Science Buddies: "Ask an Expert"

When making candy, what make the candy become a 'soft-ball' when heated to 234 degrees Fahrenheit?

From wikipedia:

Candies are prepared by dissolving sugar in water or milk to form a syrup, and boiling it until it starts to caramelize. Depending on the solvent and the end result of the process, the product may be called candy, caramel, toffee, fudge, praline, tablet or taffy. The recipe used also predicts how hard, soft, chewy or brittle the end result should be. The eventual texture of candy depends on the temperature to which the sugar solution is boiled, since the presence of a solute in a liquid elevates the boiling point of the liquid. As the syrup is heated, it boils, which causes the sugar concentration in the syrup to increase due to evaporation of the water, which raises the boiling point even further. The relationship between the boiling point and the sugar concentration is predictable, and so heating the syrup to a particular temperature ensures a particular sugar concentration with some accuracy. In general, higher temperatures — which imply greater sugar concentrations — result in hard, brittle candies, and lower temperatures result in softer candies. These "stages" of cooking have been named and correlated with the cooking temperatures, and are frequently specified in recipes thusly:

"thread": 230-233°F / 110-111°C
"soft-ball": 234-240°F / 112-115°C
"firm-ball": 244-248°F / 118-120°C
"hard-ball": 250-266°F / 121-130°C
"soft-crack": 270-290°F / 132-143°C
"hard-crack": 295-310°F / 146-154°C
This unusual nomenclature derives from the process used to test the syrup in times before thermometers became affordable. A small spoonful of the hot syrup was dropped into a glass of cold water. The characteristics of the resulting lump of sugar could then be used to determine the concentration of the syrup. "Thread" stage produces long strings of hardened sugar, while "ball" stages result in a smooth lump with the corresponding hardness described. The "crack" stages create a ball of candy so brittle that the rapid cooling from the water literally causes it to crack. This method is still used today in some kitchens; however, a candy thermometer is much more convenient, but has the drawback of not automatically adjusting for local conditions such as altitude as the cold water test does.

Once the syrup reaches 340°F or higher, the sucrose molecules break down into many simpler sugars, creating an amber-colored substance known as caramel. This should not be confused with caramel candy, although it is the candy's main flavoring agent.

Thank you.
Do artificial sweeteners do this too? If not, why not?

Aspartame is not heat stable, although this just refers to the fact that it gets bitter when heated in this case. Acesulfame-K is heat stable, as is Saccharin and Sucralose.

They don't, to my knowledge, caramelizes when heated.

DiabetiSweet (which is a combination of Acesulfame-K and Isomalt ) does caramelizes, just like real sugar.

when I did my expirament, the sucralose (Splenda(R)) batch burned before reaching the required temperature. Since it was a controlled expirament, we could not change anything to keep this from happening. Why did this fudge burn? Why didn't the sucralose work as a crystallized fudge?