The caramelization is a chemical reaction that involves the thermal decomposition and oxidation of sugars. Because it is usually done in closed containers or without the need to set the sugar on fire, we speak of a pyrolysis. In this the bonds are broken to release light and volatile molecules, which characterize the sweet smell of the resulting caramel.
On the other hand, as sugar breaks down, some of the new products can link together in multiple ways to give rise to a whole family of polymers called caramel, caramelenes, and caramel. These compounds are responsible for the golden and dark colors of the caramel, as well as its viscosity.
Caramelization is also defined as a non-enzymatic browning; that is, the sugars brown without the need for enzymes to intervene. This characteristic is different from the Maillard reaction, in which endless foods are browned as a result of the reaction between their reducing sugars and the amino groups of the proteins that compose them.
Although caramelization may seem simple from a culinary point of view, the truth is that from a chemical level it continues to be an arduous complex process to describe.
Caramelization, strictly speaking, only concerns sugars, for example sucrose, when heated to a high temperature. In general, this temperature is above 160 ºC; but it can vary depending on the purity of the sugar, the addition of water and its pH (acidic or basic). In other words, caramelization does not take place in the same way when dry (sugar alone) as when it is wet (sugar plus water).
At first, the sugar begins to brown and melt, pouring out of its crystals a liquid that is very reminiscent of dulce de leche or arequipe (a mixture other than caramel). The faster the heating, the darker and stickier the dough will become. That is why it is recommended to constantly beat the caramel mixed with water.
The process stops at the discretion of whoever prepares the candy. Freshly browned, it is reserved for preparing syrups or glazes; darker and viscous, on the other hand, it is used in the preparation of nougat, fondant, custards, meringues, gums and chewy sweets.
Physically, the sugar begins to brown, melt, and give off pleasant smells. Chemically, however, the description looks much more complex.
Due to the action of heat and the absence of fire, thermal energy favors all kinds of transformations, the most imminent being the dehydration of sucrose (top image) to produce a mixture of fructose and glucose.
Among the light products obtained from caramelisation we can mention ethyl acetate (fruit smell), diacetyl (butter flavor), maltol (caramelized) and furan (hazelnut flavor). Also, in the process oxygenated and unsaturated polymers known as caramel are formed, which apparently have not been deeply characterized.
All caramelisation can be considered as a set of first (decomposition) and second (condensation) order kinetic reactions. The hotter the caramel is heated, the darker and drier it will become, to a point where it begins to char (charred caramel).
Differences with the Maillard reaction
Both caramelization and the Maillard reaction are reactions from which golden or sweet products are obtained. Both are classified as non-enzymatic browning. However, the first occurs only with sugars; while the second occurs between the sugars of a food and its protein content.
Caramelisation generates caramel and other oxygenated polymers; The Maillard reaction, on the other hand, ends up producing melanoidins, which are also dark colored polymers, but which, unlike caramelans, have nitrogen atoms in their molecular structures. One is reserved for sugars and desserts, and the other for breads, cookies, cakes, meats, fish, etc.
Uses / applications of caramelisation
Caramelization, outside of cooking and baking, doesn’t have many investigative uses. That is why the uses that will be mentioned below correspond only to those of a culinary nature.
Caramelized fruits or vegetables
The caramelization reaction can be used to sweeten, in the heating process, a wide range of foods, which in turn will undergo chemical changes because their natural sugars will also react with proteins. Therefore, we have a mixture of the two non-enzymatic browning reactions (caramelization and Maillard).
For example, chopped onions can be mixed with sugar cubes and other ingredients, such as olive oil, to cook caramelized onions (top image). Similarly, apples, walnuts, bananas, tomatoes, pineapples, carrots, as well as any relatively sweet fruits or vegetables, can be caramelized.
Here it is worth mentioning that caramelized apples and glazed apples are not the same. Glazed apples or those sprinkled with a layer of milk-based caramel have not undergone chemical changes; while caramelized apples are, so their slices or pieces are more golden and sweet, without the need to sweeten them with other additives.
Brown sugar is one of the most important products that is obtained, completely or partially, from caramelization. When you start from the refined sugar, it is mixed with molasses from different sources (sorghum, sugar cane, beet, etc.), which is one of the secondary products of caramelization and the treatment of vegetable matter .
As already mentioned above, depending on the temperature and the texture of the caramel; that is, the point where caramelization stops, a great dessert menu can be prepared.
This is due to the fact that the slightly golden and soft caramel, called in many countries as syrup, is used to glaze breads, fruits, cakes, polishing their surfaces. The more viscous and darker the caramel is, the desserts will have more body and volume , such as flan (or cheese), nougat, chocolates, crowbars, among others.