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Bubble Tea

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Originating from Chun Shui Tang teahouse in Taiwan in the 1980s, bubble tea has since exploded in popularity worldwide2. It was accidentally created by the teahouse’s product development manager, Ms. Lin Hui, who decided to pour tapioca balls into her Assam iced tea for fun2. Over twenty years later, bubble tea can be found on every Taiwan street, neighboring countries like Japan, South Korea, and China, and even in North America2. With great flexibility in flavors, the drink can have a unique twist depending on each maker’s style. In its simplest form, bubble tea is a combination of tea and milk sweetened with sugar and topped off with tapioca pearls7. The tapioca pearls are starchy circular bubbles that are sweetened with sugar or honey and consists of a chewy texture that pleasantly compliments the milky tea and gives the drink its unique trademark7.

The flavor and texture of the tea are created by the chemical reactions between the tea, milk, and sugar, and the bonds between the starch in the tapioca balls. The main varieties of tea used are oolong, green, or black tea4. These tea leaves all contain amino acids, the major amino acid being theanine, that are converted to polyphenols when exposed to the sun4. The slight bitter sensation people taste when consuming tea is attributed to polyphenols4. Major types of polyphenols include catechin, epicatechin, gallocatechin, and epigallocatechin4. The amount of sunshine the leaves get is directly correlated to the level of bitterness, with more sun making the tea more bitter due to higher levels of theanine converting to polyphenols10. The benzene ring structure of the polyphenol conversion absorbs light in the UV wavelength range, which protects the leaves from being scorched by the sun10.

When the tea is consumed with milk, the polyphenol reacts with the casein proteins in milk and salivary proteins in the mouth. This reaction forms soluble and insoluble complexes through hydrophobic interaction and hydrogen bonding9. These complexes lessen the amount of free polyphenols in the environment leading to less absorption of them into the oral membranes.9 Bubble tea also contains added sugar that boosts this process, since sugar and water molecules have a high affinity to covalently bond3. This leaves more space and higher chances for polyphenols to bump into casein proteins forming the complexes3. Additionally, sugar, which is composed of glucose and fructose heightens the sweet taste of the drink. Being monosaccharides, glucose and fructose can be quickly absorbed producing the sweet taste on the tongue5. All of these factors together lessen the overall ability to taste the bitterness of the tea. Finally, the chewy texture experienced as you munch on the tapioca pearl is attributed to the glycosidic linkages that result from the formation of starch1. Specifically, these are alpha linkages making the structure of starch very malleable while still easily digestible by the enzyme, amylase, that naturally exists in our saliva1. Although the pearls are made from starch, which is composed of repeating glucose subunits, they don’t taste sweet on their own5,6. This is due to starch being a polysaccharide. Unlike glucose and fructose, which are monosaccharides and can be easily absorbed in our mouth, starch needs a longer time to be completely broken down into its monosaccharide subunits5. By then, it is in the stomach and gut where the glucose will be absorbed directly into the bloodstream so one is unable to taste it5.

Now, try it for yourself! Here’s a simple recipe on how to make bubble tea.

  • ¾ cup of brewed tea (black, oolong, or green)
  • ½ cup of milk
  • ¼ cup of tapioca pearl
  1. Tapioca pearls are packaged dry to increase shelf life, but that makes the bubbles much too tough to be consumed directly. Submerge the tapioca pearl in water and boil for 15 minutes. During this process, the starch granules in the bubbles would absorb the liquid and gelatinize making it softer to chew and easier to digest.8 The boiled water would also gelatinize so the liquid must be discarded. Rinse the cooked pearls with warm or cool water to remove excess stickiness. To flavor the bubbles, add a tablespoon of sugar and mix the pearls evenly.
  2. Using a cocktail shaker, combine the tea, ice cubes, and milk. Add table sugar as needed into the mixture if you prefer a sweeter drink. Shake until the mixture becomes frothy. This process promotes contact between the polyphenols and caseins to increase complex formation which lessens the bitterness of the tea.
  3. Place the tapioca pearls into your favorite cup first then pour the mixture in.

Enjoy!

Resources:

  1. Berg J. M.; Tymoczko J.L.; Stryer L. Biochemistry 5th edition. Complex Carbohydrates Are Formed by Linkage of Monosaccharides. https://www.ncbi.nlm.nih.gov/books/NBK22396/ (accessed Oct 11, 2016)
  2. Chang, D. Is this the inventor of bubble tea. http://travel.cnn.com/explorations/drink/inventor-bubble-tea-885732/ (accessed Sep 28, 2016).
  3. Garner, D. Sugar in your cuppa… not just about a sweet tooth. University of York. https://www.york.ac.uk/news-and-events/news/2015/research/tea-coffee-sugar-chemistry/ (accessed Oct 11, 2016)
  4. Gebely, T. Chemical Compounds in Tea. World of Tea. https://www.worldoftea.org/tea-chemistry/ (accessed Sep 28, 2016)
  5. Hendrickson, K. Just Because It Isn’t Sweet … Doesn’t Mean It Isn’t Sugar. http://www.highlighthealth.com/food-and-nutrition/just-because-it-isnt-sweet-doesnt-mean-it-isnt-sugar/ (accessed Oct 25, 2016).
  6. Polymer Science Learning Center. Starch and Cellulose. http://www.pslc.ws/macrog/starlose.htm (accessed Sep 28, 2016).
  7. Tasty Chemistry: Key Components of Bubble Tea. http://iloveserenitea.com/bubble-tea-ingredients/ (accessed Sep 28, 2016).
  8. The Culinary Institute of America. Food Science Basics: Effects of Heat on Starches and Sugars. http://chefsblade.monster.com/training/articles/215-food-science-basics-effects-of-heat-on-starches-and-sugars (accessed Oct 25, 2016).
  9. Yan, Y.; Hu, J.; Yao, P. Effects of Casein, Ovalbumin, and Dextran on the Astringency of Tea Polyphenols Determined by Quartz Cry. Am. Chem. Soc. [Online] 2009, 25, 397-402.
  10. Zen, K. Secrets of Tea Seasons and Ageing. http://www.kyarazen.com/secrets-tea-seasons-aging/ (accessed Oct 25, 2016).