caramelize
Cook slowly, usually over low-to-medium heat, until natural sugars brown and develop a deeper, sweeter flavor -- classically applied to onions, but the same principle applies to other vegetables and to sugar itself.
How to do it
Two quite different procedures share the name because they share a chemistry. Caramelizing a vegetable means driving off its water first and only then browning the sugars left behind, which is why onions appear to do nothing for a long stretch and then color quickly. Caramelizing sugar on its own skips the water entirely and goes straight to the browning, which is why it takes minutes rather than the better part of an hour -- and why it is far easier to ruin. In both cases the target is a deep amber brown that smells sweet and faintly nutty; black and acrid is a different thing, and it cannot be rescued by adding anything to it.
Vegetables, onions above all
- Slice reasonably evenly, and plan for real time -- 30 to 45 minutes for a properly caramelized pan of onions. Turning the heat up does not shortcut it, it only burns the edges while the rest stays pale.
- Use the broadest pan available. Surface area is what lets the released water evaporate; a crowded or deep pan traps it and the onions stew instead of browning.
- Cook in a modest amount of fat over moderate heat with a pinch of salt. Expect a long stretch where the onions simply soften and go limp, releasing a surprising amount of liquid -- no real browning can begin until most of that has gone.
- Stir occasionally, not constantly. The onions need sustained contact with the hot pan surface to color, and constant stirring prevents exactly that.
- As browned residue builds on the pan bottom, add a tablespoon or two of water and scrape it across the surface. That dissolves the residue back into the onions and stops it scorching -- repeat as often as needed, since it is the main control available.
- Stop when the onions are deep golden-brown, jammy, much reduced in volume, and taste distinctly sweet. Pale gold and floppy is softened, not caramelized.
Sugar on its own
- Use a heavy pan, ideally with a light-colored interior. Judging caramel against dark nonstick is genuinely difficult, and color is the only signal that matters.
- Either melt the sugar dry over moderate heat, or add just enough water to wet it into a slurry first. The wet method is slower and more forgiving; the dry method is faster and colors unevenly unless the pan is kept moving.
- Once it begins to color, do not walk away. The gap between amber and burnt is a matter of seconds.
- Swirl the pan rather than stirring with a spoon, which encourages the dissolved sugar to crystallize back into grit.
- Pull it off the heat a shade lighter than the color wanted, and stop the cooking straight away -- by adding the waiting liquid, or by setting the pan's base in cold water. A pan left standing carries enough heat to take caramel past where it was pulled.
Common pitfalls
- Heat too high -- the edges burn while the rest stays pale.
- Heat too low -- browning becomes unnecessarily slow.
- Overcrowding the pan -- trapped moisture encourages steaming instead of browning.
- Adding sugar to speed things up -- it sweetens the onions but doesn't substitute for actually browning them.
- Confusing brown with burnt -- dark brown tastes complex, black tastes bitter and acrid.
Why it works
Sugars broken apart by enough heat recombine into hundreds of new compounds with new colors, aromas, and flavors -- this family of reactions is caramelization. Water gets in the way: a wet ingredient stays near water's boiling point as long as substantial free moisture remains, so strong browning only becomes easy once the surface has dried out. Caramelization is a different reaction from Maillard browning, which involves sugars reacting with amino acids rather than breaking down on their own -- onions typically involve both at once, while plain sugar caramel is caramelization alone.
Equipment
A wide, heavy-bottomed skillet or sauté pan is ideal -- the broad surface lets moisture escape and the heavy base spreads heat evenly, cutting down on hot spots. Stainless steel and well-seasoned cast iron both work well; stainless steel also makes the color of the fond easier to judge by eye. For caramelizing plain sugar, a pale or stainless pan makes the color of the caramel itself easier to track accurately than a dark pan would.