Forget the stiff upper lip. Getting to know starches can dramatically reduce stress in the kitchen. There are two things that transform these molecules with dramatic effect: water, and heat. Starches go through different stages when heated variably, and this, unknown to us, gives much of our cooked food its texture.
How does it all work? It helps to think of starch as a regular guy with a routine job, particular about his appearance, not easily swayed by circumstance. That’s starch in its native state. Soak raw rice in water, for instance, and it absorbs a little of it but otherwise registers no change.
Add heat and liquid, though, and you have the equivalent of a weekend out on the town. When first warmed, starch begins to declare its affection for water, hugging it close and not letting go. The organised molecular structure of the grain begins to unravel.
This process of gelation starts at 50 to 80 degrees Celsius, depending on the grain. Oats are at the lower end of this scale, more easily swayed; rice is more reluctant, harder to unsettle.
They all eventually yield, and this is good news for humans. Without gelatinisation, grains — and all the energy they hold, entrusted to them for a future plant — would remain inaccessible. They would be hard, crunchy and inedible to humans.
After gelatinisation (Friday night, let’s say), comes pasting (Saturday evening). Sustained heat and moisture cause grains to expand to such a degree that they become like tiny starch bombs. Still, the outer layer of the endosperm — called the aleurone layer — is so strong that it often doesn’t actually give way. Stir gently, however, and the pressure becomes too much. The starches burst their bounds, and a grainy mix turns quickly into a thick, gluggy solution. That is how one gets a deliciously moist khichdi or bisi bele bhaat.
(Biryani, let it be said, does not take kindly to talk of a weekend off. This is grain that stays on the clock. Timing is everything. And so one learns exactly how much water and how many minutes of heat it will accommodate; while never worrying about such things when it’s khichdi partying hard in a cooker.)
Grind grain into a flour, add liquid and heat, and the pasting occurs almost instantly. The long starch strands act like a spider’s web, bonding with water all through, turning any solution into a gluggier mix. This is why even a little bit of flour, helps thicken a sauce.
But… heat such a mix for too long and it thins out again. Because too much heat breaks the web of starch into globs that can no longer reach out to each other and connect.
In all starchy preparations, there is a third phase that begins when the heat is turned off: the cooling stage. Think of this as a sobering-up. The gelatinised or pasty starch begins to returns to its regular self; looks around; sees what has happened to its hair and its shoes. And wants nothing more than to revert to its original, organised structure.
Having brought random water molecules home with it, it now realises it wants them out.
At this stage, starch molecules attempt to recrystallise, in a process called retrogradation. This is the reason cooked rice hardens in the refrigerator. One can slow retrogradation, with the help of proteins, fats, sugars or salts. These hold on to moisture, and can keep a dish from drying out.
Unlike most people after a wild weekend, though, the grain itself will never be the same again. Gelatinisation is irreversible. The mix can be dehydrated and some of the moisture removed. But its starches are now unlocked. Its aleurone layer is gone.
It is vulnerable and fading fast. Its shelf life has gone from potentially decades, to a few weeks at most.
One bender is sometimes all it takes, kids!
(To reach Swetha Sivakumar with questions or feedback, email upgrademyfood@gmail.com)
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