Rice crackers and starch: where the crunch comes from

The crunch of a rice cracker is a story about starch and water. Rice starch is cooked until it gelatinises, the dough is dried to a narrow band of moisture, and the pellet then meets high heat so that the remaining water turns to steam and pushes the structure outwards. As it cools, that structure sets hard and brittle. We have written before about the process from grain to cracker. This piece stops at one point and asks what happens inside the starch to make the sound.

Starch, in plain words

Starch is how a plant stores sugar. In a grain of rice it sits in tiny granules packed tightly together. Two kinds of molecule make it up: amylose, a straight chain, and amylopectin, a branched one. The ratio between them decides a great deal. Glutinous rice is almost all amylopectin, which is why it is sticky and soft. Ordinary rice has more amylose, so it cooks up separate and firms as it cools.

For a cracker, that ratio sets how much the pellet expands and what kind of crunch you get. More amylopectin means big, open, light expansion that melts away as you chew. More amylose means less expansion and a harder, denser bite. There is no correct ratio for every cracker. There is a correct ratio for the crunch a brand wants.

Gelatinisation, the step you cannot skip

Gelatinisation is what happens when starch granules meet water and heat. They take up water, swell, lose their packed structure and let the molecules move more freely. Cooked rice is gelatinised rice. On a cracker line this is the cooking or steaming before shaping.

It cannot be skipped because raw starch cannot hold steam. It does not puff. It scorches. Gelatinised starch forms a stretchy mass, something like a net, that can trap steam bubbles and inflate from the inside. The degree matters too. Undercooked, the dough keeps raw cores and puffs unevenly. Overcooked, it goes slack, is hard to shape and takes longer to dry.

Drying and puffing: water works twice

After shaping, the pellets are dried. The aim is not to dry them completely. The aim is to bring moisture into a narrow window: low enough for the pellet to be firm and keep well, high enough to leave water for the puff. This is where many faults are born, because moisture before puffing decides almost everything:

• Too wet: the cracker inflates large but with thin walls, breaks easily, or stays chewy inside.
• Too dry: not enough steam to push, so the cracker barely expands and bites like stone.
• Just right: even expansion, thin but firm cell walls, and a clean snap.

Puffing is the moment the pellet meets sudden heat, by baking, hot pressing or hot air. The water inside flashes to steam, expands many times over and pushes the starch net outwards. At the same time the heat dries and stiffens the net, locking the inflated shape in place. Once cool, the starch sits in what food scientists call the glassy state: rigid and brittle. The crunch you hear is those cell walls breaking.

Why a crunchy cracker goes limp

An open foam has a huge surface exposed to air. Starch loves water, so it draws moisture in from the air around it. As moisture rises inside the cracker, the cell walls soften and shift from glassy to rubbery. The cracker no longer snaps. It bends. That is a stale cracker.

Nothing makes starch stop wanting water. The only answer is to keep water away from it: a moisture barrier film, a tight seal, and an eater who closes the pack. In a hot, humid climate like Vietnam's, the gap between crunchy and limp is measured in hours once a bag is left open.

Two coded samples on one plate

Our partner facilities once sent the Color of Vietnam office two Let's PLAY rice cracker samples with the same seasoning, the same mould and different codes. One was light and open and snapped at a touch. The other was crunchy too, but hard, with a bite that took effort and thick fragments. On flavour they were nearly identical. The question we sent back was not about seasoning. We asked for the pellet moisture before puffing for each code.

The answer showed that the hard sample came from a drier pellet. Since then, when we order cracker samples, we describe the kind of crunch we want and ask the facility to note pellet moisture on the sample sheet. One small number has saved us several rounds of tasting.

If you work in R&D, understanding starch helps you ask the right question when a sample disappoints: ask about gelatinisation and moisture before you ask about seasoning. If you are a buyer, it explains why we ask so much about your shipping chain and storage, because crunch is kept by packaging and by how goods are stored. Anyone who would like to sit beside that plate of two samples can find the Fresher Product R&D (FMCG) role in Hanoi on our Careers page, and partners who want cracker samples and a specification sheet are welcome to contact us.