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Chemical Properties of Tea

Worldwide, people begin their day with some form of caffeine infused substance.

Tea has its origins as a medicinal drink and from tea ceremonies centuries ago in Asia. However, tea is now one of the most popular beverages drunk in the world, second only to water[1], thanks to its introduction to Europe in the 16th Century by the Portuguese.

Tea only really took root in England when a Portuguese noble lady married into the English royalty and brought with her, her tea drinking habit. The English populace soon following suit, as royal watchers do, but added sugar to their cup[2].

Tea’s popularity can be attributed to its psycho-active, stimulatory effects from the chemical caffeine to wake us up and keep us going through the day. Coffee is also well known to contain caffeine (the so called ‘Devil’s Cup’ as the clergy termed it) when it became popular in 15th century Europe. Coffee replaced the mind-numbing effects of constant beer drinking because the water was so polluted, and beer was sterilised and did not cause dysentery or transmit harmful bacteria. In fact, the average person drank 2 litres of beer each day, even with their cereal! Heineken and cornflakes anyone?

The reason that it was so out of favour with the church was because it had the effect of allowing people to begin to think and challenge their life situation, which happened to be heavily influenced by the organised religion of the time. To read more about the origins of coffee, ‘The Devil’s Cup’, is a fascinating story[3].

But back to tea … Tea is essentially an aromatic beverage produced by pouring boiling water over dried tea leaves (or in the case of Matcha, mixed with powdered tea leaves). Tea can have various flavours and tastes depending on brew time and type of leaf. There are sweet, nutty, floral and grassy overtones. Green, Black, Yellow, White and Oolong tea all come from the same plant, Camellia Sinensis; they are just processed or oxidised (exposure to air) differently to achieve the colour. Black tea has undergone more oxidation than green tea due to the crushing, cutting and drying process of the leaf during production, which causes the leaf cell’s active agents to be more exposed to air and turn brown. Some sources refer to fermentation of black tea, but this may be a misnomer for the oxidation process. Fermentation requires microbial activity of decomposing the tea leaf and this takes a long time. The only tea that is fermented is Pu'reh[4].

Tea can be drunk cold as well, think of iced tea in a typical backyard on a hot American summer’s day, heavily sweetened of course and served with a slice of lemon. There are many herbal teas that mix various flavours such as dried berries, thistle, and other plants, some just for fruity taste and others for the natural benefits like Camomile for calming. Herbal teas will be discussed in a separate article. Different teas also come from China, India or Japan, the latter including matcha, sencha, and bancha (the most common Japanese tea being sencha).

Green and black teas are loaded with antioxidants like catechins and phytonutrients that support overall health, in addition to the psycho-active aspects. The plant has been touted as possessing anti-cancer, anti-diabetes and cardioprotective effects. The high antioxidant content may reduce oxidative stress, improve glucose metabolism, and reduce blood lipids[5]. In short, it is healthy in moderation.

Interesting fact time. The caffeine in a tea leaf is a natural insecticide, killing pests that ingest it but also strengthening the memory of certain bugs that pollinate the plant so that they return to that plant to pollinate it again[6].

How much caffeine is too much? Both black and green teas contain less caffeine than coffee. Some cups of coffee in popular coffee shop franchises can offer more than the recommended 400 milligrams[7] of caffeine that people should consume in a day in one oversized serving. However, most cappuccinos and lattes are served with a double shot of caffeine, that is two amounts of 35 milligrams of caffeine. Furthermore, caffeinated soft drinks popular with youth offer huge caffeine content as well as harmful levels of sugar causing inflammation in the body, interfering with healthy body processes, and causing weight gain - a contributor to the obesity epidemic as well as tooth decay.

One way to remember caffeine amounts is that a normal 250 millilitre cup of black tea contains one third the amount of caffeine that an equivalent cup of coffee contains. It was widely thought that green tea had less caffeine than black tea but that has been disproven. They contain roughly the same. That is 25 to 29 milligrams for green tea versus 25-48 milligrams for black tea (a larger range). In comparison, coffee contains 95 – 165 milligrams per cup. Decaf coffee contains the same amount of caffeine as decaf black tea being 5 milligrams. Instant coffee provides about 63 milligrams of caffeine per cup[8]. The caffeine also acts in a different way when imbibed as coffee versus tea (more on that below).

As an aside, the first form of decaffeination was stumbled on by accident in 1903 when a load of coffee beans was swamped by seawater and the caffeine leached out. Later processes (and those still used today) use green beans instead of the roasted bean. The green beans are bathed in a solvent (FDA approved) that draws out the caffeine. There is also the ‘Swiss Water Method’ that soaks the beans in water, which is also chemically a solvent. The flavour and caffeine rich liquid is then strained through activated charcoal that removes the caffeine. The other method also soaks the beans in water firstly, then has them placed in a sealed stainless-steel container and blasted with high pressure carbon dioxide. The caffeine binds with the CO2 and is extracted into another receptacle. These processes can be expensive[9].

Remember the recommended amount of caffeine that we should consume each day? 400 milligrams, that is 4-5 cups of coffee per day, and it is recommended not to drink caffeine after 2pm or it can affect your natural biorhythms preparing you for sleep[10].

That being said, there is a gene that produces the enzyme that breaks down caffeine once it is absorbed into the bloodstream via the intestine. If you inherit the ‘fast’ variant of the CYP1A2 gene you metabolise caffeine quicker, those with the ‘slow’ variant can be affected by caffeine for as much as four times as long as those possessing the ‘fast’ gene[11]. Having the ‘fast’ gene could be a blessing if you enjoy lots hot brews or a curse if you are a student cramming for an exam or trying to finish an assignment late at night and need to stave off sleepiness.

Some people enjoy the taste and associated coffee culture at a café as part of their daily lifestyle. We even have tertiary education courses for learning how to make a good cup of coffee and give them a fancy name, ‘barista’ that comes from the Italian word for bartender12 who adroitly operate a steaming, gurgling, farting and frothing machine, complete with twists and loud tapping, fancy toppings, and milky patterns on top. The aroma of a coffee shop is a small blessing to those seeking to satiate their coffee craving. However, you can suffer withdrawal headaches from caffeine as it is a drug10, which keeps the industry humming. It seems that we humans can make a ritual (or profession) out of anything.

Caffeine in coffee is processed differently in the body when compared to tea. In coffee the caffeine molecules are unbound and easily absorbed into the blood stream. Therefore, too much caffeine from coffee can cause pulmonary issues or a racing heart. Whereas the caffeine in tea is bonded to tannins (or antioxidants) that need to be broken apart by our digestive system and as a result there is a longer more even absorption of the caffeine into the nervous system and cardiovascular system. Tea more gently stimulates the body and mind, and coffee excites it[7].

Caffeine, like alcohol, is also a known diuretic in high consumption; that is, it can cause the body to excrete water through urination. Water is obviously the fluid in which most of the body’s systems use and the human body is approximately 60% water (the brain is 80%). So, for healthy body functioning, it is a good idea to keep drinking water if you are a big coffee or tea drinker (more than 6 cups a day). However, the article below belies the notion that tea drinking has a diuretic effect based on several studies including one at high altitude on Mt Everest where dehydration is a concern for climbers. The finding was that there was no diuretic effect[13], but the tea drinkers had a better mood!

But wait, there is more that tea can offer. Tea contains the amino acid L-theanine which gives tea flavour but also supplies the body with the amino acid necessary to eventually produce GABA in the brain that has a calmative effect on brain activity[14]. Research has found that L-theanine can provide improved cognitive function, alleviation of psychological stress, maintenance of normal sleep, or reduction of menstrual discomfort. Further longitudinal research is still required and the combination of caffeine as when drinking tea can also be a factor of enhancing its effect than taking L-theanine alone. Supplements are sold in tablet form for stress relief that contain 400 milligrams. The amount of L-theanine in an average tea bag is 20 milligrams.

Considering how best to prepare tea can lead you down a ‘rabbit hole’, believe me. I even followed one down to discover the accidental invention of the tea bag. The tea bag was patented in 1903 and was meant to be a cute way for customers to sample a New York tea merchant Thomas Sullivan’s tea. His tea came in a small, silk muslin bag with draw string. Easy to ship and less messy to handle. Some customers simply poured hot water over the bag instead of opening the little bag and placing the tea leaves in a strainer. It caught on and with the demand the bags were changed to cotton muslin as the silk was too fine a mesh for infusion of the tea. There have been many more changes like cotton replaced with paper and strings with labels attached. More recently a plasticized pyramidal bag has entered the market to allow the tea leaf (or herbs for herbal tea) to expand and release more flavour. Joseph Tetley launched the tea bags in England in the 1950’s with success as a another labour saving gimmick. Possible war-time shortages of materials or English preferential resistance to their time-honoured process slowed its adoption before then[15].

But back to tea preparation …. There are various scientific studies and traditional practices detailing and specifying the ideal method, but as with many things, it comes down to individual taste and preference. Suffice to say, you may want to keep the following in mind.

When adding water to tea, the compounds in the tea leaf leach into the water by a process called osmotic diffusion[16]. This means the leaf structure acts as a filter between two liquids, that of the water and the water in the leaf itself. When the compound concentration in the two bodies of water reach equilibrium, then no more compounds are diffused. Therefore, there comes a point when you will have gotten the most flavour and compounds out of that brew. This said, you can reuse tea and extract its remaining beneficial compounds between 2-3 more times[17].

So, leaving a tea bag in your cup while you drink it will intensify the flavour and darken the colour of your tea as the bitter tasting dark coloured tannins are the last compounds to be released. The bitterness is partly offset by the L-Theanine[16]. However, one study showed that the released caffeine can bind with one type of the tannins called thearubigins[22], rendering the caffeine inert to the body[18], thereby making you a stronger, bitter tasting brew, but with less caffeine active for the ‘pick me up’ effect. Adding milk to the stronger brewed tea will offset the bitterness of the tannins as well. Those that ‘dunk’ their tea bag for only a minute will get the aroma of the tea and some colour but little caffeine and antioxidants.

The Lipton Tea taster that I watched on a television interview used a specifically timed process when taste testing batches of their black tea for consistency. The tea bag or tea leaves are infused with boiling water for precisely three minutes then removed. The first minute releases the flavour (aromatic flavonoids called catechins, caffeine and other phytochemicals), the second provides the colour (tannins) and the third to realise as many of the antioxidants, and at least a total amount of half of the caffeine in the leaf. Scientifically, this makes sense as each compound responsible for the attributes listed diffuse based on their specific gravity (or size or weight), the lighter aromatics (catechins) first, then caffeine and micronutrients, then polyphenols (tannins) and other antioxidants last[16].

The water temperature is key when choosing a cup of black or green tea. For black tea, boiling water (i.e., 100 degrees Celsius) is required as the leaf is already partly oxidised, whereas 80 degrees is best for green tea to help draw out the active compounds and a longer steeping time of 3-5 mins[7].

As I said, it comes down to preference and taste but once given the facts, you may want to adjust your tea taking behaviours.

Article Sources:

15. Challoner, J, Cassell Illustrated, London, 2009, p, 530.

19. Uhl, Joseph Wesley. (2016) The Art and Craft of Tea, Massachusetts. Print

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