Introduction

Let's start with a strict definition:

Tea is a beverage made by steeping the leaves of the Camellia sinensis plant in hot water.

Like when I talked about meat, this definition bothers me. Let's expand it.

Water temperature

Do we have to steep the leaves in hot water? Instinctually, you might say we have to use boiling water. However, people often advise using less-than-boiling water for high quality green tea, e.g. 80 degrees Celsius or lower for matcha. In fact, “a few tea masters in Japan [even] suggest that the optimal way to prepare matcha is with cool water” to maximize the umami.

As a thought experiment, let's say you steep some tea leaves in hot water, then let it cool to room temperature. Then you steep the same amount of the same tea leaves in room temperature water. How do these differ? When you steep tea leaves, water soluble compounds from the leaves diffuse into the water. Hotter water molecules move more, so hotter water increases the rate of diffusion, creating a stronger tea. Since diffusion represents a physical, not chemical, change, though, the compounds stay the same.

So really, I don't think the temperature of the water forms a meaningful boundary of the definition of tea:

Tea is a beverage made by steeping the leaves of the Camellia sinensis plant in water.

Plant leaves

Can we include other plants? I certainly think so, given two examples:

1. Moroccan mint tea, which mixes mint leaves with green tea leaves
2. Masala chai, which mixes spices (and often milk) with black tea leaves

If you consider these two as tea, then the defintion of tea allows including other plants.

Tea is a beverage made by steeping the leaves of the Camellia sinensis plant (possibly mixed with other ingredients, often other plants) in water.

Camellia sinensis

Let's get ridiculous. Can we omit the Camellia sinensis plant?

Some setup: in the study of sensation and perception, the difference threshold represents the smallest change in a stimulus detectable at least half of the time. We can also call this the “just-noticeable difference” (JND).

Let's imagine a simple green tea. We can separate this into two parts: the water and the tea compounds. I remove (1% of your JND)‘s worth of tea compounds, which you cannot reliably detect. I keep doing this until you cannot distinguish the beverage from water. At no point could you reliably distinguish the beverage before and after, and at the end we have just plain water. So can we say “tea is water, possibly mixed with other ingredients”?

Hopefully that seems as nonsensical to you as it does to me. Coffee and canned sardine juice fall under that definition! Going back to the study of sensation and perception, the absolute threshold represents the lowest level of a stimulus detectable at least half of the time. So we can use the absolute threshold as a good boundary of definition:

Tea is a beverage made by steeping (a perceptible level of) the leaves of the Camellia sinensis plant (possibly mixed with other ingredients, often other plants) in water.

Tisane

What about herbal “teas,” like chamomile, which lack Camellia sinensis? If we omit Camellia sinensis, we get the same problem as before, so more properly we categorize these beverages as “tisanes."¹

Conclusion

I find myself pleasantly surprised at the breadth of science included in this more thorough definition of tea. At the same time, I find myself wondering what purpose this definition serves (and more broadly, why we define and use words, though I don't want to get into that right now). Like I did with meat, I'm leaving room for subjectivity in defining a food and drink term. How would you define tea? How does it differ from my definition, and why?