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Why is Pu-erh teas compressed? A common answer to that question would be to minimise the volume and for effortless transportation of tea. However, there is another reason that is not widely known.

No oxygen is an ideal environment for maturing Pu-erh tea

I have conducted an experiment of keeping Pu-erh tea for maturation. I analyze the tea condition after keeping the Pu-erh teas in different conditions where some were exposed to ambient atmosphere, some vacuumed, and some using an oxygen absorber to remove 100% of oxygen. As a result, the tea that was kept without oxygen matured in the most ideal way. The Pu-erh tea kept in an exposed condition to the ambient atmosphere absorbs the moisture present in the air; developing some mold on the surface or emitting unpleasant musty odor. On the other hand, the Pu-erh tea that was kept without oxygen developed a sweet flavour that reminds me of honey, and it produced the sweet fruity or sugarcane-like flavour with further storage. Based on these experiments, I have concluded that it is necessary to keep Pu-erh tea without oxygen in order to get it matured very well.

The maturation is different from fermentation

There are some people who insist that the maturation of Pu-erh tea is a process of “fermentation”. However, I absolutely disagree with it because fermentation refers to the chemical reaction that is mediated by enzymes. However, the tea that is vacuum packed contains very low moisture that is insufficient for any enzymatic reaction to occur. However, if tea is kept inside a room with high humidity, it will immediately be contaminated by microorganisms such as mold and bacteria. Furthermore, some inappropriately kept Pu-erh teas would produce musty or earthy flavour if any of them were actually contaminated by the microorganism during storage. Of course, there is a big question mark whether or not it is safe to consume.

The maturation of tea involves no enzyme and no microorganism

Maturation of tea is neither by enzymatic reaction nor microbiological fermentation; but, it involves a non-enzymatic oxidation and reduction process which occurs by altering the constituents in tea leaves. When tea is exposed to the oxygen in the atmosphere, it triggers excessive oxidation. As such, tea will be nothing but oxidized and spoiled. Hence, an ideal environment for having tea matured is without oxygen; yet, one may wonder how would the tea be matured or oxidized when there is no oxygen. In chemistry, there are three definitions for oxidation which are as follow:

  1. Receive Oxygen
  2. Release Hydrogen
  3. Release Electron

As you can see from the above three definitions, we do not really need the oxygen in the air to carry out the maturation (oxidation) process. If you wish to learn more about the definition of the oxidation, please refer to the following page:

Both compression and suction can remove oxygen

Let’s rewind back to the reason why we need to compress the Pu-erh tea. Usually, if one wishes to completely remove the oxygen that exists in the tea leaves, it is either vacuum it or compress it very hard. Both compression and suction could eliminate the oxygen if the pressure is strong enough. Most of the Pu-erh tea manufacturing places in Yunnan are located deep inside the mountains where it sometimes take more than 20 hours by local bus from Kunming to reach the destination. The idea to compress tea originates from the wise ancient Yunnan folks who wanted to be certain that oxygen was completely eliminated from the tea; moreover, the compressed teas enable a more convenient transportation. Although, the leaves at the surface of the Pu-erh cake will definitely be oxidized; however, the volume of the tea leaves at the external layer of the cake is considered as a very minor amount which is small enough and negligible.

pu-erh tea

The Pu-erh tea cake used to be compressed very hard

About 20-30 years ago, the Pu-erh tea was often compressed extremely hard that it was known as the “iron bing” (铁饼). It was compressed as hard as a piece of stone that one cannot even break it using a knife or a strong eyeleteer. Based on my experience, all the iron bing Pu-erh tea was ideally matured no matter how it was kept. Thanks to the hard compression, there was no oxygen remaining inside the leaves. These teas produced sweet flavour like dried fruits which I enjoy drinking them so much. Unfortunately, nowadays most of Pu-erh teas are not compressed like an iron bing anymore. If we compress our tea too hard, we would receive a number of complaints from the customer saying that it is really very hard to break apart the tea for drinking. Generally, nowadays most of tea companies compress Pu-erh tea moderately, which will definitely leave some oxygen in the tea leaves. Under the circumstances, tea will get oxidized no matter how it is kept.

Based on the above logic, we pack tea with an oxygen absorber that is made of the reduction iron powder. This will absorb oxygen as iron absorbs the oxygen from the atmosphere to form iron oxide. We are quite satisfied by this method since we can get the tea well-matured in a right environment and at the same time, the Pu-erh tea cake will not be too hard to cause nuisance to the customers.

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