Tea bags: A hot cup discovered in hot water

By the time the water has changed colour, it has saturated the tea bag, and the tea particles have bounced all around the cup, and the tea is ready.
Representative image
Representative image

A blend of inventiveness, simple chemistry, and chance revolutionised the way tea is drunk on the go. While tea has been enjoyed for ages, the tea bag is a more modern concept, dating back to the early 20th century.

The earliest versions of tea bags were handmade fabric pouches or silk muslin bags used to hold tea leaves, which were stitched shut and placed directly into teapots.

The advent of the first tea bags is strangely humorous, emerging from an idea that was not intended. In 1903, Thomas Sullivan, a tea merchant from New York, intended to send samples of tea to his customers in small silk pouches. However, his patrons mistakenly thought the bags were meant to be used directly into the teapot, rather than emptying the leaves into it. They found the small pouches convenient and thus the idea of brewing tea in small bags was born. It was in the early 1900s, when Sullivan started selling tea bags commercially. The initial hand-sewn silk pouches evolved into paper bags we are familiar with today. They became highly popular, especially during World War II, when there was a shortage of loose tea.

Osmosis and diffusion

How does a tea bag do its trick? When a tea bag is dropped into a mug of hot water, the latter starts changing colour according to the tea leaves/powder inside, and in no time all of the water has changed colour without even stirring the cup, while also brimming with flavour.

All matter is made up of molecules, which are always in motion and colliding with each other. A tea bag contains numerous tiny holes, which makes it permeable. Accordingly, the hot water moves through the permeable membrane of the bag and interacts with the dry tea leaves. If there are more water molecules outside the bag, the water moves inside and makes the concentration of water molecules homogenous. This process is called osmosis.

Simultaneously, tiny particles from the tea leaves get dissolved and move throughout the cup, wherever there is a lower concentration of tea particles. This process is called diffusion. By the time the water has changed colour, it has saturated the tea bag, and the tea particles have bounced all around the cup, and the tea is ready. Tea bags can also be used in a cup of milk.

Meanwhile, tea bags, though convenient and popular, can have several harmful effects on health and environment. Researchers state that most teabags available in the market contain plastic like polypropylene. When dipped in hot water, they release billions of micro and nano plastics and harmful chemicals into the tea, potentially leading to health issues. Besides, to make the paper stronger and resistant to tearing when wet, it is treated with chemicals like epichlorohydrin.

Also, single-use teabags contribute to waste generation, while biodegradable and compostable teabags can be problematic if not disposed of properly. Production of paper for tea bags can also contribute to deforestation and the loss of habitat.

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The New Indian Express