It is time for a new blog post: this time on the tea plant Camellia sinensis. This has been a really interesting plant to research. Thank you to Stephen Welsh (Curator of Living Cultures at the Manchester Museum) for allowing me to use some pictures from his collection.
Camellia sinensis is an evergreen shrub that can reach up to 17 metres in height, but is usually trimmed to below 2 metres when cultivated to facilitate picking of leaves. More commonly known as tea, the leaves of this bush are bright green, shiny and often hairy on the underside. It takes roughly 3 years before a new plant is ready to be harvested. However, once ready to be harvested, the leaves can be picked up to 30 times per year.
Due to the wide variety of habitats available to the plant, there are many different varieties of the tea plant. Of these varieties, there are two commonly grown today: Camellia sinensis var. sinensis (Chinese tea) and Camellia sinensis var. assamica (Assam or Indian tea). Chinese tea tends to be the hardier variety that produces small, narrow leaves used for green tea and China’s black tea. In contrast, the Indian variety possesses larger, leathery leaves that often appear to sag off the branches.
History of tea drinking
The origin of the tea plant is not clear but fossil records show that it has existed for millions of years. Tea is thought to have originated in China and ‘wild’ Camellia sinensis can be found in its forests, though these may only be relics of past cultivation. Either way, the earliest record of tea consumption is in China during the 10th century BCE. Though likely to have been originally drunk for medicinal purposes, by the 4th century ACE the art of tea drinking was deeply ingrained in Chinese culture. According to documents from the Tang dynasty, by 650 ACE Camellia sinensis was being grown in almost all of the Chinese provinces. The ritual of making a drink of tea, as well as the ability to recognise type and quality, became the height of sophisticated society. Around this time, tea was introduced to Japan for the first time by travelling Buddhist priests. It quickly spread among the elite and the Japanese tea culture soon developed. By the 12th century, all social classes in Japan drank tea.
For the most part, tea drinking remained an Eastern tradition until the 16th century. Travelling Portuguese priests and merchants were introduced to tea during their travels to China. They in turn spread Camellia sinensis to Europe and the West. The drink quickly became fashionable in Britain, though it was not widely consumed through the 17th century because it remained an expensive plant to import.
Tea smuggling became big business during over the next century as all social classes in Britain began drinking tea in large quantities. It became so lucrative that, in 1785, the British Government had to abolish tax on tea to try and eliminate the smuggling trade. They even began to break Chinese monopoly on the tea market, by mass cultivating Camellia sinensis in India and other British colonies. At first they tried to grow seeds from the Chinese variety, before discovering that there was a second type endemic to India (Camellia sinensis var. assamica). Tea steadily became more affordable and soon became a permanent fixture within British culture. By the early 18th century, Britain was consuming over nine million cups of tea per year.
Tea is now the most consumed beverage in the world, with the exception of water (Britain alone uses over 3 million tonnes per year). As a general rule, tea is divided into a number of categories based on how it is processed. There are many different social rituals (such as Japanese tea ceremonies and British tea time) associated with the plant and a vast number of different styles and additions (like milk and sugar). Flavourings and seasonings, such as chamomile and mint, can also be added to tea. Over the past decade, tea has even been used to create liqueurs and other beverages, including martinis.
Harvesting Camellia sinensis is a labour intensive process but overproduction of the plant has led to falling prices and poor wages for workers. To combat this, Fair Trade tea producers charge more for their products in order to pay suppliers a higher price, therefore providing better wages for workers.
Before the culture of drinking tea arose, Camellia sinensis was used for medicinal purposes. It is believed that as far back as prehistoric times, people have used the leaves for wound healing. The first definitive use of tea medicinally was around 5,000 years ago in ancient China. Since then, Camellia sinensis has featured heavily in traditional Chinese medicine and is used as a cure for over 200 illnesses. These include for digestive problems, fevers, paralysis, nervousness, insomnia and insect bites. The most common use for tea is as a stimulant, which is due to the caffeine content.
Caffeine makes up approximately 3% of tea’s dry weight and is included in many over-the-counter medicines. It is often combined with pain relieving remedies, like aspirin, to counteract their sedative-like effects. Camellia sinensis also contains small amounts of theobromine and theophylline, which are both stimulants similar to caffeine. Theophylline is used in the treatment of a number of respiratory diseases, including asthma. Tea also possesses a number of flavonoids, which are secondary metabolites (compounds whose absence can cause long-term effects on health). These flavonoids have anti-oxidant, anti-inflammatory and antimicrobial properties.
Although not strictly an effect of Camellia sinensis, the process of making a cup of tea requires boiling water. This destroys pathogenic microorganisms, thereby preventing waterborne diseases from spreading.
Though used extensively in traditional medicines, studies into the compounds within Camellia sinensis have not conclusively shown that they have any effect against human diseases. In addition, tea does not possess any essential nutrients in a significant quantity, with the exception of manganese. Drinking tea also results in large amounts of aluminium in the human body, which has been associated with an increased risk of Alzheimer’s disease. However, there is insufficient evidence to support this and the level of aluminium in tea is still generally regarded as safe.
For the most part, the concentrations of caffeine and other compounds in tea are considered safe. However, there can be negative side-effects if consumed in large quantities. The most common problem is that caffeine can cause headaches and anxiety. It can also inhibit iron absorption in the gut and stimulate the production of urine. Many of the undesired effects of caffeine are mitigated by other compounds, particularly antioxidants, in the tea unless consumed excessively.
When ingested in high doses, Theophylline can have more toxic effects than caffeine. These include heart problems (such as heart palpitations), insomnia and convulsions. Camellia sinensis also contains small amounts of tannins (which have been linked with cancer) and oxalate (which can cause kidney stones). However, prolonged overconsumption is required for them to reach a level that is harmful.
Other uses and interesting facts
In addition to its use as a beverage and in medicine, tea leaves have also been used as an ingredient in some food recipes and in some cosmetic products. Despite being hugely popular as a drink, Camellia sinensis is actually considered a pest species in some areas of the world. There have been reports of the tea plant spreading in Madagascan forests, dampening the regeneration of the native forests that are important lemur habitats.