When talking about cream down, most tea lovers immediately think of black tea, for this phenomenon shows up most distinctly in black tea.
Freshly brewed black tea has a clear and bright liquor. Once cooled below 40℃, tiny flocculent substances will appear in the tea liquid, which is known as cream down, and those precipitates are called tea cream. For black tea, caffeine combines with large molecules including thearubigins, theaflavins and proteins through hydrogen bonds and hydrophobic interaction when temperature drops, forming tea cream. Among these substances, caffeine and theaflavins are the key factors creating cream down. Theaflavins are generated only during the fermentation of black tea. Other types of tea contain little or no theaflavins at all. That explains why cream down is a typical feature of black tea only.
The formation of cream down is also an important sign of high-quality black tea. It proves the tea is rich in internal substances. Especially the content of theaflavins is directly proportional to black tea quality.
2. Cream Down in Other Types of Tea Cream down is not exclusive to black tea. It also occurs in other tea categories, most notably in Yunnan large-leaf green tea and Guangdong oolong tea (Phoenix Dancong). Ester catechins can complex with caffeine, proteins and other macromolecular substances. Therefore, teas with high contents of tea polyphenols and caffeine are prone to cream down. Yunnan large-leaf green tea and Guangdong Phoenix Dancong oolong tea contain abundant tea polyphenols and caffeine. For this reason, these teas will also produce visible flocculent precipitation when the tea liquor cools down.
3. Impacts of Cream Down on Ready-to-Drink Tea and Industrial Solutions Although cream down indicates tea is rich in internal compounds and generally of superior quality, it becomes a huge problem for RTD (ready-to-drink) bottled tea. Cream down usually forms floccules inside liquid. When consumers spot flocculent sediment in bottled tea, they will immediately assume the drink has gone bad, as microbial spoilage also creates the same kind of suspended particles. Besides, beverage companies have long guided consumers to believe crystal-clear tea is better, making buyers extremely sensitive to any sediment in tea drinks.
Several processing methods are adopted to eliminate cream down: The most common practice is cooling and centrifugal filtration. Since low temperature triggers cream down, extracted tea liquor is chilled below 40℃ so that tea cream fully precipitates, then centrifuges separate these complexes out. If centrifugation cannot remove macromolecules completely, manufacturers will add an ultrafiltration process.
Ultrafiltration membranes trap theaflavins, thearubigins, proteins and other large molecules. Without these substances, tea cream can no longer form. However, this method comes with a cost: the more thoroughly macromolecules are removed, the lower the production yield, and the more original tea flavour is lost. For this reason, researchers developed an enzymatic treatment: adding tannase and protease to break large molecules down into small fragments. This technique is not widely used in tea production at present.
Enzymes are expensive, hydrolysis tends to alter tea colour and taste, and the whole process requires strict precise control over temperature and reaction time. Another approach is chemical solubilization. Strong alkalis such as sodium hydroxide or potassium hydroxide are added to break the bonds between tea polyphenols and caffeine, followed by centrifugation. This method works remarkably well against cream down. Yet alkali will darken tea liquor and ruin natural flavour, and lightly fermented teas suffer the worst flavour damage.
In 1990, Professor Yan Shouhe pointed out in his book Biochemistry of Instant Tea that producing cold-soluble high-aroma black tea would be a long-standing challenge for the instant tea industry. It is extremely difficult to eliminate cream down while preserving the original rich tea flavour.
