the 5 tastes of tea - what is bitter

What is Bitterness and Astringency?

Today on the podcast is a look into the science behind the bitterness in tea. Why do we taste it and how does it relate to tea? The five tastes: bitter, umami, sweet, sour, salt are only slightly understood, with many ambiguities still existing. Certainly, many foods will offer a mixture of these five tastes, but what about tea? What can tea offer to teach us about bitterness? What is really happening in our mouth when we taste bitter? This podcast seeks to explain just that. 

Show Notes


  • World Tea Podcast
  • Taste Podcasts
  • What I hope to achieve

Subjectivity vs. group consensus. The quality of a tea is defined by its taste experience. This changes as one becomes more aware of the history behind tea. Thousands of years of history and people drinking have given rise to expectations and criteria as to what a tea should be and this comes from taste, but taste itself is subjective, your genetic makeup determines how you experience taste, and therefore tea.

What is Taste/Aroma/Flavour?

  • Taste Defined
    •  Bitterness
    • Sour
    • Sweet
    • Salt
    • Umami
    • Metallic?
  • Aroma Defined
  • Flavour Defined

Today we are talking Bitterness and Astringency

  • What is Bitterness
  • What is Astringency
    • A Tactile Sensation, a touch sensation
    • Pucker, dry, sandpaper, rough, dry (RE: Astringent sub-qualities)
  • Areas of the tongue is a myth
  • What is actually happening on the tongue (Bitterness)?
  • Papillae
    • Taste buds
    • Gustatory Cells
    • Nerves
  •  Bitter Taste receptors – result of TAS2R genes. A 2011 study reported that catechins in tea active the TAS2R39 receptor. At least 25 different TAS2R recptors exists, each detecting a different compound.
  • What is actually happening on the tongue (Astringency)?

Affects the entire mouth

  • Compounds such as polyphenols which bind to proteins in salva causing them to contract and shrink.
  • Protein affected are proline-rich proteins and histatines. These salvitory proteins have a strong affinity towards condensed tannins

What Causes Bitterness and Astringency in tea?

  • Polyphenols
  • Is a chain or group of phenols
  •  A phenol is an organic compound characterized by a hydroxyl (-OH) group attached to a carbon atom that is part of a benzene ring. The simplest member being monohydroxybenzene/ carbolic acid
  • Both the types of polyphenol and its size affect how bitter it can be
  • The types of polyphenols in tea are a subset calleds flava-3-ol monomers
  • Catechin, epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate are the primary source of bitterness and astringency.
  • In oxidized teas, catechins become oligomers (dimmers) of Thearubigans and theaflavins which inclued tannins. These result in the change in liquor colour. Same antioxidant properties
  • Monomers are more bitter than astringent, while dimmers are more astringent than bitter.
  • They are astringent at lower concentrations and bitter at higher concentrations.
  • Interestingly enough a 1992 and 2004 study found that theflavins in black tea did not induced astringency. It was instead Quercetin-3-o-rutinoside. But what astringent feel they did contribute was described as pucker and rough.
  • There is no Tannic Acid in tea, but there are tannins as they are a type of polyphenol, specifically polymers of polyhydroxyflavan-3-ol monomer units.....or Catechins

A note on Chinese Terminology

  • Ku Wei
    • Lingering bitterness
    • Bitterness to astringency
    • Bitterness to sweetness