Science over breakfast

Vaishnavi Sridhar shares interesting facts as two siblings bite into a dosa

Eerulli! (Onion) I smell eerulli. Who is cutting them?” asked Abby sniffing around the house. “I am making masala dosa for breakfast,” answered Amma. The whole family looked forward to Amma’s breakfast specials. “But I don’t like eerulli. They are bad,” said Abby angrily. “Abby, why are they bad?” Iddi asked her younger brother. “They make people cry,” Abby said innocently. He had noticed that whenever anyone cut eerulli, their eyes would well up. Abby felt that anything that made someone cry was bad.

Amma, Appa, and Iddi were amused by his innocent statement. They decided to explain why cutting eerulli makes one cry. “Abby, this is how the eerulli tries to defend itself. Animals can run away, hide, or fight to save themselves. But plants cannot run away, can they? So, they use other ways to defend  themselves,” explained Iddi.

Abby thought a little about what Iddi had said. “So, it’s like pepper spray,” he said. “In a way, yes. Plants use many ways to defend themselves, such as chemical or structural defenses, among others. Thorns and spines are examples of structural defenses,” said Iddi. 

“Many living things try to get a bite of the eerulli plants. Do you remember observing a section of eerulli peel to see cells? When these cells are damaged, they release chemicals stored inside, which eventually makes us cry. So, like thorns can prick you, cutting or biting into an eerulli can make you cry,” she explained. “As they grow, onion plants take in sulphur from the soil, to make sulphur containing compounds. When eerulli cells are damaged, these compounds come in contact with an enzyme. This enzyme and the compounds are stored separately in intact cells. In damaged cells, both react to form a gaseous sulphur containing chemical. When this chemical reaches our eyes, it combines with the water in our eyes to form sulphuric acid. This causes the irritation,” she added.

Abby’s mind was blown away with all the science. Who knew that physics, chemistry and biology all came together during the production of these chemicals that made one cry! Abby understood that eerulli contains chemicals that make us cry. He wondered what happens to our eyes when the chemicals reach it. “These chemicals are sensed by the nerve cells in our eyes as irritants. The response is to produce tears to wash out the irritants and to protect our eyes,” said Iddi. “Oh, that makes sense!” said Abby.

“Yes. That is why I usually chop eerulli with the windows open or with the fan on. Putting them in cold water helps too,” said Amma. “Some scientists have developed varieties of eerulli that won’t make us cry,” said Iddi.

“Wow! Tell me more,” said Abby with his eyes wide open. “Sure. Do you know that there are chemical reactions involved in the making of a dosa?” asked Iddi. “Have you ever wondered why after grinding the dosa batter, we let it sit in a warm environment overnight? And why does the batter appear bubbly, and smells sour the next morning?” she asked.

“Dosa is a fermented food. It is made of specific ratios of soaked rice and urad dal. The batter also contains methi seeds and salt. All these are ground up with some water and left overnight at a warm temperature to ferment,” she added. “Fermentation is a kind of chemical reaction in which microbes break down sugars into other substances. This occurs in the absence of oxygen primarily and helps these microbes generate energy. There are different kinds of fermentation. In the case of curd, bacteria ferment lactose sugar found in milk into lactic acid. Scientists have found that dosa batter contains different kinds of bacteria that produce lactic acid, carbon dioxide, and small amounts of ethanol. The batter contains yeast too. The fermentation reaction results in the bubbly and sour smelling batter,” she explained.

“But where do these microbes come from?” asked Abby. “When Amma makes curd, have you noticed that she adds some curd from the previous batch into lukewarm milk? This curd is the source of the microbes. In the case of dosa, the microbes ccome either from urad dal or methi seeds. They might even come from the air or the water used to whip up the batter. Adding salt helps control the reaction and prevents harmful microbes from growing in the batter, ” said Iddi. 

“Fermentation makes it easy to digest dosa. Even though dosa is easy to digest, it is a good idea to add ginger or pepper or other digestives to help with further digestion. These can be added to the chutney, sambhar, or to the batter itself,” she added. “This is so cool. Cooking food is basically a lot of chemistry,” remarked Abby. “Absolutely. There are many scientists around the world who study and develop food products,” said Iddi. “Anyone who can master the art of cooking is an experimentalist in a way,” she added.