The fresh-baked bread provides that pleasant aroma as soon as the oven door is pulled down. The mouth starts salivating and watering when we smell this. It might seem like a magic trick that all cooks have up their sleeves which they have mastered to perfection, but don’t want to divulge.
As foodies, we may be asking ourselves – what is happening? We need to take a look at the chemistry and molecules involved.
Sugar and amino acids play a major role. Found on the surface of meat and bread dough, the special feature of sugars and amino acids is that they bond with each other (love at first sight), as heat (energy) plays the role of go-between and balancing their reactive attitude. Their love and bond is quite productive and hundreds of molecules are born a few minutes after they meet. Some of them are moving around, giving that fragrance and aroma in the kitchen. Some are freed while chewing and are responsible for that typical roasted taste, while the majority of them are responsible for the coloured molecules, which explains the golden crust colour, familiar grill marks and the browning.
This reaction, which applies to the taste, flavours and aroma (sensory) in cooking, is called the Maillard reaction. It was named after the French scientist Louis Camille Maillard, who conducted the research in this field during the early 20th century. This is a very complex chemical process and plays a major role in sensory evaluation.
In this process, the speed of the reaction is determined by temperature and time – it even takes place in champagne, albeit extremely slowly. The higher the temperature, faster the reaction and hence the characteristic dark coloration and development of the flavours described above.
The reaction is also more significant at alkaline pH values, therefore soda is used for pretzel dough or to make a better dulce de leche (sweetened caramelised milk that is traditionally made by reducing a mixture of milk and sugar over heat). Another factor is humidity, which is why the food must not be too moist or too dry to achieve a perfect result.
When the temperature exceeds 120 degrees Centigrade and some water is present, an undesirable Maillard reaction can also occur in baked goods or when deep-frying foods that contain a lot of carbohydrates. Among other things, this can produce the harmful substance acrylamide — a white odourless solid, soluble in water and several organic solvents). To avoid this, it is recommended not to deep-fry above 170 degrees Centigrade. This can be best explained taking the French fries as an example.
When raw fries are placed in oil (140-165 degrees) at room temperature, the heat spreads in the fries. This does not happen too quickly, because the potato is a poor conductor of heat. When the temperature of the deep-fat fryer reaches around 58 degrees, gelatinisation begins and the potato softens. The core will not exceed this temperature and therefore stays a little soft. However, the surface reaches 100 degrees quickly. The water in the fries evaporates. A light, dry crust is formed with holes that allow water to pass through. This is the basis for crispiness.
If the crust exceeds 100 degrees Centigrade, it reaches the temperature at which the Maillard reaction begins. This creates the yellow-brown colour. The oil now gets into action — it gradually oxidises and produces molecules that mix with the Maillard reaction. This produces the deep-fried aromas that have enticed us into the kitchen/cafe.
During the frying process, oil can barely penetrate the potatoes due to the pressure of the evaporating water, thus we have some oil clinging to the chips (measurement shows that it is about quarter of the net weight of a single chip). Thus to save a few calories, it is worth removing the excess oil from the fries with absorbent paper towels. For that classic preparation in a deep-fat fryer, it is best to pre-fry for 60 seconds and then finish off by deep-frying for 5 minutes.
For the road: Have you ever noticed that once you’ve eaten the fries, that deep-fried smell is no longer appetising? The level food craving depicts on how hungry we are. By the way, did you know adults like roasted flavours more than children do?
