Science of Sugar, Alchemy of Caramel

Many people consider caramel a tricky temptress. She seduces, beguiles and yes, burns! She is the product of a volatile love affair between sugar and heat. I know, you are thinking this is all a bit melodramatic. However, turning ordinary sugar into the complex and miraculous concoction caramel IS dramatic....and delicious. So let us begin at the beginning.

Plain Ol' Plain Ol'
The white stuff we know and love as sugar is sucrose. Sucrose is pure, crystallized pleasure and we are hard-wired to love the basic sweetness of it. It is also important to know that sucrose is really two simpler sugars stuck together: fructose and glucose.

A Caramel By Any Other Name
In order to talk about the alchemy of turning simple sucrose into caramel, we must first separate the notion of caramel, a stage in sugar cookery, from caramel, often thought of as a sauce, and caramels, the confection. To paraphrase Harold McGhee, "Caramelization is the name given to the chemical reactions that occur when any sugar is heated to the point that its molecules begin to break apart. This destruction triggers a remarkable cascade of events....generating hundreds of new and different flavor, color, and aromatic compounds." To add to the confusion, many people toss around the words Maillard Reaction and caramelization interchangeably. In this case, this is not the case. True caramelization of just sugar occurs without the presence of amino acids and proteins that define Maillard. So, if you cook sugar to caramel without any butter or cream, you are undergoing caramelization not Maillard.

Color Equals Flavor
Caramel is a stage in sugar cookery and it is the last stop in the line. You pass through all the other stages before you see the tell-tale signs of caramelization - color! The transformation has begun. At the early stages of caramel, the color is light and the flavor is sweeter and less dynamic. As it continues to cook, the color gets darker, the depth of flavor increases and the bitterness intensifies. Don't be afraid, come to the dark side!

The caramel stage of sugary cookery can be achieved using two distinct methods - the dry method and the wet method. The dry method consists of heating a single layer of sugar in a screamin' hot pan until it liquefies and turns the desired shade of caramel. It is fast, great when working with small amounts and I almost never use it.

Caramelization via the wet method is more time consuming and  can be fraught with peril. It seems as though everything is coming along swimmingly. Then, as you watch in horror, your boiling sugar solution turns to a solid mass in mere moments. Crystallization strikes again! What is crystallization you ask? We must digress yet again....

It's a Bird. It's a Plane. No, It's a Supersaturated Solution!
If you add just a little bit of sugar to water, the sugar crystals dissolve and goes into solution easily. If you brought this mixture to a boil, it would be close to the boiling temperature of water (212 at sea level). Nothing so exciting. Now, instead imagine a pot with so much sugar that it can no longer dissolve into the water. This solution is said to be saturated. The good news for us caramel seekers is that the saturation point of sugar to water is different at different temperatures; the higher the temperature, the more sugar can be held in solution. As this mixture continues to cook, more water evaporates out of the pot and the temperature climbs even higher. This solution is said to be supersaturated and is a very unstable state. Enter crystallization. The sugar molecules will begin to fall out of solution and crystallize back into a solid at the least provocation. While crystallization is annoying when trying to make caramel, it is not necessarily a bad thing in other candy making. Still, it is important to know how to avoid it. So... 

Chaperone At The Dance
I liken sugar molecules to hormonal teenagers at an overcrowded dance. They are singularly focused on hooking up with other like-minded teenagers. And because they are all crowded together, they keep bumping into one another. Of course it is only a matter of time. In order to prevent this from happening, you need a chaperone, also known as an invert sugar, to get in the way. Large crystals of sucrose have a harder time forming when molecules of fructose and glucose are around. So one way to prevent crystallization is to make sure that there are other types of sugar in the pot; simply add a little corn syrup. You can also simply "invert" the sucrose by adding an a little acid to the recipe. Acids such as lemon juice cause sucrose to break up (or invert) into its two simpler components.  Finally, in some instances, fats serve a similar purpose. Fatty ingredients such as butter help interfere with crystallization - again, by getting in the way of the sucrose molecules that are trying to lock together into crystals.