam to make.

8. B — Saponins and chickpea proteins. Aquafaba contains a mix of chickpea albumins and globulins plus small amounts of saponins (natural surfactants). These different molecules play roles analogous to egg-white proteins — they migrate to bubble surfaces, stabilize foam, and lock structure during baking.

9. B — 82–85°C / 180–185°F. Below 75°C, custard proteins haven't set. Above 88°C, they curdle into visible lumps. The 80–85°C window is the safe zone where the proteins form a fine network without breaking.

10. B — Phospholipid. Lecithin is mostly phosphatidylcholine, a phospholipid with a hydrophilic phosphate head and two hydrophobic fatty-acid tails. This dual nature is what makes it an excellent emulsifier — it bridges water and oil.

11. A — Yolk fat lubricates gluten. Yolk fat coats and lubricates the gluten network, preventing the strong, elastic gluten formation of plain bread. This produces brioche's softer, cake-like crumb.

12. B — Cooking time and temperature. A French rolled omelette is cooked in roughly 90 seconds at high heat with constant agitation, kept baveuse (slightly underdone) inside. A Spanish tortilla española is slow-cooked into a thick disk for many minutes, with potatoes and onions, and is closer to a frittata than to an omelette.

13. B — Hot syrup partially cooks the proteins. When 118°C sugar syrup hits whipping whites, the heat partially denatures the proteins as it is incorporated. The denatured proteins form a more permanent foam structure than raw whites, giving Italian meringue hours of stability versus French meringue's rapid weeping.

14. A — Reproductive tract. Most Salmonella contamination of commercial eggs occurs before the shell forms — the bacteria infect the chicken's reproductive tract and end up inside the egg. This is why even a clean shell can be a risk; the contamination is internal, not surface.

15. B — Mucilage. Chia seeds contain soluble polysaccharide mucilage on their seed coats; in water, this mucilage hydrates into a viscous gel that physically holds dough together (binding) much like egg proteins do. It does not, however, emulsify, foam, or leaven — chia eggs are binders, not full egg replacements.

16. Sample answer. Different egg-white proteins denature at different temperatures, so a single egg passes through several distinct textural states as it heats. Ovotransferrin sets first (around 62°C / 144°F), causing the white to begin clouding while still mostly liquid. Ovalbumin (the bulk of the white at about 54% of protein content) sets fully at 80°C, producing a firm white. The yolk's proteins set in a separate window starting around 65°C. Because these temperatures are 5–20°C apart, a degree-or-two change in cooking temperature changes which proteins are set and which are still liquid, which changes the texture dramatically. In contrast, a roasted potato or seared steak is far less sensitive to single-degree temperature changes — the egg's multi-protein system makes it uniquely temperature-precise.

17. Sample answer. (1) In a clean bowl, place one fresh egg yolk and a teaspoon of mustard. Whisk for 30 seconds to mix. (2) Drizzle the broken mayonnaise as if it were oil — drop by drop at first, whisking continuously, then in a thin stream as the new emulsion forms. (3) Continue whisking until all the broken mayo is incorporated; the new mayonnaise will be thick, glossy, and stable. Why this works: the broken mayonnaise contains all the oil and acid you need, but the original yolk's emulsifier population was overwhelmed when oil was added too fast. Starting fresh with another yolk supplies new lecithin and proteins to coat each oil droplet; adding the broken mayonnaise slowly gives the new emulsifier time to coat the new oil before droplets coalesce.

18. Sample answer. (1) Buy the eggs and let them rest in the refrigerator for a week before hard-boiling. As eggs age, the white's pH rises (CO₂ diffuses out through the shell), which weakens the white-to-membrane bond and allows clean peeling. (2) After cooking, transfer the eggs immediately to ice water. The thermal shock causes the white to contract slightly inside the shell, breaking small adhesions; the fresh interior temperature drop also halts overcooking and the formation of the iron-sulfide gray ring. Together, these two steps address the two main causes of poor peeling: a freshly-laid egg's tight white-to-membrane bond, and a still-hot egg's residual stickiness.