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Tea and Terps · Episode 5
Nik and Travis brew a competition gyokuro, a green tea grown in shade, and follow the color of a leaf down to its molecules: chlorophyll, carotenoids and anthocyanins, and what each one means in a grow room.
The cup
Gyokuro is Japan's shade-grown green tea. For roughly the last three weeks before picking, the bushes are covered, and the leaf responds to the dimmer light by growing darker and richer in chlorophyll while it holds on to more of the amino acids, theanine above all, that taste savory and sweet.
Nik's cup is a competition production from Uji, near Kyoto, the region he calls the mecca of Japanese green tea, hand rolled by a sixteenth-generation master. Japanese green tea is made simply: the fresh leaves are steamed, rolled and dried. Steaming stops the browning before it can start, the way a sliced apple stays white if air never reaches it, so the cup keeps the leaf much as it grew.
What Nik noticed
Special notes
Shaded before harvest, then steamed, rolled and dried.
Gyokuro is brewed cool and slow. Water well below boiling keeps the umami in front, because hotter water pulls more of the bitter, astringent catechins. Nik also pours gently down the side of the pot, so the stream lifts the leaves instead of crushing them.
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Shade
For cannabis, Nik says, quality is built in strong light: the compounds a resin grower wants depend on high light intensity and a high energy load. Gyokuro is grown the opposite way: covering the bushes for the final weeks before picking is the central step of the method.
Under cover the leaf changes in several ways at once. It turns a deeper green and adds chlorophyll, it keeps more of its free amino acids, theanine above all, and it builds fewer of the catechins that taste bitter and astringent. The savory sweetness in the cup comes from that changed leaf, not from one molecule turning into another.
the compounds that we're looking to produce in these plants are a function of high light intensity and a high energy load.
Nik, on cannabis
| What changes | Grown in open sun | Covered before picking |
|---|---|---|
| Leaf color | Lighter green | More: Deeper, darker green |
| Chlorophyll | Less | More: More, with a larger share of chlorophyll b |
| Free amino acids, theanine above all | Fewer kept | More: More kept |
| Catechins | More | Less: Fewer |
| In the cup | Brisker and more astringent | Sweeter, rounder and more savory |
Directions of change measured in covered tea (Sano and colleagues, 2018; Sakaida and colleagues, 2010). How large each change is depends on the cultivar, the cover and its timing.
Chlorophyll
It is tempting to picture photosynthesis as sunlight landing on a green molecule and sugar coming out the other side. Nik's picture is closer to what happens. Chlorophyll sits in organized antennas, hundreds of pigments held at exact distances by proteins, like stars in a constellation. A photon excites one pigment, and the energy hops from neighbor to neighbor toward the center.
At the center sits the reaction center's special pair of chlorophyll a. When the energy arrives, an electron is pushed out and handed down a chain of carriers. Nik compares it to a lightning strike: charge builds, then discharges all at once into a ground downstream. That moment, charge separation, is where light becomes chemistry.
Shade changes the antenna. A shaded leaf builds a larger one, richer in chlorophyll b, so each reaction center collects energy from a wider area. Press Shade to see it.
your chlorophyll pigments are dotted like stars in a constellation
Nik
An illustration of the arrangement, not a molecular structure: each dot is a pigment. A real photosystem holds a few hundred chlorophylls for each reaction center.
Color
Chlorophyll absorbs strongly at both ends of the visible spectrum, in the blue and in the red, and least in the green, which is why leaves look green. Its two forms differ by a single small group of atoms, a methyl on chlorophyll a where chlorophyll b carries a formyl, and that is enough to shift the colors each one catches.
The other pigments fill in around it. Carotenoids absorb blue and blue-green light and pass some of that energy on to chlorophyll. Anthocyanins absorb green and yellow-green light, and they look red to purple to our eyes because the blue and red they leave behind is what comes back to us.
Simplified absorption of the purified pigments, each scaled to its own peak: chlorophyll a near 430 and 662 nanometers, chlorophyll b near 453 and 642, carotenoids between about 420 and 500, anthocyanins around 525. In a living leaf the bands broaden and shift a few nanometers. Press a pigment to see it alone.
Green light
Green is the color chlorophyll absorbs least, so it is easy to call it wasted, but the leaf still uses it. A green photon carries more energy than a red one; chlorophyll's structure just absorbs green less strongly. Hold a leaf up to the sun and the glow you see is green light passing through.
That leftover green is still put to use. Blue and red are mostly taken up in the first layers of cells, while green travels deeper into the leaf, where it still drives photosynthesis. In strong white light, measurements have found extra green light raising a leaf's photosynthesis more than extra red light does. As the hosts put it, the inside of a canopy, and even of a single leaf, is almost shade grown by itself.
A schematic cross-section, with qualitative depths: blue and red are absorbed near the upper surface, green reaches the spongy cells, and some passes through (after Terashima and colleagues, 2009).
Anthocyanins
Nik's favorite way to explain anthocyanins starts at a sandwich shop that builds from the middle out. The meat is the core: one of three, pelargonidin, cyanidin or delphinidin, which differ in how many hydroxyl groups they carry. Strawberries owe their red to pelargonidin; blackberries make cyanidin, and so, Nik notes, does cannabis.
The dressing is methyl groups, which turn those cores into peonidin, petunidin and malvidin and nudge the color as they go. The bread is sugar: attached to the core, it makes the pigment soluble in water, so it can move through the plant and dissolve in the cell's watery vacuole. Finally comes the wrapping, with a delivery slip, in Nik's telling, that sends each one where it belongs.
Acidity matters too. The same anthocyanin runs red in acid and shifts toward purple and blue as the pH climbs. It is at its most stable in acid; push the pH far enough the other way and it breaks down for good.
imagine walking into a sandwich shop and the first thing that they ask is, 'What kind of meat do you want?'
Nik
A typical anthocyanin in solution. In living tissue, metals and other molecules held alongside it shift the color as well.
Carotenoids
If anthocyanins are sandwiches, Nik says, carotenoids are cables. Every one starts as phytoene, a colorless chain of forty carbons. Enzymes add double bonds along it, and as the run of alternating bonds grows, the chain begins to absorb visible light: lycopene, the fully extended chain, is red. Close a ring at each end and you have the orange carotenes. Add oxygen and you have the yellow xanthophylls.
In the leaf they work as shock absorbers. They help harvest blue light, and they protect the machinery when the light is too strong. The xanthophylls even change form with the light: in strong sun, violaxanthin is converted, through antheraxanthin, into zeaxanthin, which helps the leaf shed the excess as heat, and in dim light the cycle runs back.
When carotenoids are cut, some of the pieces act as signals. The plant hormone abscisic acid, which helps close the stomata under stress, is cut from them. Episode 6 picks up the thread from there: the same kind of cutting gives beta-ionone, which smells of violets.
Carotenoids are like cables that are formed and there's 2 end caps
Nik
Strong light drives the cycle to the right; dim light runs it back.
Real structures
Five molecules from the episode, rendered from real PubChem geometry rather than drawn. Pick one to read why it matters, then turn it in three dimensions.
The pigment that catches light. Four nitrogen atoms hold a magnesium at the center of its ring, and a long tail anchors it in the membrane. Chlorophyll b differs by one small group, a formyl where chlorophyll a carries a methyl, which is enough to shift the colors it absorbs.
Structure data: PubChem open chemistry database
The orange carotenoid of carrots, and of every green leaf underneath its chlorophyll. A long chain of alternating double bonds absorbs blue light, and a ring at each end sets its shade of orange.
Structure data: PubChem open chemistry database
A cyanidin core with one sugar attached: the meat and the bread of Nik's sandwich. Cyanidin carries two neighboring hydroxyl groups on one ring, where pelargonidin has one. It is the main anthocyanin of aronia berries.
Structure data: PubChem open chemistry database
The amino acid behind gyokuro's savory taste, found almost nowhere outside tea. The tea plant makes it in its roots and sends it up to the leaves, and shade helps the leaf keep it.
Structure data: PubChem open chemistry database
One of the most abundant terpenes in cannabis, and the starting point of the hashishene question. Light and oxygen can keep rearranging terpenes like this one after harvest; what myrcene becomes depends on conditions that are still being worked out.
Structure data: PubChem open chemistry database
Drag to rotate. Scroll or use +/- to zoom.
In the grow
Travis brought an old piece of grow lore: feed plenty of nitrogen late in flower and some plants purple out. Nik explained why it does not hold up. Anthocyanins do start from an amino acid, phenylalanine, but the very first step of their pathway strips the nitrogen off. An enzyme called phenylalanine ammonia lyase keeps the carbon body and releases the nitrogen to be recycled, so none of it ends up in the purple pigment.
Chlorophyll is the opposite. Four nitrogen atoms sit in its ring, holding the magnesium at the center, and that nitrogen stays. Extra nitrogen late in flower can go into green chlorophyll but not into purple pigment, and Nik's warning is that it tends to bring stretch and leafy growth rather than color. Travis's usual suspects, genetics and a wider gap between day and night temperatures, are the better-known routes to purple.
you don't want to feed too much nitrogen too far into flowering. It's gonna mess with the flowers.
Nik
| Built from | Chlorophyll | Anthocyanin |
|---|---|---|
| Starting point | Glutamate, built up into a ring of four pyrroles | The amino acid phenylalanine |
| Nitrogen in the finished pigment | More: Four atoms, holding the magnesium | Less: None, removed at the first step |
| Its job | Catches light for photosynthesis | Screens light and buffers stress |
| Its color | Green | Red, purple or blue |
Moments worth rewinding
Moments from the clip archive. Each one plays the full episode from where it starts, and the short plays on its own.
Light and oxygen keep working on terpenes after harvest. A 2014 study proposed that light rearranges myrcene into hashishene in sun-dried material, though later tests did not find it under their own conditions.
The same terpene can attract one species and deter another. Nik's example is limonene, which is harsh on soft-bodied insects.
A top flower and a lower one from the same plant test differently for terpenes, while the cannabinoid molecules stay the same.
When strong light damages carotenoids, some of the fragments act as alarms, and the stress hormone abscisic acid is itself cut from carotenoids.
Anthocyanins absorb green and yellow light, and the blue and red they send back read as purple.
Purple pigment can climb a trichome's stalk and stop short of the head. One likely reason: anthocyanins dissolve in water, and the resin head is oily.
Cool nights raise anthocyanins in many plants, and Nik suggests that besides screening light they help cell membranes cope with the cold.
When the light drops, so does the water a plant moves. Nik tapers the light as the pot dries, not straight after a heavy watering.
Keep listening
Episode 5 continues where Episode 4 stopped, and Episode 6 follows the thread from pigment to aroma.
Episode 4 · The one beforeB Vitamins and BulangB vitamins as the cofactors that let a plant build its terpenes, pigments and cannabinoids.
Episode 6 · The one afterFlavors and Oriental BeautyOriental Beauty, a tea that needs insects to bite it, and the chemistry of what we smell.
Episode 1 · Where it beganCarbon and Fenghuang OolongCarbon, the element plants are built from, over a cup of Phoenix oolong.
