Tea Chemistry
Polyphenol Oxidase (PPO, Phenolase)
Many fruits and leaves contain the enzyme polyphenol oxidase, which is released when you cut the fruit. The enzyme reacts with the oxygen in the air, and this reaction causes the fruit or leaves to turn brown. The enzyme is seen as a defense mechanism against animals that eat the fruit, making it less palatable. It also forms an antibacterial layer that can protect the plant from bacteria, allowing the fruit/tree to heal better.
This chemical process is important for the production of coffee, chocolate, and tea, and it helps to extend the shelf life of the finished dried tea.
What are Catechin Antioxidants?
Catechins are better known as antioxidants and are found in fruits such as grapes (also in wine), chocolate, apples, but mainly in freshly picked green tea leaves from the tea plant Camellia sinensis. These compounds are not necessary for the plant’s growth but are essential for the plant’s health.
We know that when well-established trees are pruned, a sap forms at the wound. This sap is catechins, which help the tree heal its wounds and protect it from insect attacks and infections.
Our bodies cannot produce catechins, so we obtain these compounds through fruits and vegetables, with the tender, freshly picked green tea leaves containing the highest amounts of catechins. Scientists have been particularly focused on a specific catechin called EGCG, better known as epigallocatechin-3-gallate, which is found in many types of dietary supplements. EGCG is especially present in white tea, but also in green, yellow, and sheng puerh tea.
Catechins are also responsible for the bitter compounds in tea. The larger the leaf is allowed to grow, the more bitter it will become. This can be compared to Danish peas. When we pick peas early in the season, they are sweet and delicate; if we let them grow until they are large, we experience them as bitter.
When the leaves are allowed to oxidize, a chemical change occurs in the catechins, which are transformed into thearubigins and theaflavins, giving the tea its red color. These compounds also contribute to the flavor of black and Oolong tea and have a warming effect on the body, which is why it is good to drink black, Oolong, and shu puerh tea in the winter.
Caffeine
One of the big questions is how much caffeine is in tea. There are many different answers to this question, depending on whom you ask – the tea producer or the tea merchant. We traveled with one of the world’s leading tea botanists from Yunnan University in China and asked him how much caffeine tea contains. The answer is not straightforward, but we will try to explain in the next section.
The caffeine content in tea depends, among other factors, on the age of the plant; the older it is, the less caffeine it produces.
Age
It is the age of the plant that determines how much caffeine is in the tea. Caffeine is a natural pesticide that forms in the plant’s roots and is transported to the young shoots to protect them from insect attacks. Studies have shown that there is more caffeine in young tea plants than in old tea plants. In the young plants, caffeine helps protect the plant’s ability to survive potential attacks from insects and animals by affecting their nervous systems, causing them to collapse and die. We humans also feel the effects of caffeine if we drink too much coffee or low-quality commercial tea. Once the plant is well-established, meaning 30 years or more, it stops producing caffeine.
The older the tea plant becomes, the less yield it produces. Commercial tea gardens replace tea plants with new bushes every 10 years to achieve a greater yield (they focus on quantity over quality). Gardens that focus on quality retain the older bushes due to their flavor, even though they yield less. They prioritize quality over quantity.
Several of Simply Tea’s teas come from very old – some up to several centuries old – tea trees in Yunnan. This applies, for example, to our heavenly Rare Yunnan black tea.
Tea bushes that grow high up in the mountains contain much more L-theanine than tea grown in lower-lying areas.
L-theanine has a proven calming effect on the brain and engages in a positive ‘dialogue’ with caffeine. Together, L-theanine and caffeine create the unique effect of calming the brain while also enhancing focus.
L-Theanine
A crucial element for whether the body absorbs caffeine is the compound L-theanine, which is a non-protein amino acid. This amino acid has a remarkable effect on caffeine, as it essentially “resets” the negative effects it has on the body. The more L-theanine in the tea leaf, the less effect caffeine has on our nervous system. Therefore, many tea merchants say that white tea has the lowest caffeine content, but in reality, it can easily be among the teas with the highest caffeine content. This is because Silver Needle (Sølvnål), a white tea, often has a very high content of L-theanine, which is why we do not feel the effects of caffeine; instead, we experience the calming effect caused by L-theanine.
L-theanine is found in tea plants that are grown on mountaintops in China and in the Himalayas (e.g., Darjeeling). L-theanine is often found in tea plants grown at elevations over 1000 meters or where surrounding plants or trees provide shade, such as bamboo forests or rainforests, or because they are covered by a natural cloud layer.
“Kabuse”
Several Japanese tea producers cover their teas with bamboo, rice, or cloth mats about 20 days before harvesting. This process, known as “kabuse,” helps to stress the plant and forces it to produce large amounts of L-theanine. L-theanine, which is found only in tea and a single species of mushroom, is the most sought-after component in tea. It is what tea enthusiasts seek because it gives the tea its sweet flavor and long, rich aftertaste, referred to as “umami,” as well as an indescribable sense of well-being.
Early Harvested Buds
The highest concentration of L-theanine is found in the buds, such as Silver Needle and Yunnan Golden Buds, or in green teas like Anji Bai Cha. L-theanine is what we at Simply Tea look for when selecting teas on our annual trips to China. Additionally, it is found in high-quality Matcha, Gyokuro, Sincha, and Sencha from Japan. These teas also have a very high caffeine content. Since Matcha tea is a concentrated powdered green tea, it contains seven times as much caffeine as tea brewed from leaves, but due to the L-theanine, it has both calming and invigorating effects on our nervous system.
To summarize:
- All tea contains caffeine.
- If you buy decaffeinated tea, it is also stripped of all other beneficial nutrients, and there is still about 10 percent caffeine left in the leaves.
- Tea from tea bushes or trees that are more than 30 years old contains almost no caffeine. The tea merchant may not know much about this unless they are involved in the harvest, which we are. This applies to our Rock Oolong teas and most of our Puerh teas, where the tea gardens are more than 30 years old—some can be several hundred years old. These teas are highly sought after and valuable in China. They are difficult to find in Europe but are available at Simply Tea, the only place in Denmark.
- Commercially grown tea in tea bags, and tea that is enhanced with flavorings, flowers, fruit, and oils, will be experienced by the body as containing a very high amount of caffeine, as there is no L-theanine to counteract the effects of caffeine.
- Tea made from buds harvested early in the spring and grown in areas where the altitude creates a natural cloud cover will feel the most calming to the body, despite the caffeine content in these teas being high—L-theanine essentially “resets” the caffeine.
Learn more at a tea tasting course
Tea is quite a complex plant with more than 550 different nutrients. If you are interested, we will share more about caffeine at our weekly tea tasting courses.
L-Theanine
L-theanine (γ-glutamylethylamide) is a unique amino acid that is found exclusively in the tea plant Camellia sinensis. There is a single mushroom species, Xerocomus badius, that also contains this compound.
After water, tea is the most consumed beverage on the planet, which means that a significant amount of theanine is ingested worldwide on a daily basis. L-theanine is a very important element for the flavor of tea and is the taste we refer to as umami. Tea contains many nutrients, including polyphenols, proteins, amino acids, vitamins, and minerals. Of the dried tea’s weight, theanine makes up about 1-2%, which corresponds to approximately 50% of the amino acids in tea. Theanine is developed in the roots of the plant and concentrates in the leaves, where sunlight converts theanine into polyphenols. Because of this, many farmers grow their tea plants away from direct sunlight to preserve the theanine content and thus the flavor.
Chemistry
In 1949, L-theanine was discovered in green tea by a Japanese researcher named Sakato, and in 1964 it was approved as a food additive. Theanine is water-soluble and is quickly absorbed in the small intestine when consumed.
Mechanisms of Action
In the brain, L-theanine increases the production of dopamine and serotonin, which are mood-enhancing neurotransmitters. Theanine increases alpha (α) wave activity, which is a sign of induced relaxation; therefore, we experience a sense of well-being shortly after consuming a cup of tea. Even though there is caffeine in the tea, we feel a relaxed state of mind without becoming tired. Apparently, theanine resets the effects of caffeine on the nervous system and reduces the stress hormone cortisol. L-theanine is also associated with improved learning, concentration, and memory abilities.
Is L-theanine found in all tea?
Unfortunately, it is not. The quality of tea leaves used in Europe is harvested so late in the year that L-theanine will either not be present or will be in such low concentrations that it will not be significant for us.
For tea to contain the amino acid L-theanine, the leaves must be harvested before photosynthesis occurs. As soon as photosynthesis takes place, the amino acids are converted into polyphenols (tannins). Tea that is harvested early in the spring and is protected from sunlight contains the highest amounts of amino acids. This explains why teas that are harvested early in the year, such as Darjeeling (First Flush), are so sought after.
If you want a tea where the amino acids are preserved, you should choose a bud tea that is harvested early in the spring. These teas, which have very tender leaves, are among the most expensive in the world and account for only about 10% of all teas produced globally.
If you want to experience these teas, you can confidently choose teas from Simply Tea. We ensure that amino acids are prioritized when we purchase our teas in the spring. We are involved in assessing the quality together with our partner Seven Cups before we order the year’s harvest.
What is Umami?
Umami is a Japanese word that means delicious, and it has recently been recognized by Western researchers as the fifth taste experience, alongside sour, sweet, salty, and bitter. Just a few years ago, studies proved that our mouths contain taste receptors for this irresistible savory flavor known as umami. The other four “basic tastes” have been widely accepted for about a couple of thousand years.
For tea enthusiasts, a preference for umami is the most important element and something associated with tea of particularly high quality.
Can Everyone Taste Umami?
Most people are not familiar with umami, and the flavor itself is very delicate, often highlighted in conjunction with other flavors. Our taste senses consist of five basic tastes – sour, sweet, salty, bitter, and umami – with other related tastes being spicy and astringent.
When one learns to taste food carefully, one also learns to identify “umami.” Most chefs know that umami is an important part of creating the best culinary experience.
Umami arises when certain amino acids are present, and glutamates are often released due to specific chemical changes during processing.
There are about 20 different types of amino acids in teas. Geography, altitude, season, weather conditions, plant variety, and processing methods all play an important role in the amount of these compounds.
How Does the Plant Develop Amino Acids?
Amino acids are formed in the roots of the tea plant Camellia sinensis var. sinensis and Camellia sinensis var. assamica and accumulate in the buds as early as spring.
In areas where the plants grow high, about 1000 meters above sea level, and are naturally shaded from direct sunlight—either by clouds, trees, bamboo, rainforests, or manually shielded—photosynthesis is prevented from developing; thus, these valuable amino acids are retained in the highly sought-after buds.
In countries like China, where the tea plant grows everywhere on mountaintops and in the Himalayas in India, these teas can be found. We know them as, for example, Anji Bai Cha, sheng Puerh, and first flush Darjeeling.
In Japan, because the natural conditions are not present, the plants are shaded about 20 days before harvest under tent-like covers or bamboo mats. The tea bushes respond by developing very soft and thin, deep green tea leaves that struggle to capture sunlight. The plant is stressed, and thus the special amino acids are developed. This processing method is called “kabuse.” Examples of kabuse tea include Matcha and Gyokuro.
How Many Amino Acids Are in Tea?
Of the total dried weight of tea, amino acids make up about 2%.
Approximately 50% of the amino acids that are unique to tea are called theanine and are found in the L form (L-theanine). Of the 20 amino acids, these 6 components account for more than 90% of the total amino acids in tea: theanine, aspartic acid, arginine, serine, glutamine, and glutamic acid.
What Do Amino Acids Mean for Flavor?
Aside from the many health benefits that amino acids provide, they also contribute to giving tea its unique flavor and the experience of umami that all tea enthusiasts, tea connoisseurs, and gastronomes seek.
The following amino acids provide the sought-after flavor experiences in tea:
- Theanine is experienced as sweetness and umami.
- Aspartic acid is experienced as sour.
- Glutamic acid is experienced as sour and umami.
- Arginine is experienced as astringent.
- Glutamic acid and arginine are experienced as a strong umami.
Previously, it was believed that L-theanine was solely responsible for the umami flavor, but recent studies on the quality and taste of amino acids show that while L-theanine has sweetness, it does not have a particularly strong flavor. L-theanine is found in very high-quality teas, but it is not the only amino acid that contributes to the umami flavor.
Glutamic acids account for about 20-30% of amino acids but contribute to a very powerful umami flavor experience.
The Japanese researcher Dr. Muneyuki Nakagawa wrote in his 2007 article (unfortunately, it is only available in Japanese) that studies show that arginine is related to the umami of the Japanese tea Gyokuro, which has a very different umami flavor from, for example, the Chinese tea Anji Bai Cha, which, in turn, has an exceptionally high content of L-theanine. Here, one must conclude that the umami flavor experience develops due to a combination of amino acids and not just a single one.
What is Astringency?
Astringent or astringency is unfortunately lacking in the Danish language, and instead, the word “astringens” is used to describe the sensation many experience when tasting wine, beer, chocolate, tea, fruit, or vegetables.
Astringency means constricting, sharp, or biting. The flavonoids in tea, better known as tannins, react with the drinker’s saliva in the mouth, and this sensation should not be confused with sourness or bitterness.
When eating an unripe banana, one experiences a drying sensation in the mouth, which is astringency. This can feel uncomfortable for many, but if the sensation is followed by saliva production—what we experience when the mouth waters—it is clearly a desirable feeling and an important parameter for assessing the qualities of the tea. Astringency can be felt all the way back in the palate and throat, which is why one must swallow the tea to get the full flavor experience.
We taste: sour, sweet, salty, bitter, umami, and perceive astringency.