Tea Fermentation vs Oxidation – Knowing The Difference

tea fermentation vs oxidation – knowing the difference
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Tea is one of the most popular, refreshing and delicious beverages that makes us active and healthy. It is the first drink that many of us expect after a good nights’ sleep or when we are stressed and tired working in the office or other places. We enjoy tea in different varieties and it also comes in different colors. 

We have seen green tea on the one hand and on the other hand we also must have certainly comes across tea leaves and tea dust that is black or brown in color. While the color of green tea is understandable given the fact that the tea leaves are green, we might wonder why many varieties and kinds of tea are black or brown in color. 

The color of our favorite tea could be black because of a number of reasons. It could be because of the quality of the tea as well as the age of the tea. We also could come across black tea with a tinge of brown color in it. The process of tea-making also has a role to play in the color of the tea that we enjoy with our family members and friends. 

We could have seen some articles or heard some news clippings that talk about the process of fermentation that might be the reason for such changes in colors. While tea leaves could turn brown through a process of fermentation, this may not be fully true. Tea also goes through a process called oxidation. Those who are conversant with the process of making tea will certainly agree that it is oxidation and not fermentation is the main reason that leads to the color of tea becoming brown.

Why Does The Color Change?

To understand the reasons for change of color from green to brown or from brown to black, we need to know the main difference between oxidation and fermentation. Let us get started by understanding something more about fermentation. Fermentation is a unique method of microbial metabolism. Fermentation helps in converting sugar into acids, alcohol and gases. This is a process that is done with the specific objective of producing a particular chemical product or various by products. There are a few special characteristics of this process of converting sugar into various products and byproducts. 

Fermentation could lead to lactic acid fermentation and that is quite common. This process is used for producing yoghurt out of milk. We then have alcohol fermentation that is used for making wine, whiskey and other drinks from fruits and other substances.While we are mostly bothered with the end products, we often tend to ignore the importance of starting materials.We need to understand that the process of fermenting can be done with or without oxygen. There is a need for yeast or bacteria (living, catalytic organisms) to help in the process of fermentation. The process is highly complex and there are different steps that must be completed before we reach what is referred to as complete and total fermentation.

What Is Oxidation?

Oxidation is also an enzymatic and biochemical activity. The most common impact of oxidation is perhaps that of free radicals. If you cut a fruit like apple or a vegetable like potatoes and keep the cut portion out in the open, you will notice that within a short period the natural color of the apple or potato changes to brown and then eventually to black. The fruit or vegetable also become soft over a short period of time. This is what oxidation all about. It happens when the host material starts absorbing oxygen and this leads to the transformation that is chemical and enzymatic in nature. As with fermentation, oxidation also has some important features and characteristics that should be kept in mind. 

Oxidation can be controlled or it can be spontaneous.This process could lead to negative as well as positive changes. It is also possible to complete oxidation through a single step transformation process. When the process is completed through a single step process, it could happen within a short period of time.Apple and potato turning brown and then to black is a simple example of negative oxidation that is spontaneous. On the other hand if slices of potato, apple or banana are dried up in a controlled environment and processed (perhaps in a dryer) then we could have a positive oxidation happening.

Is There A Need For Oxidizing Tea?

Whether we may be aware or not, there is no doubt that spontaneous and immediate oxidation starts the moment the tea leaves are plucked from the plants. The process continues and goes on as far as black, white, oolong and other colors and varieties of tea are concerned. it is therefore, common to see manufacturers pan fry or dry the green or white tea as soon as they are plucked from the gardens. This is done to stop any further scope or possibility of oxidation. De-enzyming of tea leaves is also a vital process for converting raw tea into tea that is suitable for drinking as beverages. This process involves application of heat because it stops the various activities of the enzymes. When this happens, the poly-phenols retain their original color. Hence, this perhaps explains the reason why green tea continues to remain green even after it goes through the above processes. 

On the other hand, controlled oxidation is also used and this is what helps in turning the color of the tea from green, white or oolong to brown or black as desired. Understanding the difference between controlled oxidation and spontaneous oxidation is critical for knowing the reasons for change of colors as far as raw tea to packed or ready-to-drink tea is concerned. 

How Is Black Tea Made?

Black tea is produced when the withered tea leaves are crushed, torn, cut and also rolled. This results in faster and rapid oxidation. This process results in some noticeable changes. It causes damage to the cell walls of the tea leaves. Oxygen gets in contact with the exposed leaves and cells that have been damaged through this process. This results in the tea leaves turning into brown color. The process of rolling operations or CTS hastens the process of oxidation even further.

What Is The Difference Between The Two

Now that we have a reasonably fair idea about fermentation and oxidation, finding out the basic difference between the two would also not be a big problem. However, we need to understand some basic attributes that differentiate fermentation and oxidation with specific references to tea.

Fermentation requires some preconditions like the presence of bacteria or yeast. However, this is not the case as far as oxidation is concerned. Oxidation can happen when freshly plucked tea leaves get in contact with oxygen-rich and moist air. Black tea making has got to almost everything with oxidation and there is perhaps no role as far as fermentation is concerned. Fermentation however may have a vital role to play. The process involves exposing the tea leaves to humidity. When humidity and oxygen in the air work together, this leads to production of reactivated and oxidized enzymes. This could help quite a bit in altering the flavor and aroma of tea. It also helps in mellowing the tea. Tea leaves plucked straight from the plants are bitter and have an astringent flavor. The process of fermentation helps in making the tea feel good in our mouth and it attracts our taste buds.Fermentation process has to be done carefully and under very carefully controlled environments. This should include the right air flow, humidity and other such things. The quality of air should also be good. When it is done this way, the tea changes flavor and color without the risk of being attacked by mold, mildew and various other microorganisms.

Different Tea Varieties Require Different Treatments

When it comes to oxidation, different tea varieties need to be handled differently. White tea requires just around 10% of spontaneous oxidation. Green tea should be kept away from uncontrolled oxidation. However, some bit of spontaneous oxidation does take place and we should not be bothered too much about it. 

Oolong tea on the other hand requires high and controlled oxidation to the extent of 80%. Black tea is the toughest to make because it requires complete oxidation. Only experienced and skilled tea-masters could be able to control and monitor this process. 

Methods Used For Oxidation And Fermentation

Different types of methods are used for oxidation or tea. Floor method is the most common. The tea is spread in thin layers ranging from 5 to 8 centimeters. This has to be done under the careful watch of tea masters. Trough method is done with the use of perforated trays. It is considered efficient because air-flow quantity can be controlled. 

CFM is common as far as fermentation is concerned. CFM stands for continuous fermenting machine. It makes use of a combination of trough and floor methods. Once the process has been completed, the tea masters put the processed tea leaves into a discharge conveyor. When CFM is used, some parameters might need to be changed. The tea master is the best person for making the changes. The parameters could include oxidation period, bed thickness, and volume of air flow and so on. 

The Final Word

In fine, while understanding the difference between fermentation and oxidation could be knowledge-enhancing for us as readers and end-users of tea, the processes involved are quite complex, tough and only experienced tea-makers and other skilled professionals would be in a position to do it.

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Mary L

When you discover something you love you want to share it with the world, that’s only natural. My passion had become my way of life, and I am finally able to share a cup of the good stuff with the ones I love. Proof that dreams really do come true when you can share your favorite brew.

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