Why is Pu-erh Tea Compressed? | HOJO Online Speciality Tea Shop

Why are Pu-erh teas compressed? A common answer to this question would be to minimize volume and make transportation easier. However, there is another lesser-known reason.

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

I conducted an experiment to observe the maturation process of Pu-erh tea under different storage conditions. I analyzed the tea after storing it in various environments: some were exposed to ambient air, some were vacuum-sealed, and some used an oxygen absorber to remove 100% of the oxygen. The tea stored without oxygen matured in the most ideal way.

The Pu-erh tea stored in the ambient atmosphere developed an unpleasant musty odor due to aggressive oxidation. In contrast, the Pu-erh tea stored without oxygen developed a sweet flavor reminiscent of honey and produced a sweet, fruity, or sugarcane-like taste with further aging.

Based on these findings, I have concluded that keeping Pu-erh tea in an oxygen-free environment is essential for achieving optimal maturation.

The maturation is different from fermentation

Some people insist that the maturation of Pu-erh tea is a process of “fermentation.” However, I completely disagree with this idea. Fermentation refers to a chemical reaction mediated by enzymes, but Pu-erh tea that is vacuum-packed contains very low moisture, which is insufficient for any enzymatic reaction to occur. Of course, if tea is stored in a room with high humidity, it will quickly become contaminated by microorganisms such as mold and bacteria. Even assuming there is no microbial contamination, improperly stored Pu-erh teas can develop musty or earthy flavors if oxidation occurs in an uncontrolled manner.

The maturation of tea involves no enzyme and no microorganism

Maturation of tea involves a non-enzymatic oxidation and reduction process that alters the constituents in the tea leaves. When tea is exposed to the oxygen in the atmosphere, it triggers excessive oxidation, which leads to the tea becoming oxidized and spoiled. Therefore, an ideal environment for tea maturation is one without oxygen. One might wonder, then, how the tea can mature or oxidize when there is no oxygen. In chemistry, there are three definitions for oxidation, which are as follows:

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

As you can see from the above three definitions, we do not actually need the oxygen in the air to carry out the maturation (oxidation) process. If you wish to learn more about the definition of oxidation, please refer to the following page:http://www.chemguide.co.uk/inorganic/redox/definitions.html

Both compression and suction can remove oxygen

Let’s rewind to the reason why we need to compress Pu-erh tea. Usually, if one wishes to completely remove the oxygen in the tea leaves, it is either vacuum-sealed or compressed very hard. Both compression and suction can eliminate oxygen if the pressure is strong enough. Most Pu-erh tea manufacturing locations in Yunnan are deep in the mountains, where it can sometimes take more than 20 hours by local bus from Kunming to reach the destination. The practice of compressing tea originates from the wise ancient Yunnan people, who wanted to ensure that oxygen was completely eliminated from the tea. Additionally, the compressed tea made transportation more convenient. Although the leaves at the surface of the Pu-erh cake will inevitably be oxidized, the volume of the tea leaves on the external layer of the cake is considered very minor and negligible.

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.