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
For onions, slice them reasonably evenly and use a broad pan with enough surface area for moisture to escape. Cook them in a small amount of fat over moderate heat -- they'll soften and release a surprising amount of water first, and only after much of that water evaporates can real browning begin, which is why onions seem to sit there merely softening for a long stretch before they suddenly start coloring much faster. Stir occasionally rather than constantly, since the onions need sustained contact with the hot pan to color. As browned residue builds up on the pan bottom, a tablespoon or two of water added and scraped across the surface dissolves that flavorful residue back into the onions and prevents scorching. True caramelization takes real time -- turning the heat up dramatically doesn't shortcut it. For plain sugar, watch the heat even more closely, since the gap between amber caramel and burnt sugar is small.
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.