Oxidation may give black tea nutritional benefits that are not present in green tea. For example, the nutrients in black tea may reduce the risk of several cancers, protect the heart against atherosclerosis, and help maintain healthy blood pressure.
Oxidation is a process through which tea leaves are exposed to the air in order to dry and darken, contributing to the flavor, aroma, and strength of different teas. Just as other fruits and plants, like apples or avocados, brown when exposed to oxygen, tea leaves go through a similar process after they are harvested.
Oxidation refers to a series of chemical reactions that result in the browning of tea leaves and the production of flavor and aroma compounds in finished teas. Depending on the type of tea being made, oxidation is either prevented altogether or deliberately initiated, controlled and then stopped.
Tea leaves which are fully oxidized will turn brown and black, while tea leaves that are not oxidized at all will remain green.
Tea oxidation also affects caffeine content, which affects bitterness. Unlike catechins, processing tea leaves does not turn caffeine into new, less bitter molecules. Instead, the process used to halt oxidation removes caffeine from tea leaves, which reduces their overall bitterness.
A dark cup and one of the most popular teas is black. This has had the longest oxidation of any tea and is sometimes enjoyed with a splash of milk. Oolong tea is what is produced after an 80% oxidisation and green tea is usually unoxidised to help retain a light fresh taste.
Green tea does not undergo any form of oxidation. Instead, its leaves are slightly steamed or pan-fired after harvesting to stop oxidation and withering, which gives it a bright green color and vegetal taste. After this, the leaves are rolled into their final shape and dried.
Oxidation may give black tea nutritional benefits that are not present in green tea. For example, the nutrients in black tea may reduce the risk of several cancers, protect the heart against atherosclerosis, and help maintain healthy blood pressure.
Since rooibos is oxidized in a similar fashion to black tea, it is more shelf stable than some teas and herbs and can technically stay fresh and drinkable for up to two years.
This is primarily because the antioxidants in tea, called polyphenols, begin to degrade after the tea is brewed. While some tested examples of bottled teas contain moderate levels of antioxidants, it's safe to say that the longer it's been sitting on the shelf, the fewer polyphenols it has.
When it comes to tea, green tea gets the gold. “Green tea is the champ when it comes to offering health benefits,” says Czerwony. “It's the Swiss Army knife of teas.
Oxidation(Fermentation)
In a fermentation chamber with room temperature set at 25-26°C and humidity at 90%, tea leaves are spread evenly to a thickness of 4-5 cm and left to ferment for 2 to 3 hours. During this process, the green leaves turn a bright reddish-bronze color, and a tea-like aroma waft through the air.
Drinking tea every day is a healthy habit that may benefit your health in various ways. Not only is it a low-calorie drink, but black, green, oolong and white teas contain unique compounds like flavan-3-ols that support heart health.
The Process of Oxidation
These compounds contribute to the dark color of oxidized teas, but they also contribute to flavor. While catechins are often identified as bitter, theaflavins and thearubigins contain astringency without bitterness. Theaflavins, in particular, are also associated with 'richness' of flavor (7).
In most cases, old tea will simply be less flavorful than it should be, and taste dull or stale. While old tea isn't usually dangerous to consume, it's definitely a less than ideal tea drinking experience. If your tea tastes like it's gone bad or if you spot visible mold or other signs of decomposition, steer clear.
Black tea go though the full-oxidized process. In the course of chemical oxidation, catechine transform to theaflavin or thearubigin, and vitamin C is largely destroyed. The major black tea producing countries are India, Kenya, Sri Lanka, and Indonesia. Those countries produce 75% of the total production of the world.
*People with estrogen-sensitive cancers, such as breast cancer, should avoid rooibos tea or consult a physician before doing so. According to one study, consuming large volumes of rooibos tea on a regular basis raises liver enzymes, which may create problems with liver tissue and function.
Rooibos tea is known to relieve allergies, irritated skin, and stomach cramping. Its' vast supply of antioxidants makes it a star fighter against cancer, and helps slow the aging process and boost the immune system. This tea contains no oxalic acid, making it the best tea for those prone to kidney stones.
The concentration range of the determined heavy metals in rooibos tea samples were as follows: Cr (0.17-11.98 mg/kg), Fe (31-450 mg/kg), As (ND-0.51 mg/kg), Cd (0.09-0.17 mg/kg), and Pb (0.06-2.73 mg/kg). Cr was found in higher amount when compared to the World Health Organization (WHO) permissive limit (1.3 mg/kg).
Although all black and white teas contain interesting antioxidants, green tea is the most powerful, particularly because of its high catechin content. In the family of green teas, matcha tea is the richest in antioxidants.
For both, the flavor becomes smoother, more mellow, and thicker with age. Furthermore, well-aged black tea 10 years or older is a popular Chinese herbal remedy for coughs. Jasmine Pearls green tea being mixed with fresh jasmine flower blossoms to absorb their aroma.
There are two things that can be done to halt oxidation: 1) denature oxidation enzymes or 2) displace oxygen. 1) Denaturing the oxidation enzymes entails treating raw tea leaves with heat. This occurs in two different stages: the “enzyme kill” stage and the “final firing” (drying).
Research has suggested that the antioxidant effects of rooibos are similar to, if not quite as strong as, those of green tea. A recent study on the rat model has suggested that the antioxidants in rooibos tea may protect the liver from oxidative stress, helping to render this organ more resilient to induced damage.