Bonds. Water. Starch. And the science of sushi’s sticky rice.
The rice grains used for sushi need to stick to one another, otherwise our meal will fall apart (literally) very quickly. Where does the sticky rice for sushi come from, and how did it get so sticky?
The rice we are most familiar with and tend to eat is white rice. White rice is parboiled and polished rice: The husk, bran, germ and aleurone layer (outer layer of the endosperm) have been removed, and only the endosperm is left.
The endosperm is starchy. Starch is insoluble in cold water, but when the water is heated, the energy causes the hydrogen bonds between the starch molecules to loosen and water penetrates the starch molecules.
The starch granules start to swell with water, and some will break down. When this happens, starch is released, forming a sticky goo. How sticky this is depends on the amount of amylose (one of the two starch molecules) in the particular types of rice grain.
Amylose reduces the ability of water to penetrate the starch, swell and break down for the release of the goo-ey stuff.
- Long grain rice, which has a higher amylose level, is fluffy and separate.
- Medium grain rice, which has a lower amount of amylose, is moist and slightly sticky.
- Short grain rice, which has the lowest amylose content, is soft and moist, and the stickiest of all.
The last is what we usually call the “sticky rice” used in making sushi.
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(photos: in order – depositphotos/valbunny; megija; PixelsAway)