Wednesday, April 15, 2015

What defines a tea?

There are hundreds of different names for tea : Darjeeling muscatel, Bi Luo Chun, Tie Guan Yin, Hojicha,  Pu-erh, Bai Mu Dan, Tai Ping Hou Kui, Dong Ding, Dong Fang Mei Ren, Gyokuro, etc…
Just like the classification of European wines, this system requires a lot of knowledge; you have to learn about the specifications of each tea one by one.

I would like to give a simpler approach to tea. By focusing on the aspects which have the most influence on the taste of tea, you will be able to have a rough idea of what the tea will taste like just by looking at the leaves.

Early Spring 2014 Jingmai tea

First, let’s start with things that are not obvious to see: the cultivar. Apart from Pu-erh tea, most of the teas come from selected tea trees. For example, Tie Guan Yin comes from a specific cultivar, its processing is the same as many Taiwanese high mountain teas. Tea trees are mostly selected for the taste of their leaves, and to a minor extent for their capacity to resist certain disease or cope with frost.

There are two main varietals: sinensis and assamica, also called China and Assam or big and small leaf varietal. Generally speaking, var sinensis has small leaves, a low yield, a better resistance to low temperatures and more fragrant leaves than var assamica, which is a more robust varietal. Their main botanical difference is that sinensis is a shrub: it grows many small branches from the ground, assamica is a tree, it grows a single trunk and grows taller. The difference in leaf size can be confusing because there is a middle ground where leaves could come either from sinensis or assamica. There are also wild varietals such as Camellia taliensis in South East Asia or Camellia formonensis in Taiwan.

China varietal in Pandam Tea Estate, Darjeeling

Assam varietal in Pandam Tea Estate, Darjeeling
The harvest time, altitude and agricultural techniques have influence on the strength of tea because the tea leaves will make different amounts and types of chemical compounds according to the environment conditions: temperature, sunlight,  nutrient and water availability, presence of some insects…
Finally, the leaf grade has a big influence on the tea quality. More buds give lighter and more fragrant tea, while older leaves give a stronger brew with more bitterness and astringency. Tea with lots of buds is more expensive because it takes more time to pick, but it’s not necessarily the tea you’ll like most, some people, including me, prefer 1 bud/2 leaves tea over single buds or 1bud/1 leaf. A high amount of tea stalks makes tea sweeter.

A good tea starts in the field, but its quality is glorified in the factory, the large variety of taste is obtained thanks to many different processing techniques. However, those techniques have an impact on a couple of factors only, which I’m going to detail now.
The oxidation state might remind you of your worst cramming time at university, trying to understand organic chemistry. Tea has many polyphenols, which are (in)famous for having many possible oxidation states. Simply put, the more oxygen atoms attached to a molecule, the more oxidized it is (dear chemist readers, I’m sorry for taking such shortcuts!). The more oxidized a tea, the darker it is, note that most of the teas being black, green or wulong, they are solely differentiated by their oxidation state.  I’m not going to go into further details on what happens in the leaves, but oxidation state of tea can be influenced by heat treatment (pan frying or steaming) and aging (especially in Pu-erh teas and white tea).

Experimenting with oxidation

Roasting is another way to make a tea darker and enrich its flavor profile. Just like coffee, some teas are roasted, a chemical reaction occurs and the leaves get darker, this is the same process that makes meat turn dark when you cook it, it is called the Maillard reaction. Roasted tea leaves have a hard time unfolding when they are brewed, this is because the leaf cells are damaged during the process and probably stick together. It also brings out more astringency because as some cells burst, more chemical compounds will be released during the steeping.

Most of the teas are rolled, some of them so heavily that the leaves are broken during the process, just like many Darjeeling teas. During the rolling process, the cell walls are broken; just like roasting, this allows more chemical compounds to be released during the brew. Heavily rolled teas pack a punch in the first brews but struggle after a couple of infusions. They tend to be more bitter and astringent; this is what gives “briskness” to the Indian teas.

Heavily rolled tea

Finally, tea can have added flavor, wanted or not. Smokiness or off-flavors are generally considered as flaws but can be desirable traits. Mixing fragrant flowers such as jasmine is a traditional way to bring more fragrance to the tea leaves. More modern techniques involve the spraying of artificial flavors or essential oils.

To summarize, if you want to know what kind of tea you’re dealing with, try to know which cultivar it comes from, in which conditions it was grown, when it was harvested, look at how dark the leaves are, check if the leaves seem roasted, oxidated, heavily rolled or broken. And more importantly, enjoy your tea session.

Tea makers don’t see each tea categories as independent. In the field and factory, you can virtually make an infinite number of different teas because you can always do something more or less: weathering, rolling, frying, roasting, drying… These are slides, not switches. Knowing this, debating about whether Darjeeling tea is black or wulong tea then becomes irrelevant. A name is only an approximation; the real thing is what you get in the cup.  

Sunday, March 29, 2015

Organic matter

In my last post, I talked about the importance of a good soil structure for having a high fertility. Another very important factor is the percentage of organic matter present in your soil.
Organic matter is essentially made of carbon, the atom that defines life. Carbon is the basic unit of all living things, from bacteria to humans. As Antoine Lavoisier said: “in Nature, nothing is created, nothing is lost, everything is transformed”.  I’m going to talk about the fate carbon and why it matters in agriculture.

A diverse landscape in Mengsong, Xishuangbanna, Yunnan.

When the leaves fall off the trees, they accumulate on the ground and for litter. After a while, the action of small animals, fungi and bacteria will transform the litter in humus: a dark material made of unrecognizable remnants of leaves, dead microorganisms and animal feces (yes, you’re walking on poo every day!). The difference between humus and litter is the stage of decay at which they are, but the limit is not very clear.

Litter is organic matter which is being eaten by microorganisms, it is transforming, typically the colorful fallen leaves cover that you can see in the forests during Autumn. Litter is the main source of food for the soil animals and microorganisms. Worms feed on litter, their presence in the soil will guarantee a good soil structure because they spend their life digging tunnels. They eat litter and digest it into smaller particles. Nematodes are very tiny round worms, barely noticeable with the naked eye, they will continue the job and eat smaller pieces. Fungi and bacteria eventually degrade organic matter into humus.

Jingmai Ancient Tea Gardens have a thick litter thanks to the big trees.

Humus is organic matter that has reached its final stage of decay, it is almost as stable as stone, it is what’s left after microorganisms have eaten everything. Humus mixes with the soil particles (sand, silt and clay), this is what makes your soil more or less dark.  It is important to have a lot of organic matter in the soil because it increases the water and nutrients capacity of the soil, the fridge is bigger!
Not only the fridge gets bigger as humus is produced, but it is also steadily filled. If organic matter is mostly made of carbon, it also contains nutrients very useful for the plants: nitrogen, phosphorus, potassium, magnesium, calcium… It works as if you were demolishing a house: you couldn’t reuse the concrete, but you could recycle the copper from your electric wires and use it in a new house. Nature works the same, as matter decays, nutrients are made available to the plants.

The soil in Jingmai has a dark color, it is rich in organic matter.

Chemical fertilizers are very handy for the farmers because they are much lighter than organic manure, you need to add up to a hundred times less of for the same amount of nutrients. This is one of the main reasons why they are widely used in the world, from large scale industrial farms to smallholders who don’t have a tractor. They have been the cornerstone of the Green Revolution.

However, their use on the long term creates a major problem: soil degradation. A soil is always degraded because of rain, wind and chemical processes. In order to compensate the losses, you have to continuously add things; this is especially true when it comes to organic matter. After several years without adding organic matter, the soil structure is impacted; it is more vulnerable to weathering and has poorer nutrient and water retention capacity. In other words, you have plenty of food, but your fridge is very small…