Is All Shade Created Equal?

Somehow, I've managed to get even geekier about tea this past week. Seriously, the abundance of tea-related research that is out there regularly amazes me. There are so many scientists spending so much time researching the minutiae of tea-growing. Today, we'll look at just a little sliver of that research as it relates to matcha. 

In a recent email I speculated about why our Wild Yabukita is so special, and wondered whether it had anything to do with the color spectrum of the shade that gets filtered through a forest canopy. If you need a refresher, this is a tea we have that has been grown in a forest, rather than a tea field, and the only shading it has received is that which naturally exists as a result of the trees growing overhead. It is also remarkably tasty, probably for many reasons - one of which is shade. 

Since that email, I've done some research. I'll share it here!  

Conventional Shading Techniques

There are a few different ways that modern tea plants are shaded, and they typically fall into two camps: high-shading and low-shading. High shading refers to canopies that have been built over the tea bushes. This often looks like black tarps held aloft on stilts, allowing workers to stand beneath them as they tend the plants. Low shading is when the tarps are draped over the bushes directly, and need to be peeled back any time the farmers want to access the plants. Both techniques can be used to make high-quality tea, but you often see people valuing high-shading a bit higher than low-shading. Often this is because having air flow around the tea bushes is seen as optimal, especially when it rains and water might otherwise get trapped between the tarp and the leaves. 

Almost always, however, these techniques use black tarps to block out the light. There are a few traditional farmers who created canopies of dried straw, but this is typical only for the highest-end, competition-grade teas. 

What if there's more to it?

The conversation about shading techniques typically ends there. However, it doesn't need to. The case of our Wild Yabukita suggests that there are other factors at play in determining the quality of shade, and one of those is the wavelengths of light that are blocked from reaching the tea plants. 

The ubiquitous black tarps uniformly block all wavelengths of light. It is typically blue and red wavelengths that are the drivers of photosynthesis, with other colors like near-infrared and green playing supporting roles. We are learning, however, that plants are very complex, and they do more with light than simply photosynthesize. For instance, exposure to red wavelengths of light has been found to make strawberries tastier and more resistant to certain infections. 

With this understanding, there has actually been some research into the effects of using different colored tarps to grow shaded tea. Researches in China grew tea plants under black, blue, yellow, and red tarps, with a control group that was unshaded. 

The unshaded tea, as predicted, had the highest levels of catechins. Catechins are a sort of natural sunscreen that form in tea leaves, so when a plant is shaded, there is no need for catechin development. Meanwhile, teas shaded under black tarps had the lowest levels of catechins. This is a willful trade-off: by foregoing catechins, shaded teas retain higher concentrations of savory amino acids, which normally would degrade with exposure to sunlight. 

By using colored tarps, however, the shade-grown tea plants were found to have higher concentrations of catechins while still retaining the distinct characteristics of shade-grown tea. The red tarps had the most pronounced effect, producing tea with more catechins than any of the other shaded teas (though still not quite as much as sun-grown tea). 

The red tarps had a particular effect on the color spectrum of the light getting through to the tea plants, shifting the wavelengths towards the redder end of things, with a higher proportion of wavelengths in the deep red and near-infrared end of the spectrum.

This is important, because vegetation - though it is green - produces similar changes to the color spectrum of the light that passes through it, with the addition of green wavelengths of light. So with this in mind, we can infer that tea grown under a forest canopy would likely have higher levels of catechins. 

Catechins, it should be noted, do not just provide health benefits. They have also been found to contribute to the aroma and flavor of tea, both directly and through their interaction with other compounds in the leaves.  Though some of them can be perceived as bitter, they can also contribute nutty and vegetal aromas that make a green tea taste "green." 

What's more, separate studies have found that exposure to red wavelengths of light can increase the expression of genes responsible for the creation of aromatic terpenes in tea. 

Finally, there is research indicating that the light that gets filtered through a forest canopy is highly variable depending on the biodiversity of the forest, with each tree type influencing the specific wavelengths that make it through. 

Ultimately, this doesn't prove anything definitive about what is going on with our Wild Yabukita, but it does suggest, yet again, that there is a complex interplay of many different factors at work in producing quality tea, and the color of the shade is certainly one of them. 

----------------------------------------------------------------------------------------------------

Alright, thanks for humoring me. I hope that was as interesting to you as it was to me! 

Thanks for reading and happy sipping,

Simon