Sunday, September 1, 2013

Green tea: won't cause you to lose weight or prevent cancer, but tastes good!







Species name: Camelia sinensis

Common name: tea plant, tea tree (see below for why you should never call this plant a tea tree), tea shrub

Location: teaching lab at Western

For the last "Plants as a Human Resource plant profile," I figured I would do one of my favourite plants in the world, and one that I exploit multiple times per day: the tea plant. The tea plant (often referred to by it's Latin genus, "Camelia") is native to China, as are all plants with the species epithet "sinensis" (it means "from China"). There are two major varieties of tea plants: one that was domesticated in India and the Middle East called Assam tea (C. sinensis var. assammica), and the other that was domesticated in China and known as Chinese tea (C. sinensis var. sinensis). There are two other recognized varieties but these are only used locally for tea, not shipped to international markets. If the tea you buy is just referred to as "tea," you can be almost guaranteed that it refers to Chinese tea, as Assam tea is almost always specified on the label. It does have a slightly different taste, and when the leaves are cured it brings out the difference in flavour. It would be appropriate to note here why I say above that the term "tea tree" should probably not be used to refer to this plant, despite the fact that it can reach "tree height." When you call something a tea tree, most people think of an essential oil that is referred to as tea tree oil, used in cosmetics and in fragrances (sometimes now used medicinally in herbal medicine, too). This is NOT the same species, and this extract is from the leaves of the tea tree plant, or Melaleuca alternifolia. Please don't drink tea tree oil...your digestive system will hate you for it.

One thing that catches many people off-guard is that ALL types of tea (black, white, green, yellow, oolong, and pu'erh) come from this plant. The way that the leaves are treated after picking is what determines what type of tea the leaves will become. There are also differences in when the leaves are picked, and how many are used in the making of different types of tea.

Black tea: leaves are picked and then allowed to fully oxidize. The leaves are fully oxidized when they turn black and start to roll inwards. The leaves may then be dried and packaged (being cut before or after drying, or left whole), or they may be flavoured before drying. Earl Grey tea has bergamot flavouring added before drying (bergamot oil is extracted from the skin of the bergamot orange), English breakfast tea is made up of plain black tea leaves, Irish breakfast is a blend of Chinese and Assam tea leaves, and Masala chai is a blend of black tea leaves and other spices (and often sugar).

Green tea: the newest leaves are picked, rolled, and immediately dried with minimal oxidization. This allows for a much milder taste, and a taste that blends well with other flavours for tea blends (like dried fruit pieces or other mild flavourings like flower petals). The quality of the leaves, the amount of time they are given to develop on the plant, and the environmental conditions the plant was subjected to during growth all play major roles in the flavour of the tea. Lower-quality teas have a much more bitter after-taste to them than higher-quality teas, and if you compare a good quality green tea to a poorer quality green tea in a taste test you'll be able to tell the difference right away. Because of the lack of oxidization of the leaves, this leaves all of the chemicals intact that many claim have health effects (more on that later).

Matcha tea: this is just a specific cultivar of tea plant where the leaves are dried without oxidization and then ground into a powder. This powder is whisked into warm water until a frothy-like consistency is reached, and then consumed. Many proponents of green tea having positive health effects say that matcha has a much larger effect on health because the leaves themselves are also consumed (unlike drinking traditional green tea).

White tea: this is a special type of green tea, where the leaves are allowed to wither on the plant before they are picked and dried. This prevents the oxidization process, but the leaves are "bleached" on the plant so they are nearly white in colour. This is emphasized by the fact that the leaves are very young and still have a dense covering of white hairs, which make the leaves look even lighter in colour. The term "white tea" does not refer to the colour of the beverage, just like "green tea" doesn't refer to a beverage that is green. If you get a cup of white tea that looks like water...you've just been served water. If you get a cup of green tea that is green (and it's not matcha, which is bright green in colour), you've been served a cup of bad quality green tea and green food colouring.

Yellow tea: this is a relatively uncommon type of tea, where the leaves are allowed essentially to rot slightly while being dried very slowly. This gives the leaves a yellow-ish appearance, and gives a very different flavour to the tea. I have yet to try yellow tea (or see it for sale in many places) myself. Sometimes the term "yellow tea" is used to refer to tea that is either green tea or white tea that is served in the Imperial court (just to make things more complicated).

Oolong tea: this type of tea is almost an intermediate between white tea and black tea. The leaves on the tea plant are allowed to wither during extreme sun exposure during the hottest months of the year, then picked and fermented (not fully fermented like black tea, but fermented enough to give a smoky and full-bodied flavour). The amount of fermentation depends on the quality of the leaves picked, and in some areas in China only one specific cultivar is used to make oolong teas. The withering of the leaves causes them to curl and twist, so watching oolong absorb water during steeping is often a sight to be seen. What looks like tiny little fragments of tea leaves actually unfurl into complete leaves. It's like magic!

Pu'erh tea: this is a type of tea produced exclusively in Yunnan Province in China, and it is made by fermenting and oxidizing the leaves of the tea plant after drying. This gives the leaves a very unique flavour which is difficult to describe, but also allows for customized fermentation and oxidation prior to shipping. The leaves are, more often than not, packaged in "cakes" to be sold and wrapped in decorative foil. This actually allows for the continuous oxidation and fermentation of the leaves during shipping and storage, which is referred to as "aging" the tea. Sometimes tea cakes are shipped immediately and may be aged by the purchaser or used right away (the flavour, and colour of the steeped tea, differs drastically depending on amount of time left to age). Other times tea cakes are allowed to age at the factory, then shipped. These are usually consumed immediately, and are very expensive to buy. The cakes are packaged with "tickets," that are always stamped with a four-digit number. The first two of these numbers represent the year in which the recipe for that specific type of pu'erh cake was developed, the third number refers to the grade of the leaves used (the smaller the better), and the last digit refers to the specific factory in which it was made. To use the leaves, they are often just chipped off the cake until the desired amount is separated, but sometimes the entire cake may be steamed to loosen all of the leaves (and then they would be stored in an airtight container after re-drying). Often a pu'erh knife is used to loosen shavings of leaves from the outer surface; you never take a "slice" of a pu'erh cake because the amount of fermentation and oxidation from the outside to the inside of the cake differs drastically. Sometimes pu'erh tea can taste "fishy" if it is fermented or oxidized too quickly, which is often a sign of poor quality. Choose your pu'erh wisely!

Onto the health effects of tea. For the most part, black tea might be a tasty beverage but it is almost entirely lacking in the polyphenols that tea is known for. If you want to drink tea to be healthy, put the Earl Grey and English breakfast back on the shelf and find yourself a good-quality green tea. There are four diseases or disorders that tea has been shown to have proven positive effects, as demonstrated in large-scale clinical trials. The first is in calming the symptoms of asthma. When green tea is consumed on a regular basis it can act as a bronchodilator, which would increase the air flow to the lungs. This does NOT mean that if you're having an asthma attack you crack out the green tea and make yourself a cup. "Green tea therapy" for asthma is used in conjunction with emergency inhalers and also the everyday inhalers; the idea is that asthma attacks will occur less often, be less severe, and everyday inhalers could be at lower doses and be used less frequently. The next three diseases all have to do with dilating the vascular system; regular consumption of green tea has been shown to help decrease the severity of angina, peripheral vascular disease, and coronary heart disease by increasing the diameter of the blood vessels, allowing for better blood circulation. This definitely won't cure any of the above diseases or prevent you from getting them, but if you are at high risk of developing any of them then it may help prolong the onset (or decrease the severity of the symptoms). That being said, the number one and number two risk factors for all three of those disease are no longer related to inheritance from your parents; they're now obesity and smoking. So do yourself a favour and quit smoking and get out and exercise!

There are a lot of other claims out there about the health benefits of drinking green tea, but so far none of them, I'll repeat that in big letters, NONE OF THEM, have been demonstrated to be true in large-scale clinical trials. People will tell you drinking green tea regularly will decrease your cholesterol and prevent the onset of cancer, neither of which have been demonstrated. Extracts from the tea leaves from the plant (the key here is from FRESH leaves. Are these chemicals still there in quantities that are useful to the body after drying and then steeping in boiling water? Unlikely) have been shown to have anti-cancer properties and the ability to reduce cholesterol but these effects have never been demonstrated in humans. There's also the strong suggestion that drinking green tea will contribute to weight loss, which I find incredibly hard to believe. Any kind of caffeine intake will "contribute" to weight loss if you don't take in more calories than you burn, because caffeine is a stimulant. Will drinking green tea specifically cause you to lose weight? No. Exercise and burning more calories than you consume causes you to lose weight. If you want to lose it, you need to put in the effort. Don't fool yourself into thinking you can drink some tea or take a pill made of green tea extracts and the pounds will melt off.

So are there any benefits to drinking green tea, other than the four mentioned above? Well, the jury's still out. There's evidence that the consumption of green tea SHOULD be beneficial, but nothing has been proven yet. That being said, there's absolutely no evidence that green tea is harmful to you, and if you're concerned about pesticide use there are now an over abundance of companies that produce organic green tea. Just don't go overboard; remember that tea does contain caffeine (although much less than coffee), and if you're drinking it to be healthy you can't be adding milk (or worse, cream!) or sugar. Learn to love the purity of the leaves :)