Vol. XXXIV · History and Projects Plate 8 of 13project, hollandaise, emulsion, egg yolk, butter, dispersed phase, volume fraction, viscosity, Krieger–Dougherty, holding temperature, curdling, breaking, design briefMT

Project: A Sauce That Holds.

One yolk can hold far more butter than most recipes use — until the droplets are packed so tightly that a little more breaks the sauce.

A hollandaise is an emulsion of butterfat droplets in the water of the yolk and the lemon (X.2, X.5). Its thickness comes from crowding: as the volume fraction of fat rises, the droplets jostle and the viscosity climbs steeply, toward infinity as they approach packing (X.3, Krieger–Dougherty). Thick is good — but near packing the sauce is fragile: a few more grams of butter, or a little evaporation, and the droplets merge and the sauce breaks. Adding a spoonful of water or lemon juice brings it back from the edge.

Temperature is the other half (X.5). Below about 35 °C the butterfat sets and the sauce turns stiff and greasy; between about 60 and 80 °C the yolk proteins thicken and stabilise it; past about 85 °C they curdle into scrambled egg. Your design: grams of butter per yolk, grams of water or lemon juice, and the holding temperature. The starting design — a lot of butter, little water, held too hot — fails.

Below: the sauce's fat fraction and relative thickness for your design (course emulsion bench, Krieger–Dougherty), its state at the holding temperature, and the brief.

What you will learn
Workshop
Course emulsion bench, per large egg yolk (about 8.5 g of water): butter 82 % fat (density 0.91) and 16 % water; fat volume fraction from these; thickness relative to water from Krieger–Dougherty (maximum packing about 0.71); state at the holding temperature from the course yolk model. Brief: smooth at the holding temperature (index 0.9 or more), fat fraction 0.68 or less, thickness at least 10 times water.

Thick, but not packed

At 100 g of butter per yolk with 10 g of water, the fat fraction is 0.72 — almost packed. The sauce is very thick but one step from breaking; adding 15 g more water brings it to 0.65, still about 71 times as thick as water. Classic recipes use about 50–75 g of butter per yolk, comfortably below packing, and the course's solution — 60 g of butter, 15 g of water or lemon, held at 65 °C — sits in the middle of every check.

At the stove: whisk the yolk with the water or lemon over gentle heat until it thickens and the whisk leaves a trail (about 65–70 °C); off the heat, whisk in warm melted or cold diced butter little by little; season; keep the sauce warm over water at about 60–65 °C, never boiling. If it thickens too much, whisk in a teaspoon of warm water; if it breaks, start a fresh yolk with a spoonful of water and whisk the broken sauce into it slowly (X.4).

At the stove

Make hollandaise with one yolk and weigh the butter. Keep adding until it feels very stiff, then add a teaspoon of water and watch it loosen.

A single yolk has been used to emulsify well over a litre of oil in kitchen experiments: the limit is not the lecithin, which is plentiful, but the water — with too little continuous phase the droplets have nowhere to go.

Terms

Fat fraction
The share of the sauce's volume that is fat droplets.
Packing
The fraction at which droplets touch and cannot crowd further.
Holding temperature
The temperature at which the sauce waits for service.
Breaking
Droplets merging so the fat separates.
A warm butter sauce holds when its fat fraction stays below packing (≈ 0.68 or less) yet thick (≥ 10 × water) and is kept at 60–80 °C. Add water to pull it back from breaking; never let it boil.

Sources

  1. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.