How is one of the favorite snacks in the world formed? THE popcorn They are nothing but cereals, precisely corn seeds. The seeds inside them contain starch and water. Raising the temperature (above 100 ° C) and the pressurewater in the seed turns into steam. The water molecules, agitated by the heat, hit the internal walls of the shell, causing a growing tension which, in the end, leads to the seed breaking when the pressure reaches about 9.8 atm. From the crack comes out thestarch Which solidifies and creates the classic white cloud of the pop-corn that we know well. It will be surprised to know that the typical “pop“They do when they burst, in reality it is not caused by the outbreak in itself, but by a pressure drop within the shell of the seed which becomes a sort of resonance case. To enjoy this snack in the best way, however, there are corn qualities, in particular the Evertywho burst better than others and who will guarantee you a perfect popcorn!
The outbreak of a pop-corn is linked to its structure
Inside a seed there is a kind of starter pack with all the ingredients necessary to potentially give birth to a seedling. A chicco of corn it consists of 3 parts:
- Pericarp: the external hard shell that covers everything;
- Germ: the seed embryo;
- Endosperm: contains water and starch that constitute the initial nourishment for the future seedling.
When a corn grain reaches the temperature of boiling water (100 ° C), the water contained inside passes from the liquid state to the gaseous one, becoming steam. The more the temperature increases, the more the water molecules move quickly; in doing so They hit the internal walls of the shell solid in an increasingly frenetic way.
If the temperature increases, the pressure also increases. The seed shell (Pericarpo) manages to resist until the water steam reaches a pressure of about 9.8 ATMafter which he just can’t take it anymore and explodes. We are about 180 ° C.
Meanwhile, the pressurized and hot steam has already started to transform the starch contained in one in one Gelatinosa. When the first crack on the shell is formed, the steam and the gelified starch come out outside. The starch expands and almost instantly solidifies and cools. In this way it becomes the white cloud that we know.
The pop-corn jump
In 2015 two French engineers investigated the dynamic of pop-corn jumpingtrying to understand the causes. A pop-Corn was arranged on a hot plate and recorded by a camera. The video has been broken down into frames, in order to obtain the exact moment in which the pop-corn begins its leap. From the frames the formation of a kind of leverage has been observed that acts as one Spring for the Chicco. This lever is formed on the support surface of the pop-corn; The protuberance is compressed on the plate and that is precisely the point on which the popcorn leverages to jump.
The jump is practicable thanks tothermal energy and elastic accumulated in the heating phase. At the appropriate time this is released in the form of kinetic energy. And so the popcorn manages to perform a trajectory that we can simplify as a kind of somersault.
Because corn beans make “pop” when they explode
The two French engineers also investigated this. And no, the typical pop-corn “pop” is not caused by fracture in the corn bean.
With the recording of the synchronized sound with the video shooting frames, it has been discovered that pop does not take place at the time of the fracture, because the grain begins to release starch but you still do not hear any noise. The outbreak takes place After the fracture but before jumpingtherefore there are no correlations neither with fractures nor with the movement of the grain.
For this reason, the most accredited hypothesis has to do with the resonanceacoustic phenomenon in which sound waves are amplified. When the shell breaks, the steam contained inside it splashes out very quickly and one is generated inside the grain pressure fall. Steam excites the internal cavities of the shell that behaves like a acoustic resonator. An effect similar to what happens when we remove the cap for a bottle of sparkling wine.
Because not all popcorn break down: the corn that does not explode
The type of corn that becomes pop-corn is called Everty And it is the only cereal of the Mais family that explodes so well. If we were less demanding we could accept the pop-corn that come from Mais Flint or from the dentated corn, two types that can produce bows, even if not as well as the Eperma.
In fact, to explode at the right time, the type of corn is also selected and carefully selected. The beans are collected in autumn, when the water content in the seed is more or less of the right quantity, between 16-20%. The seeds are kept in special containers where they are dried and brought to the precise level of humidity required: 14%.
Only in this way do seeds have the proportions of right nutrients to explode at the right time. This also explains why some beans do not explode: because the amount of waterfall Inside it is too little. If the humidity content drops below 14%, the number of grains that burst and their size will be lower than the average.
