How Browning Works: Maillard Reaction and Caramelization
Filed under Caramels
Brown food tastes better, and two chemical reactions do most of the work. The first is a reaction between proteins and sugars that runs fastest above the boiling point of water and produces the crust on a steak, the color of bread, the smell of coffee and the flavor of chocolate. The second is what sugar does on its own when it gets hot enough, which produces caramel and the top of a crème brûlée. Cooks call both "browning", but they follow different rules, and knowing the rules is how a cook gets more of each on purpose.
The Maillard reaction
Named for the French chemist who described it in 1912, the Maillard reaction is what happens when amino acids, the building blocks of protein, meet reducing sugars under heat. The two combine, and their products go on reacting into brown pigments and volatile aromas, which is why a seared crust smells meaty, nutty and toasty at once.
It begins slowly at moderate temperatures and runs noticeably faster above the boiling point of water, which matters because water boils at 212°F at sea level and cannot get hotter. A wet surface, therefore, cannot brown until the water is gone. That accounts for the crowded pan of mushrooms that steams gray, the steak straight from the fridge with a damp surface, and the sheet of vegetables packed edge to edge.
It also runs faster in an alkaline environment, which is why a pinch of baking soda browns onions noticeably faster (and turns them soft, so keep it for a purée or a soup) and why pretzels are dipped in lye before baking. Dutch-process cocoa, treated with alkali, is darker than natural. Sugar on the surface speeds the reaction as well: a rub with a little sugar in it or a glaze of honey or maple browns deeper and faster, and the maple syrup guide puts this to work in its glazes.
Caramelization
Caramelization needs no protein. It is sugar alone, breaking down under heat into new compounds, from the buttery diacetyl to the nutty furans to the bitter ones that arrive if it goes too far. It starts at a higher temperature than Maillard, around 320°F (160°C) for table sugar, and the syrup darkens from clear through amber to bitter. The caramel guide covers the stages and what each is for.
Sugary vegetables such as onions, carrots and squash brown at their edges in a hot oven through both reactions at once, which is why "caramelized onions" are really Maillard and caramelization together. They take a long time because the water has to cook out first.
Which is which
| Maillard reaction | Caramelization | |
|---|---|---|
| Needs | Protein (amino acids) plus sugar | Sugar only |
| Starts in earnest at | Above the boiling point of water; slowly well below that | About 320°F (160°C) for sucrose; lower for fructose |
| Helped by | Dry surfaces, high heat, a little sugar, alkalinity, time | Dry heat, patience |
| Blocked by | Water, crowding, low heat, cold food, acidity | Water (until it boils off), too-high heat that scorches |
| Flavors | Meaty, roasted, toasted, savory, bready | Buttery, nutty, toffee, then bitter |
| Examples | Steak crust, bread crust, roasted coffee, chocolate, roasted nuts, seared fish, dulce de leche | Caramel, crème brûlée top, a reduced fruit syrup |
How to get more of it
- Dry. Pat meat and fish dry, and dry vegetables after washing. Salting ahead lets the surface dry in the refrigerator, per the salting guide.
- Hot. A properly preheated pan, an oven at 425°F for roasting rather than 350°F, a broiler for the last minute.
- Space. One layer, nothing touching, in batches if needed. Crowding makes steam, and steam makes gray.
- Fat. A film of oil conducts heat into every point of contact and carries the browned flavors. A dry pan browns unevenly.
- Sugar. A little in a rub or a glaze, or honey brushed on in the last ten minutes.
- Time. Leave the steak alone. The crust forms once it stops moving.
- Alkalinity, sparingly, as above.
Browning, done in advance
Roasted cacao is Maillard in a bar, and the roast profile is the maker's choice about how far to take it, as the bean-to-bar chocolate piece describes. Roasted nuts are Maillard on the surface, which is why a raw almond and a roasted one are different foods, per the bar nuts guide. Dulce de leche is milk proteins and lactose run through the Maillard reaction over long, slow cooking. Caramel is caramelization stopped at amber, and the caramel guide keeps the two apart. Maple syrup owes much of its color and flavor to the Maillard reaction during the long boil that concentrates the sap.
Toasted sesame oil, brown butter, coffee, malt and aged balsamic all carry browning reactions that happened before they reached the kitchen, and a spoon of any of them adds the flavor a pan would otherwise take a long time to build. Maple in a braise, a little dulce de leche in a coffee, a drop of aged balsamic on a pale sauce: each brings the taste of browning without the browning.
When browning goes wrong
Too far, and both reactions turn bitter and acrid. Burnt is the same chemistry gone past the point of pleasure, and it cannot be undone, as the guide to fixing a dish from the shelf says plainly. Too little, and food tastes of what it was rather than what it could become: a pale chicken, gray mushrooms, a soft-edged tray of vegetables.
In Denver, lower air pressure means water boils at a lower temperature and evaporates more readily, so a pan of onions can dry out sooner and a sauce can reduce before the cook expects. The altitude cooking guide has the rest.
The shop is at 263 Josephine Street in Cherry Creek, Denver, and products ship across the continental U.S. from theambrosianpantry.com. The hot dry pan is yours.
Sources & Further Reading
- Chemical & Engineering News: The Maillard Reaction Turns 100 (Sarah Everts, October 1, 2012)
- Scientific American: Food Chemists Celebrate Tasty Centennial (October 10, 2012)
- Harold McGee, On Food and Cooking (Scribner, revised 2004): browning reactions and sugar chemistry
- The Pantry Dispatch: Caramel, The Complete Guide
