Many factors influence tea's taste, such as the time tea is harvested, the kind of teaware used, the water temperature, and the quality of the leaves. Intuitively, seasoned drinkers know a nice cup of tea. Scientifically, very few of us know just exactly why some tea tastes better than the other.
Today, I will talk about why tea tastes different based on the types of teawares, using scientific evidence.
For thousands of years, the Chinese have decided Yixing clay is superior in making tea, why is something puzzled people for generations. In 2017, 8 researchers experimented with comparing six types of teawares: Zisha (purple clay), Zhuni (red clay), stainless steel, ceramic, glass, and plastic.
To understand what makes tea taste different, let's first examine what's behind the scene.
Tea is rich in catechins - a type of phenolic compound ascribed a potent antioxidant activity.
There are four main types of compounds in tea catechins - EGCG, EGC, ECG, and EC. Although the names are similar enough and confused the heck out of me, each type contributes to tea's bitterness or astringency.
Other than catechins, tea also accumulates minerals such as aluminum, manganese, fluorine, and potassium, although much smaller in quantity.
Tea also contains volatile compounds, minimal in quantities, but play essential roles in taste.
All of those compounds contribute to the taste of tea. For example, caffeine makes tea taste bitter, while EGC contributes to the sweet aftertaste.
Yixing clay is made of kaolin, mica, and quartz and is rich in iron oxide. As you can guess, when mixed with hot water and tea leaves, Yixing clay was able to perform better than other types of teaware.
Upon examining the tea soup, researchers discover that tea brewed in Yixing clay (Zisha and Zhuni) has a higher amount of catechins, the lowest amount of caffeine (contribute to the bitterness). It also has a lower amount of volatile compounds and minerals (including heavy metal) compare to plastic, glass, stainless steel, and ceramic.
Although stainless teaware performed very similar to Yixing clay, it has a much lower amount of volatile compound than in Yixing clay tea soup. It is believed that the Yixing clay surface cavities allow water vapor and volatile compounds to pass through, which creates a pleasant aroma. In contrast, stainless steel's impermeable surface does the opposite.
The porosity of Yixing clay allows tea oil to pass through. Over time, the teapot becomes "seasoned," which creates an aromatic effect and upgrades the teapot's surface over time.
Heavy metal in minerals presents a minimal amount in tea soup, too small to be a concern. However, seasoned tea drinkers have at least one if not more cups of tea per day. Yixing clay has the lowest amount of mineral present; over time, it might make a difference. Potassium, which has an unpleasant heavy metal taste, also presents the lowest amount in Yixing clay.
Yixing clay teapots have been around for thousands of years. People at that time certainly don't have the technology we have today, but intuitively they decided that Yixing clay is superior in so many ways. I am grateful that we get to experience this beautiful piece of culture today.