When moisture evaporates, transforms from a liquid into a gas , it expands. The same mass of moisture will take up a lot more volume. It will keep all the moisture in. A popcorn kernel hull is so strong that it can actually hold on to pressures up to 10 bar! This is a lot of pressure! The popcorn pops! Because of the enormous pressure build up the sudden expansion of the gas will puff up the starches within the kernel.
Once the gas has escaped the popcorn cools down quickly. As a result, the starch turns solid again and holds onto its shape. The starch undergoes very rapid cooking and gelatinization.
Not every corn will pop. You need the right variety and store it in the right way to make popcorn. Researchers have investigated the optimal properties of a corn kernel for popping and they found several important factors. First of all, the water content. The corn should contain enough moisture to reach those high pressures upon heating. However, it should not contain so much water as to soften the outer hull, which would limit the pressure it can withstand.
It is important for the corn full to remain strong and relatively dry, to withstand those high pressures. Simultaneously, you need temperatures well above the boiling point of water to actually pop the corn.
As you can imagine, the strength of the outer hull of the corn kernel is very important. The hull should be strong enough to hold onto these high pressures, however, it should not be so strong that it never breaks. Scientists found that a hull in which the molecules are structured orderly will give a better pop to the corn. As such, the type of starch is essential. Scientists describe these starches as being either hard or soft.
Half the fun of popcorn is watching it turn from a hard, little yellow seed into a white fluffy treat. Standing in the kitchen waiting for your popcorn to finish, an awesome spectacle is unfurling before you. When heated, the spirit grew angry, burst out of its home, and fled into the air as a disgruntled puff of steam.
A less charming but more scientific explanation exists for why popcorn pops. Popcorn is a whole grain. It is made up of three components : the germ, endosperm, and pericarp also known as hull. Of the 4 most common types of corn —sweet, dent, flint, and popcorn—only popcorn pops.
Popcorn differs from other types of corn in that its hull has just the right thickness to allow it to eventually burst open. Each kernel of popcorn contains a small drop of water stored inside a circle of soft starch. As the steam escapes, the temperature of the starch quickly drops and allows it to once again take solid form. The result is a perfectly fluffy, popped kernel. In every batch of popcorn, there are always a few kernels that never pop or simply crack open without popping.
There are several possible causes, but a few missing links in the popping formula are usually the cause. A faulty hull is the most common cause of a popping failure. If the hull has a small crack or otherwise compromised area, pressure will not build within the kernel. As the moisture in the kernel heats and turns to steam, it slowly leaks out of the kernel. These kernels may stay completely intact or will split open before the starch gelatinizes, causing an open but compact kernel.
Low moisture content in the kernel is also a common cause of failure to pop. Without enough steam in the kernel, pressure cannot build and the starch can not gelatinize. Popcorn manufacturers carefully dry the corn to achieve kernels with the perfect amount of moisture for optimum popping. Improper heating can also cause failure to pop. Corn pops best in dry heat produced by air or oil. This type of heat surrounds the kernel and heats it evenly and quickly. Heating the corn too slowly or at temperatures that are too low may not create enough pressure within the kernel for it to pop.
Heating the corn unevenly or too slowly may cause the hull to rupture in one spot before the entire kernel is hot enough to expand, leaving an unpopped and probably burned kernel.
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