Brown food is all around us, from toast to roasts, coffee, tea, and chocolate: we associate rich brown color with delicious, complex flavor. This fact is not lost upon General Foods and its friends occupying the supermarket freezer case; if there was ever a phrase wheezing from the strain of marketing fatigue, it has to be "golden brown" (followed by "zesty").
But apples also turn brown after being sliced (without any benefit to flavor), as do potatoes. Sugar, on the other hand, can become brown and delicious. Tea leaves (black tea, at least) are green when harvested, but they're brown in the tin, and certainly delicious. Browning, it turns out, is the result of at three separate processes which can also contribute to flavor.
The fortune of the French fry.
Bread, raw meat, coffee beans, potatoes, and raw cocao (to name just a few) undergo changes when heated that make them brown as well as more delicious. This process is called the Maillard reaction, named after the not-widely-known French physician and chemist, Louis Camille Maillard. In addition to figuring out some important things about how your kidneys work, Maillard also discovered that amino acids and sugars found in food react with each other (under certain conditions, as, for example, when heated to between 300 and 500 degrees Fahrenheit in your oven or dunked in hot fat) to produce a whole bunch of new components, some of them brown in color.
Fortunately, these same processes can also make foods taste better. Roast beef, maple syrup, and hash browns all benefit in both appearance and flavor. The next time you put that burger on the grill or take a sip of coffee, you can thank Maillard for figuring out why your food looks and tastes so rich. The burger alone will be throwing off about 600 separate aroma components after undergoing Mr. Maillard's reaction. While you're in an appreciative frame of mind, you may as well thank him for your that fake tan you got for your best friend's wedding...the chemicals in spray-tan react with amino acids in your dead skin cells, turning you--like your toaster waffles--golden brown (fortunately no heat is required for that particular reaction to take place).
Not so good browning...but still, nice tan!
Ever noticed how unappealing your artichoke, apple, and potato slices look after just a moment or two of sitting out on a plate? The yellow-brown color these foods quickly take on is the result of another process called enzymatic browning.
Oxygen reacts with chemicals in fruits, vegetables, tea, and even tobacco leaves, called phenols (phenols are the healthful anti-oxidants that we're hearing so much about, although I wouldn't go looking for them in tobacco) to produce new brown compounds called melanins. On apples, this oxidation doesn't help the flavor, but on tea, it does. And yes, you guessed it, melanins produced during enzymatic browning are in the same family as the melanin you learned about in high school biology class, the one your body makes more of during sun-tanning.
Fortunately, it's relatively easy to control undesirable enzymatic browning. Adding lemon juice to your apples or avocado pieces destroys the browning pre-cursors, as will depriving your food of oxygen by throwing those sliced artichokes into a bowl of water. Industrial salad bars take the same oxygen-deprivation approach by liberally sprinkling sulfites onto their shredded lettuce. If you think wine's bad, consider that salad bars have literally thousands of times more sulfites added to prevent browning.
Carmelization, no tanning involved.
This type of browning does not involve oxidation and enzymes, but it does involve sugar voo-doo, making it more akin to the Maillard reaction. Unlike the Maillard reaction, no amino acids are required to make carmelization happen. The sugar takes leave of itself, producing melanins and new flavor components, just by adding heat.