Full post can be read at: https://johnknightphd.substack.com/Intro Imagine a beautiful spring morning. The trees are stunning with new, bright green growth and colorful blossoms. Songbirds fill the air with their melodies. Above, small white clouds drift by across the blue sky. Now imagine feeling the warmth of a mug in your hands as you take in this scene. What’s in the cup? For some, it might be a nice cup of coffee. Others might prefer something herbal or fruity. Still others would drink tea - green tea perhaps! And what if that green tea actually tasted like cherry blossoms? Hello everyone! My name is John Knight. As a chemist and writer, my goal for these audio posts is to peel back the curtain on the chemistry of our modern world. Whether it’s the latest lab breakthrough or the hidden science in our daily lives, I’m here to help break down the science so that it’s clear without getting bogged down in a bunch of lab notes. Before I tell you about a very special kind of tea, just a quick reminder: if you’re listening to the audio-only version, be sure to check out the full post on my Substack. There, you’ll find a transcript of everything I’m saying and important visuals, some of which can help you “see” the chemistry I will discuss. And now, let’s talk about a tea that was rejected by the industrial tea world of Japan, although it tastes like one of the most Japanese things of all… The Fleeting Scent of Spring Cherry blossoms, or sakura in Japanese, are deeply connected to the spring season. The trees are prized for their beautiful flowers that come in shades of white or pink. For many, they are a symbol of renewal and the end of winter. Tourists will often flock to areas with many cherry blossom trees. Just ask anyone who has traveled to Japan or Washington, D.C. at the beginning of spring! These trees are also a symbol of impermanence. Because they only bloom for one or two weeks on average, their beauty is but temporary, much like spring itself. In Japan, sakura are more than just ornamental flowers, however. They actually have a long history of being used in confectionery and seasonal food. Flavor-wise, they are often described as a combination of floral, vanilla, almond, and light cherry notes. This might be confusing to some who have stood close to a cherry blossom tree. If you put your nose right up to a flower, you will probably smell nothing. They are perfectly edible, but you probably won’t taste anything, either. Instead, the flavor is locked up in the flower, and a little chemistry is required to release it. So how does this work? The flowers are traditionally cured through a kind of pickling process. First, the flowers are washed, dried, and mixed with sea salt to remove moisture. This is followed by a thorough soaking in a vinegar made from plums. This not only preserves the flowers and gives them a vibrant pink color but also changes their flavor. Sunlight and Sugar Many plants produce compounds called glycosides, sugar-containing molecules that also contain a non-sugar component. In addition to regulating plant growth and stabilizing pigment molecules, glycosides are also used to store potentially toxic or unstable molecules meant to protect the plant. Plants also produce special enzymes that can break down these glycosides into their individual components when needed. For cherry blossoms, one important glycoside is o-coumaric acid glucoside. That name might sound scary, but bear with me for a moment. Think of this glycoside as a large storage molecule with an important component safely secured inside. On the tree, this glycoside and its unlocking enzyme are never stored in the same place. After harvesting, washing, and curing, however, many of the cells in the flower are broken, allowing the enzyme and glycoside to interact. The enzyme then breaks the glycoside into two molecules: o-coumaric acid and glucose. From there, the rest of the chemistry can happen relatively quickly. That coumaric acid is a rigid, elongated molecule containing what chemists call a trans double bond. Normally, this would be stable, but in this case, it’s not. Add just the right amount of energy into that double bond, and it can be converted into a cis double bond, bending the molecule toward itself. It turns out that ultraviolet light (UV) from the Sun provides the necessary energy to do this. Once the geometry changes, the molecule essentially folds in on itself, placing the atoms in the right position to react and form an important molecule called coumarin. It’s coumarin that is primarily responsible for that sweet, vanilla-almond flavor and scent of sakura. But what does all of this have to do with green tea? That’s a completely different type of plant! And traditional green tea doesn’t contain fermented flower petals… It turns out that this process of making coumarin also occurs during tea production, albeit in very small amounts. For one particular variety, however, this isn’t the case. Japanese Green Tea Many people have a basic understanding of where tea comes from, though they may not be aware of the exact details. Most of the tea consumed in the world is made from the leaves of the tea tree (Camellia sinensis). That’s right - the tea tree is in the same family as all of those glossy, evergreen shrubs that produce bright, showy flowers from fall to spring every year. The processing of the leaves varies considerably from country to country and even region to region. For every producer that uses modern methods of harvesting and processing, it’s not difficult to find some who make tea using more traditional methods and maybe even entirely by hand. Although China is the biggest producer of green tea in the world, Japan also produces its share. It’s also very distinct. When making green tea, it’s important to stop oxidation by enzymes in the leaves. Otherwise, you’ll end up making black tea or oolong tea. In many green tea-producing countries, this is done by pan-frying or even roasting the leaves on a hot surface. In Japan, the leaves are steamed. This gives a completely different flavor profile. Where green teas from China might have mellow, nutty, floral, or even toasty notes, Japanese green teas are more vegetal, grassy, and full of umami flavor. Some producers intentionally shade the trees before harvest, which forces them to produce more flavorful compounds. Japanese producers also love to use machines. In fact, the entire process is mechanical. This is in stark contrast to other countries, where you can still find people harvesting and processing by hand. Japanese Tea Cultivars Now, I mentioned that most tea comes from a single type of tree, but there are many varieties of tea trees worldwide. These are often called cultivars. Think of them as the tea tree equivalent of wine grape varietals. In Japan, there are hundreds of cultivars, and the government has an official registry that recognizes over 130 of them. Despite the large number of cultivars, however, most of the green tea in Japan - roughly 75% - comes from a single cultivar called Yabukita. It’s a mainstay known for its high yields, strong umami flavor, and, perhaps most importantly, its ability to be easily processed using machines. Resilience? It’s got that in spades! Yabukita grows in almost every tea-producing region of Japan, with only the warmest and coldest areas of the country limiting its reach. If you ever drink Japanese green tea, there’s a good chance it’s prepared from Yabukita. Other cultivars exist with their own special characteristics. Saemidori trees mature early and produce a tea with lower bitterness. Okumidori, in contrast, grows better in colder parts of the country. Gokou is kind of like an umami bomb that is used to produce high-grade matcha and shaded teas. Many other cultivars are used to prepare relatively small amounts of tea. The tea that I’m focused on today, though, was mostly forgotten about outside its home region. Instead, it’s a misfit. It was considered unsuitable for large-scale production with a flavor profile that didn’t fit the standard palate of the 20th century. This cultivar is Shizu-7132, and its tea has the flavor of cherry blossoms. Shizu-7132 Back in the 1960s, researchers were trying to find a new cultivar that would supplant Yabukita as the go-to cultivar in tea production. They wanted more umami flavor, stronger aroma, and greater resistance to cold and disease. They didn’t rely on artificial breeding programs, though. Instead, they harvested seeds from Yabukita trees in local tea fields and planted them. Although several interesting varieties were found over the years, many had characteristics that made them less desirable in Japan’s highly mechanical tea production system. Shizu-7132 was one of those experimental cultivars. Its strong, cherry blossom-like aroma and flavor were unique, but its leaves also proved problematic during production. Typically, steamed tea leaves are shaped into needles using rolling machines. This step helps break down the leaves and release more flavor compounds. The thicker stems of Shizu-7132 didn’t play well with rolling machines designed for standard cultivars like Yabukita. The cultivar does have its mother’s strong resistance to frost and certain diseases, though. Researchers are uncertain what the father plant is. Some even speculate that the father was a foreign variety used to make black tea. This might explain where the “un-Japanese” flavor profile comes from. Despite all its positive characteristics, Shizu-7132 was never officially registered. It didn’t fit the mold of what was considered desirable at the time. Sidelined, it was mostly relegated to local tea fields in Shizuoka. We owe its continued existence to the work of local tea farmers in that region. What Makes it Special Teas made from Shizu-7132 contain coumarin just like fermented cherry blossoms. In fact, the coumarin i
