A Smarter Way to Make Tea? Optimizing Brewing Conditions of Oolong Tea Using Quadratic Orthogonal Regression Design

Zhifei Zeng ’23

Figure 1: A Chinese research team used a mathematical model to derive the optimal brewing conditions for oolong tea.

Tea culture is one of the traditional cultures in China, and because of the variety and long history of Chinese tea, the brewing process varies from person to person. During the brewing process, tea leaves release flavorful substances. The main factors that affect the flavor and health benefits of the tea include the choice of water, water-to-tea ratio, brewing temperature, and time. A research team from China recently used a quadratic orthogonal regression design, a method of multivariate statistical analysis, to derive optimal brewing conditions for an oolong tea called Tieguanyin.

The researchers used pure water to brew Tieguanyin Oolong tea and applied a brewing method with three consecutive extracts to simulate daily tea drinking. The researchers prepared a total of three tea infusions by adjusting the brewing time to simulate different brewing conditions. Consumers with varying tea drinking habits were then invited to rate the sensory preferences of these tea infusions, while five trained members rated the floral fragrance, bitterness-astringency, and overall flavor of the tea. In addition, the researchers analyzed the color, chemical composition, and antioxidant activity of each tea infusion. Finally, the researchers proposed a mathematical model based on a quadratic orthogonal regression design to calculate the best brewing solution to meet the needs of different consumers. The results showed that a higher water-to-tea ratio or lower temperature resulted in tea infusions with less bitterness-astringency, increased bioactive compounds and antioxidant activity, and a lighter color. Occasional tea drinkers preferred teas with less bitterness, while the opposite was true for everyday tea drinkers. Occasional tea drinkers showed no significant preference. The researchers also found that a polyphenol called catechin was the main contributor to the antioxidant capacity of the tea and that higher temperatures or lower water-to-tea ratios increased the antioxidant capacity of the tea.

The study suggested the most suitable brewing conditions for oolong tea for groups with different tea-drinking habits. The researchers analyzed not only the sensory results, but also the chemical composition and antioxidant capacity of the tea, and used mathematical models to find the optimal brewing conditions. The study reminds us that even tea brewing can be done in a scientific way to get the optimal brewing conditions, resulting in a better-tasting and healthier tea.

Works Cited:

[1] QQ. Cao, et al., Optimization of brewing conditions for Tieguanyin oolong tea by quadratic orthogonal regression design. npj Sci Food 6, (2022). doi: /10.1038/s41538-022-00141-7

[2] Image retrieved from: https://get.pxhere.com/photo/liquid-tea-teapot-cup-food-brown-beverage-drink-black-lifestyle-teacup-relaxation-hot-organic-775498.jpg


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