Caramel is used in many recipes. It is prepared by heating the sugar and sugar becomes syrupy and turns brown and a mouth watering aroma is released. Most people think that during heating the sugar, it melts and goes into a liquid state. But this is not true. There is chemistry behind this although no reactions really take place but there are phase changes. So physical chemistry is behind all this process.
Melting point of a substance is defined as that temperature at which the solid begins turning liquid. For pure substances consisting of single compounds this temperature is well defined and constant at atmospheric pressure. The one condition for the melting point definition is that the substance should not not breakdown during the melting. If there are impurities in the form of other substances and contaminants the melting point is not sharp and there is a range in which the whole process of melting takes place.
When sugar is heated to 160 degree centigrade, it turns into a colorless molten mass. In fact, the literature gives different melting points for the sugar. What happens is that during heating to 160 degree centigrade and further heat is supplied, temperature does not remain constant as should be the case. Near this temperature the sugar molecules also begin to disintegrate and some lower molecular weight compounds are formed. On further heating by 10 to 20 degrees, caramalization begins and it starts to turn brown emitting a mouth watering aroma.
It has also been proved that caramelization is a function of both time and temperature as many other chemical reactions are. For example, the theory for conversion of deposited organic matter to the hydrocarbons is a function of time and temperature. The effect of time is linear and that of temperature is exponential. This is known as famous Arrhenius equation. In simple words, the temperature increase is ten times more effective than time passage.
So when the sugar temperature is raised above 160 degrees, depending on the time and temperature control, different colored crystals can be obtained. and thus can be achieved to different colors by adjusting the temperature and time of heating. Following are the results from “curious cook” website.