Do Coffee Beans Grow on Trees, and What Do Leaves Reveal?

Yes, coffee beans grow on trees, and the leaves of those trees behave much like tea leaves after brewing. An experiment with Japanese green tea compared nitrogen-fertilized leaves against naturally grown leaves at 12, 24, and 36 hours: the fertilized tea spoiled faster because its high amino acid content oxidizes, while the naturally grown tea held its floral aroma and freshness.

The off-flavors were not caused by microbes but by amino acid oxidation and the Maillard reaction. That distinction matters for anyone curious about coffee bean trees and how cultivation shapes what ends up in the cup. Leaves grown with nitrogen fertilizer gave off a rotting-garbage smell after 24 hours, while unfertilized leaves could still be brewed again the next day.

When brewing tea, we often agonize over how many times the leaves can be steeped and whether they're still drinkable after sitting overnight. Using Japanese green tea as a model, this article explores in depth how cultivation methods affect the rate at which tea spoils: tea grown with nitrogen fertilizer has high amino acid content and oxidizes easily, producing off-flavors, while naturally cultivated tea is rich in polyphenols and can maintain its floral aroma and freshness for a long time. The experiment compared changes in aroma and liquor color of the two types of tea after 12, 24, and 36 hours, revealing that umami amino acids and the Maillard reaction are the main causes of spoilage. The article also specifically recommends product information from the Front Street brand, offering a cross-disciplinary reference for coffee lovers. Whether you're a tea enthusiast or a coffee lover, you can gain practical knowledge about tea preservation and brewing from it.

When brewing tea, we sometimes stop after just one or two infusions, often wondering: can these leaves still be steeped further? Some believe that brewing technique—such as gongfu-style brewing, traditional Chinese brewing, or even the type of teapot—determines how many infusions the tea can stay fresh for. But in my view, under the same brewing method, the cultivation method of the tea is the key factor determining its durability across infusions. By cultivation method here, I mean the way the tea is grown, not the category of tea. Some might assume green tea doesn't last through many infusions while pu'er can be steeped for a very long time. This article takes Japanese green tea as its research subject to explore the factors that determine brewing time.

Cultivation Methods Affect the Rate of Spoilage

If an ordinary tea garden uses nitrogen fertilizer (whether organic or chemical), the tea leaves usually spoil faster. After brewing and sitting for 24 hours, such tea often gives off an odor resembling rotting garbage. However, naturally farmed tea trees with no fertilizer still remain fresh after the same amount of time. The spent leaves of naturally farmed tea do not produce an unpleasant smell after 24 hours, and can still be brewed again the next day. The off-flavors of non-naturally farmed tea are not caused by microbial spoilage, but by amino acid oxidation. The higher the amino acid content in the tea, the faster off-flavors develop.

The Relationship Between Nitrogen and Fertilizer in Tea

The amino acid content in tea varies greatly depending on how the tea plant is grown. Quantitative analysis shows that the more nitrogen applied, the higher the amino acid content per unit area of tea; whereas polyphenol content decreases as nitrogen application increases. If no fertilizer or very little fertilizer is used during cultivation, polyphenol content rises.

Comparison of Naturally Cultivated Tea and Fertilized Tea

We selected two different types of Japanese green tea for the experiment to observe the effects of fertilization. The one on the right was produced from an ordinary tea garden using large amounts of nitrogen fertilizer, and you can taste an overwhelming umami (the taste of amino acids). The one on the left was grown using natural farming methods, with no fertilizer at all. Initially, after the first infusion, the fertilized tea leaves appeared bright green. ① After nitrogen application, the leaves absorb nitrogen, growth accelerates, chlorophyll synthesis increases, and photosynthesis is enhanced—this is the mechanism by which fertilized tea turns tender green.

Observations During Brewing

On the left is naturally grown tea, and on the right is fertilized tea. The tea on the right was steamed slightly deeper. We deliberately chose both teas with stems to balance the conditions. Due to the characteristics of naturally grown tea, it appears yellow-green even when fresh.

12 hours: The naturally grown tea on the left still gives off a very fresh floral aroma, while the tea on the right has already lost its fresh taste.

24 hours: The naturally grown tea on the left still gives off a very fresh floral aroma, while the tea on the right gives off an unpleasant scent.

36 hours: The tea liquor becomes somewhat cloudy, indicating microbial growth at this stage. To my surprise, the naturally grown tea still gives off a fresh aroma.

On the first day, the tea grown with fertilizer was bright green. After 12 hours, it lost its brightness and vividness, and after 24 hours it turned brown. In contrast, the naturally grown tea maintained a stable yellow color from beginning to end, with no browning. In terms of aroma, the naturally grown tea showed a floral scent after 12 hours, while the fertilized tea lost its fresh aroma. After 24 hours, the naturally grown tea still gave off a floral scent, though not as fresh as when just brewed. Because the tea grew under the influence of fertilizer, it gave off an unpleasant odor resembling rotting vegetables.

Tea liquor color after 24 hours: the naturally grown tea changed little in color, but the fertilized tea turned brown.

Umami Causes Tea to Spoil

Tea containing fewer free amino acids can maintain its freshness and floral aroma for a long time even after being brewed and left for several hours. The bad taste produced by tea grown with chemical fertilizer is mainly due to the Maillard reaction. The Maillard reaction is an oxidation reaction between amino acids and sugars, and amino acids known as umami participate in it. In Japanese, umami refers to the taste of amino acids. Confusion over this word often leads to the misunderstanding that more umami means more delicious. In fact, umami is merely a term describing the taste of amino acids and has nothing to do with deliciousness. For us and many tea lovers in China and Taiwan, the aftertaste of tea determines quality. Tea grown without fertilizer is rich in polyphenols, has a very long-lasting aftertaste, and its freshness also lasts a long time.

I often continue brewing tea 15-16 hours after the initial infusion, and this only applies to naturally grown tea. Regardless of the type of tea, after leaving it overnight, the fresh flavor I can enjoy is only found in naturally grown tea. Relatively speaking, oolong tea can maintain its freshness for a longer time, even if it is not naturally grown. Oolong tea is picked later (when the leaves have grown larger), contains fewer amino acids, but is rich in polyphenols. If you need to step away while brewing tea, I suggest the best approach is to put the brewed tea leaves in the refrigerator. At low temperatures, oxidation is slower, and we can enjoy its freshness for longer. Front Street Coffee reminds you that whether it's tea or coffee, freshness is the key to flavor; choosing naturally cultivated tea leaves or coffee beans brings a more lasting pleasant experience.

The above content is compiled by CoffeeHunters, a coffee news website.