The Great Wall of Rice

Today, I won’t be writing about just India. This post is about food and culture, so it’s still sticking to the main theme somewhat. It just happens to be about food and culture in a different country, inspired by a morning article in the Times of India. It also has to do with rice, which is a huge staple not only in India, but in the rest of the world.

Consider the Great Wall of China. It has been around for about 1500 years, and it doesn’t look a day older than 500. Other monuments built in that era in different parts of the world have long since been turned to dust and ash, yet the Great Wall still stands. Now, scientists from Zhejiang University in China have completed a study that explains one of the main factors contributing to the wall’s longevity. Turns out, it’s food. Rice, to be exact.

(Warning: Nerdy scientific explanation about food that you’ll never really need to know alert!)

There are three main kinds of rice: short, medium and long grain. In addition to describing the shape of rice relative to other grains, the distinctions also describe the presence and ratio of the two main starches that make up a grain of rice. These are amylose and amylopectin, which do different jobs. Amylose is a relatively short, simple molecule that can cause gelling, but is soluble in liquid. Amylopectin is long and highly branched, does not dissolve in liquids, and makes grains of rice stick to each other and liquids to gel more efficiently than amylose.

Long-grain rice, like basmati nd jasmine, contains much more amylose than amylopectin, and when cooked, the amylose available dissolves into the cooking liquid and is drained off. Also, amylose has chemical properties that keep too much water from soaking into the rice and causing the little amylopectin available to stay inside the grains. This causes the rice to separate; individual grains don’t stick together. Long-grain rice is good for making rice as a side dish to soak up a gravy or sauce. It’s the number one kind of rice used in this area of India.

Short-grain rice, like Arborio, contains a lot of amylopectin and very little amylose. Since the amylopectin is not water-soluble, it remains in the solution and causes liquids to gel up and become very sticky. This kind of rice is used to make paella or risotto, dishes where the rice is cooked in a flavorful liquid to create a sticky, creamy and delicious broth.

Medium grain rice contains roughly equal proportions of amylose and amylopectin, and thus has roughly equal characteristics of short- and long-grain rice. It’s sticky when cooked, but not as much as short-grain rice, and it holds its structure in a dish, but not as much as long-grain rice. This kind of rice is commonly used in sushi or rice soup.

What does all of that have to do with the Great Wall? Turns out that sticky rice soup made from short- to medium-grain rice grown in China was used in the mortar to piece together the wall. This isn’t exactly new information, as historians and archaeologists have known this for years. However, Zhejiang’s recent study has determined why exactly rice was important in the mortar. The amylopectin in the soup helped make the mortar nice and thick, the same way a good risotto dish is thick and creamy. This soup was then mixed with limestone to form the mortar for the bricks. Amylopectin and calcium carbonate from the limestone formed a unique, strong inorganic-organic compounded that was much better than other mortar materials of the day.

Again, this probably isn’t new information, but it was also recently discovered that amylopectin also seems to inhibit the natural crystallization of lime. In normal mortar, the inorganic compound (basically some sort of rock) continues to crystallize and change over hundreds of years, weakening the structure of the building in which it is used. Instead of the mortar eventually forming a big, messy, unstable chunk of calcium carbonate crystal after 1500 years, the microstructure that was originally created held up against weathering and further crystal growth. It’s a much more efficient and long-lasting way to build something, and rice (specifically the amylopectin in rice starches) makes it possible.

Moral of the story: rice is a culturally important food for nearly the whole worlds, so much so that it has several functions outside of its nutritional value. Oh and if you eat rice and limestone every day, you’ll live for 1500 years.

Wait, that’s not right. Kids, don't eat rocks. Unless it's salt, which is technically a rock. But that's another post.