Vol. VIII · Browning Plate 4 of 9caramelisation, Maillard, sugar, amino acids, temperature, flavour, diacetyl, "caramelised" onionsMF

Caramelisation Is Not Maillard.

"Caramelised onions" are mostly Maillard browning. Real caramelisation of sucrose needs a pan some forty degrees hotter.

Two browning reactions are often confused. Caramelisation is what sugar does alone when heated hard enough: the molecules dehydrate and break apart, giving buttery diacetyl, fruity esters, toasty furans, sharp acids and, as it goes on, bitterness and brown caramel polymers. Maillard browning needs sugars and amino acids together and makes the savoury, roasted and meaty notes (VIII.1).

The two run at different temperatures. Sucrose caramelises fast only above about 170 °C; glucose and especially fructose start lower. Maillard browning, given amino acids, is quick from about 130 °C. So most browning in savoury cooking — meat, bread crust, onions, toasted nuts — is Maillard, and true caramelisation belongs to sugar work (VII.8) and the sugary tops of desserts. The workshop puts the two rates on one chart.

Below: minutes to golden against surface temperature for Maillard browning and for sucrose caramelisation (course parameters), on a logarithmic scale.

What you will learn
Workshop
Course parameters: Maillard browning 0.30 per minute at 150 °C, activation energy 125 kJ/mol; sucrose caramelisation 0.04 per minute at 170 °C, 150 kJ/mol. Fructose and glucose caramelise at lower temperatures than sucrose.

Two reactions, two temperatures

To reach golden in ten minutes, Maillard browning needs a surface near 133 °C in this model; sucrose caramelisation needs about 176 °C, some 43 degrees hotter. At 160 °C a Maillard surface is golden in 1 min while sucrose would take 44 min. A pan of onions at 120–130 °C is therefore browning by Maillard, helped by their glucose and fructose, which caramelise far more easily than sucrose; "caramelised onions" is a cook's name, not a chemist's.

Knowing which reaction is running tells you what to expect. A crème brûlée top, sugar-dusted puff pastry and spun sugar are caramelisation: blast heat, pure sugar, bitter-sweet at the end. A roast, a crust, toasted bread and roasted coffee are Maillard: protein and sugar together, savoury and roasted. Dulce de leche, milk jam and Chinese 拔丝 dishes have both at once — milk proteins with sugar, and hot sugar syrup over fried pieces.

At the stove

Heat a spoonful of plain sugar in a dry pan until amber and taste it; then toast a spoonful of milk powder in another pan until the same colour and taste that. The first is caramel; the second, Maillard: buttery and bitter against biscuity and savoury.

Fructose begins to caramelise near 110 °C, glucose near 160 °C and sucrose near 160–170 °C; that is why honey, rich in fructose, browns quickly in cakes (VII.9).

Terms

Caramelisation
The breakdown of sugar alone under strong heat.
Diacetyl
A buttery-smelling compound made by caramelisation (and by some bacteria in butter).
拔丝
A Chinese dessert method: fried pieces tossed in hot sugar syrup that pulls into threads.
Dulce de leche
Milk and sugar cooked slowly until browned: both reactions together.
Caramelisation is sugar alone above about 170 °C; Maillard is sugar with amino acids and runs some forty degrees lower.

Sources

  1. Maillard browning: apparent activation energies of roughly 100–160 kJ/mol are reported for colour formation (M. A. J. S. van Boekel, Kinetic Modeling of Reactions in Foods, CRC Press, 2009). The course uses 125 kJ/mol and a teaching scale of browning.
  2. H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.