Tea is a type of food, and as such, it has an expiry date and is prone to change. When storing tea, we either try to prevent or promote its changes depending on the desired outcome. For teas that emphasize freshness, even slight mishandling during storage can quickly diminish their original flavor. For teas that are prized for their aged aroma, we need to control their deterioration and guide their aging process to achieve desirable flavors, such as camphor, jujube, or medicinal aromas.

How Long Is the Expiry Date of Tea?

Essentially, tea is an agricultural product. All agricultural products have an expiry date, and consuming them past this date can be harmful. This applies to tea as well. Teas do have expiry dates, but many consumers are unaware of this fact, and tea sellers often avoid acknowledging it, which is why many tea packages do not include an expiry date.

The determination of a tea's grade and value is typically done by tea experts through tasting sessions, and the resulting expiry dates may not always be very precise. Therefore, the concept of an “expiry date” becomes somewhat ambiguous, with some saying it's one year, others suggesting half a year, and some not specifying an expiry date at all until the tea loses its flavor completely.

In reality, the national standards for food hygiene have established criteria for tea, including expiry dates. However, there are no national standards set for Pu'er tea due to its nature as a fully fermented product, making it difficult to establish an expiry date. Other types of tea should strictly adhere to these national standards; otherwise, once past their expiry date, they lose their quality and flavor, and if they become damp and moldy, they can be harmful to human health.

The expiry date of tea is related to its quality, and different types of tea have varying expiry dates. For example, Pu'er tea and dark tea improve with age, and their expiry dates can extend up to 10-20 years. Similarly, aged Wuyi Rock Tea develops a rich fragrance and robust flavor. Teas like Hunan dark tea, Hubei Fu brick tea, and Guangxi Liubao tea also improve in quality when stored properly.

This characteristic led to speculation about old teas in recent years, with some aged Pu'er teas being sold for millions of yuan. Speculation is a game for merchants, but ultimately, tea is meant for drinking. If old tea is not stored correctly and deteriorates, it becomes substandard and unsuitable for consumption. For example, Pu'er tea generally requires a dedicated storage room with a temperature around 25°C and humidity controlled at around 70%. Additionally, the storage area must be well-ventilated, free from odors, and the tea should be turned every three months. These conditions are challenging for most tea enthusiasts and collectors to maintain.

Typically, sealed packaged teas have an expiry date ranging from 12 to 24 months. Bulk teas have a shorter expiry date because they absorb moisture and odors more easily, diminishing their original flavor and accelerating spoilage. For example, Green Tea is generally best when fresh, with an expiry date of about one year under normal temperature conditions. However, factors such as temperature, light, and humidity significantly impact tea quality. If stored properly, these factors can be minimized or eliminated, allowing the tea to maintain its quality for longer periods.

To determine whether tea has expired, consider the following: check for signs of mold or an off-flavor; observe the color of the brewed tea, such as whether green tea has turned red or the infusion has become brown and dull; taste the tea for concentration, astringency, and freshness. These assessments can be challenging for non-experts. If you have loose-Leaf tea that has been stored at home for over 18 months, the production date would be even further back, and such tea should be consumed with caution.

What Changes Occur in Tea During Storage?

During storage, many chemical components in tea undergo oxidation, leading to staleness or deterioration.

1. The Influence of Humidity

Chlorophyll content is high in young leaves and can easily lose its green color and turn brown under light and heat. Catechins tend to oxidize during storage, causing the tea to darken. Vitamin C is an important nutrient in tea and is closely related to its quality. It is a substance that is easily oxidized and difficult to preserve. When vitamin C is oxidized, it not only reduces the nutritional value of the tea but also causes it to darken and lose its fresh flavor.

When the moisture content of tea is too low, the tea can become stale and deteriorate. When the moisture content of the tea is around 3%, it is relatively easy to preserve. However, when the moisture content exceeds 6% or the air humidity is above 60%, the color of the tea darkens, and the quality deteriorates. The moisture content of finished tea should be controlled between 3% and 6%; if it exceeds 6%, the tea should be re-fired and dried.

2. The Influence of Temperature

The higher the temperature, the faster the tea will become stale.

For every 1°C increase in temperature during storage, the rate of browning increases by 3-5 times. Storing tea below 10°C can inhibit browning. Storing at 20°C almost completely prevents the aging and deterioration of tea.

3. The Influence of Oxygen

If tea is improperly stored and exposed to oxygen, it accelerates the oxidation process, affecting the quality of the tea.

4. The Influence of Light

Light is a form of energy, and exposure to light can cause chlorophyll to decompose and fade. Exposure to light during storage affects the quality of tea and can render it unsuitable for consumption.