Vol. XVII · Eggs and Dairy Plate 5 of 10custard, crème anglaise, crème caramel, baked custard, water bath, bain-marie, 蒸蛋, steamed egg, curdling, setting temperature, dilutionHT

Custards.

Steamed egg (蒸蛋) at full steam turns into a honeycomb of holes; with the lid ajar and the heat low, it sets like silk.

Custards thicken a liquid with egg. In a pouring custard (crème anglaise) the eggs are stirred over heat until the sauce coats a spoon, near 80 °C, and taken off before it curdles at around 85 °C. In a set custard — crème caramel, flan, Japanese chawanmushi, Chinese 蒸蛋 — the mixture is left still and the proteins link into a gel through the whole dish. Diluting eggs with milk, cream or water separates the protein molecules, so they need a higher temperature to meet and link, and they set more softly; sugar raises the setting point further.

The enemy is uneven heat. If the outside of a set custard gets much hotter than its setting point, the proteins there over-tighten, squeeze out liquid and trap steam bubbles: curdled, holey, weeping. So custards are baked in a water bath (bain-marie), which holds the dish's surroundings near 100 °C at most, or steamed gently with the lid ajar or the dish covered. The workshop sets a steamed egg custard.

Below: the setting and curdling temperatures of an egg custard against its dilution with liquid and sugar (teaching curves shaped on common custard practice), and whether steaming at the temperature you choose will curdle it.

What you will learn
Workshop
Teaching model: undiluted egg sets near 70 °C; each part of liquid per part of egg raises the setting point by about 4 °C, and sugar by about 0.2 °C per percent; curdling and bubbling about 12 °C above the setting point. Gentle steaming (lid ajar) holds the steam around the dish near 85–90 °C; full steam at 100 °C.

Even, gentle heat

For 蒸蛋 with one and a half parts of water to one of egg, this teaching model sets the custard near 76 °C and puts curdling near 88 °C. Full steam at 100 °C is well above that, so the outer layers overheat and bubble before the middle sets: the honeycomb texture. Lowering the heat, leaving the lid ajar or covering the dish with a plate keeps the surroundings nearer 85–90 °C and the custard smooth. A pouring custard of milk, yolks and sugar sets near 84 °C, which is why crème anglaise is taken to about 80 °C and no further.

Methods. For 蒸蛋: beat eggs with 1.5–2 times their volume of warm stock or water and a pinch of salt; strain through a sieve and skim the foam; cover the bowl with a plate or film; steam over low heat for 10–15 minutes until it just trembles; finish with soy sauce and sesame oil. For crème caramel: pour into caramel-lined moulds, set in a roasting tin of hot water, bake at about 150 °C until set at the edges and wobbly in the middle. For crème anglaise: heat milk, whisk it into yolks and sugar, stir over low heat until it coats a spoon, and strain into a cold bowl.

At the stove

Make two small bowls of 蒸蛋 from the same mixture. Steam one uncovered over high heat and one covered with a plate over low heat. Cut into both: holes against silk.

Japanese chawanmushi and Chinese 蒸蛋 are close cousins, both custards of egg and stock steamed in small cups; chawanmushi usually adds prawn, chicken, ginkgo nuts and mushroom.

Terms

Custard
A liquid thickened and set by egg proteins.
Bain-marie
A water bath that keeps a dish's surroundings at or below 100 °C.
Crème anglaise
A pouring custard of milk, yolks and sugar.
蒸蛋
Chinese steamed egg custard.
Dilution and sugar raise the setting temperature; custards curdle about 12 °C above it. Use a water bath or gentle steam so the outside never runs far ahead.

Sources

  1. Egg proteins: ovotransferrin sets near 62 °C, ovalbumin near 80 °C, the yolk thickens near 65 °C and sets near 70 °C (H. McGee, On Food and Cooking, 2004, ch. 2; P. Barham, The Science of Cooking, 2001).
  2. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
  3. H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.