Eggs — Composition, Grading, Coagulation Temperatures, Foaming & Uses in Professional Cooking
Food Production · Part 4 · Module 14
Eggs — Composition, Grading, Coagulation Temperatures, Foaming & Uses in Professional Cooking
The egg is one of the most remarkable ingredients in the kitchen — emulsifier, aerator, thickener, binder, coating agent, and nutritional powerhouse all in one. Here is the complete science of eggs for professional cookery.
🥚 Structure of an Egg
Egg Components
Shell: Hard membrane of calcium carbonate and calcium phosphate. Provides structure. Colour varies by species (white, brown, pink, blue-green).
Membranes: Two semi-porous sheaths (outer + inner) under shell. Made of collagen proteins. Protective layer if shell cracks.
Egg White (Albumen/Glaire): 63% of egg fluid. Water:protein ratio = 9:1. Three layers: outer thin glair + middle thick glair + inner thin glair. Contains albumins, mucoproteins, globulins. Nearly 0% fat, <0.5% carbohydrate.
Yolk: 1/7th protein + 1/4th fat + rest water. Contains phosphorus, calcium, iron. Held at centre by chalazae (protein threads). Yellow pigment = xanthophyll/Lutein (richest pigment in yolk).
Vitelline Membrane: Sheath separating yolk from white. Weakens as egg ages.
Air Cell: Between membranes at round end. Expands as egg ages (larger air cell = older/lower quality egg).
Blastodisc/Germinal Disc: Circular white spot (1–2mm) on external of yolk.
Membranes: Two semi-porous sheaths (outer + inner) under shell. Made of collagen proteins. Protective layer if shell cracks.
Egg White (Albumen/Glaire): 63% of egg fluid. Water:protein ratio = 9:1. Three layers: outer thin glair + middle thick glair + inner thin glair. Contains albumins, mucoproteins, globulins. Nearly 0% fat, <0.5% carbohydrate.
Yolk: 1/7th protein + 1/4th fat + rest water. Contains phosphorus, calcium, iron. Held at centre by chalazae (protein threads). Yellow pigment = xanthophyll/Lutein (richest pigment in yolk).
Vitelline Membrane: Sheath separating yolk from white. Weakens as egg ages.
Air Cell: Between membranes at round end. Expands as egg ages (larger air cell = older/lower quality egg).
Blastodisc/Germinal Disc: Circular white spot (1–2mm) on external of yolk.
📏 Egg Size Classification
| Grade | Weight per egg | Per Dozen |
|---|---|---|
| Jumbo | 75g | 860g |
| Extra Large | 65–70g | 764g |
| Medium | 49g | 598g |
| Small | 42g | 520g |
| Peewee | 40g | 436g |
🏆 Egg Grades
Grade AA
Clean, unbroken. Yolk: firm, well-centred, round. Large proportion of thick white to thin. Small air cell. Freshest quality. Floats in water = bad (so AA: sinks).
Grade A
Covers relatively small area. Yolk fairly centred, round and upstanding. Slightly larger air cell than AA.
Grade B
Spreads more. Yolk flattened. More thin white than thick white. Clean to slightly stained shell. Largest air cell.
🌡️ Coagulation Temperatures
Egg Protein Coagulation
Egg White: 60–65°C (140–149°F)
Egg Yolk: 62–70°C (144–158°F)
Whole Egg (beaten): ~69°C (156°F)
Custard (whole egg + liquid): 78–86°C (176–187°F)
White coagulates before yolk — that’s why we can achieve set white + runny yolk (poached, fried egg).
Green ring in hard-boiled eggs: Caused by high heat or prolonged cooking — iron (yolk) + sulphur (white) → iron sulphide (green, strong aroma). Prevention: cook at low heat, short time, cool immediately.
Egg Yolk: 62–70°C (144–158°F)
Whole Egg (beaten): ~69°C (156°F)
Custard (whole egg + liquid): 78–86°C (176–187°F)
White coagulates before yolk — that’s why we can achieve set white + runny yolk (poached, fried egg).
Green ring in hard-boiled eggs: Caused by high heat or prolonged cooking — iron (yolk) + sulphur (white) → iron sulphide (green, strong aroma). Prevention: cook at low heat, short time, cool immediately.
🧪 Egg Freshness Tests
3 Tests for Freshness
1. Water Test: Fresh (good) egg = sinks · Old (bad) egg = floats
2. Spread/Break Test: Good egg = thick white, yolk centred, round and high · Bad egg = thin watery white, flat broad yolk
3. Candle Test: Hold against candle flame: Good egg = opaque · Air cell size visible (smaller = fresher)
2. Spread/Break Test: Good egg = thick white, yolk centred, round and high · Bad egg = thin watery white, flat broad yolk
3. Candle Test: Hold against candle flame: Good egg = opaque · Air cell size visible (smaller = fresher)
🍳 Uses of Eggs in Cooking
7 Functional Uses of Eggs
1. Emulsifying agent: Lecithin in yolk stabilises oil-water emulsions (mayonnaise, Hollandaise)
2. Aerating agent: Beaten egg whites create foam that leavens soufflés, sponge cakes, meringues
3. Thickening agent: Proteins coagulate when heated — used in custards, sauces (liaison)
4. Binding agent: Holds ingredients together in burger patties, meatloaf, croquettes
5. Coating agent: Egg wash creates golden crust on breaded items
6. Clarifying agent: Egg whites clarify consommé (attract impurities as they coagulate)
7. Glazing agent: Egg wash applied before baking gives shine
2. Aerating agent: Beaten egg whites create foam that leavens soufflés, sponge cakes, meringues
3. Thickening agent: Proteins coagulate when heated — used in custards, sauces (liaison)
4. Binding agent: Holds ingredients together in burger patties, meatloaf, croquettes
5. Coating agent: Egg wash creates golden crust on breaded items
6. Clarifying agent: Egg whites clarify consommé (attract impurities as they coagulate)
7. Glazing agent: Egg wash applied before baking gives shine
Foam Rules (for beating egg whites)
• Yolk reduces foaming — separate completely before beating
• Weak acids (lemon juice, cream of tartar) increase foam stability — use 1 tsp cream of tartar per 500g whites
• Whites foam best at room temperature — take out of fridge 1.5 hrs before beating
• Never overbeat — overbeaten whites look dry and curdled (lose leavening power)
• Sugar added during beating improves foam stability (for soufflés and meringues)
• Weak acids (lemon juice, cream of tartar) increase foam stability — use 1 tsp cream of tartar per 500g whites
• Whites foam best at room temperature — take out of fridge 1.5 hrs before beating
• Never overbeat — overbeaten whites look dry and curdled (lose leavening power)
• Sugar added during beating improves foam stability (for soufflés and meringues)
🎯 UGC NET Key Points — Part 4 Module 14
◆ Egg white = 63% of egg’s fluid content · Water:protein = 9:1 ratio
◆ Chalazae = protein threads holding yolk at centre
◆ Lutein = richest pigment in egg yolk (xanthophyll family)
◆ Air cell: larger = older/lower quality egg
◆ Grade AA = smallest air cell (freshest) · Grade B = largest air cell
◆ Egg white coagulates: 60-65°C · Egg yolk: 62-70°C · Custard: 78-86°C
◆ White coagulates before yolk → enables set-white, runny-yolk dishes
◆ Green ring in boiled eggs: iron + sulphur → iron sulphide (overcooking)
◆ 7 culinary functions: Emulsifier, Aerator, Thickener, Binder, Coating, Clarifier, Glaze
◆ Lecithin in egg yolk = emulsifying agent (for mayonnaise, Hollandaise)
◆ Good egg: sinks in water · Bad egg: floats in water
◆ Chalazae = protein threads holding yolk at centre
◆ Lutein = richest pigment in egg yolk (xanthophyll family)
◆ Air cell: larger = older/lower quality egg
◆ Grade AA = smallest air cell (freshest) · Grade B = largest air cell
◆ Egg white coagulates: 60-65°C · Egg yolk: 62-70°C · Custard: 78-86°C
◆ White coagulates before yolk → enables set-white, runny-yolk dishes
◆ Green ring in boiled eggs: iron + sulphur → iron sulphide (overcooking)
◆ 7 culinary functions: Emulsifier, Aerator, Thickener, Binder, Coating, Clarifier, Glaze
◆ Lecithin in egg yolk = emulsifying agent (for mayonnaise, Hollandaise)
◆ Good egg: sinks in water · Bad egg: floats in water