Effects Of Brewing Water On The Components Dissolution And Infusion Quality Of White Tea

In this paper, white teas were chosen as test materials for investigation of components dissolution, physicochemical properties and sensory quality of the tea infusion when different types of brewing water were applied, and the results were as follows:1.The physicochemical properties of 8 kinds of brewing water including mineral water(K1 & K2), pure water(C1 & C2), private water(ZY1 & ZY2), tab water(J) and distilled water(S) were analyzed, and shown as the followings:(1) The above water samples ranged from 6.41 to 7.03 in the pH value, when heated to temperature of 100C°and cooling down to room temperature, the pH values tested ranged from 6.32 to 7.44, indicating the poor thermostability of the pH values, especially the water samples C2 and S; (2) The above water samples ranged between 1.88-102.4μS/cm in the electrical conductivity, when heated to temperature of 100C°and cooling down to room temperature, conductivity tested ranged between 2.32～108.35μS/cm, indicating the poor thermostability of the conductivity especially the water samples K1 and J; (3) There were higher but variable contents of potassium, sodium, calcium, magnesium, chloride, metasilicic acid in the 8 samples, and potassium, sodium, magnesium and metasilicate revealed better thermostability in contents when water samples heated.2. The influence of the brewing water on the physicochemical properties of tea infusion was concluded as follows:(1) Tea infusion pH values of Fu’an Dabai and Zhenghe Dabai were negatively correlated with the brewing water pH values, with an increasing significance in the negative correlation when the tea grade decreasing; (2) The electrical conductivity between the above two infusions and the brewing water was positively correlated, the conductivity of Zhenghe Dabai infusion was more significantly correlated with that of the water; (3) With pH value increasing from 5.5 to 7.0, the above two infusions appeared from slightly dark yellow to bright apricot-yellow; (4)When higher values in lightness, hue and color difference, the above two infusions of better grades revealed a worse appearance in general, but infusions of lower grades appeared better in color; (5) Tea of different grades could be brewed into appropriate infusion color when water sample Kl applied and compared with the other 7 water samples, and Kl was tested as follows:pH6.63, conductivity 64.9 μS/cm,1.23 mg/L potassium,3.28 mg/L sodium,11.7 mg/L calcium,1.48 mg/L magnesium.3. The influence of the brewing water on components dissolution, taste of tea infusion was concluded as follows:(1) The quantities of water extract, polyphenols and free amino acids in tea infusion were significantly influenced by the water quality, when brewed in the different water the difference of contents of the above 3 components in tea infusion of Zhenghe Dabai was 62.54 mg/150mL,50.99 mg/150mL,18.94 mg/150mL respectively when maximum and minimum contents of each component were compaered, and as to Fu’an Dabai the difference was 99.78 mg/150mL,85.57 mg/150mL,17.72 mg/150mL respectively; (2) For higher grade tea, an appropriately higher concentration of magnesium ion contributed to the leaching of flavone glycoside; (3) The total amount between the water extract and the total amount of mineral ion, conductivity of the brewing water were positively correlated in inignificant or extremely significant level.4. The adjusting of the water pH value and its influence on the components dissolution and the flavor of infusion were investigated as follows:(1) Brewing water of the varied pH value contributed to difference of its electrical conductivity, its value of L, a, b,-a/b, E or their combination, thus leading to difference in the infusion color, in this experiment, the best infusion color appeared when tea was brewed with pH7 water; (2) Brewing water of the varied pH value led to difference in content of components of the infusion, and finally the flavor of the infusion; (3) Brewing water of lower pH value tend to produce lower amounts of free amino acids but higher amounts of polyphenols, correspondingly higher ratio of phenol/ammonia of the infusion, thus reducing the refreshing taste of infusion. In this experiment, the better taste was brewed by water of pH6 and pH7.5. The addition of mineral ions in water and its influence on the infusion flavor were investigated as follows:(1) With increasing concentration of potassium ion the infusion appeared dull in color in the process:shallow apricot yellow-apricot yellow-deep apricot yellow-orange, correlation analysis showed that infusion color was affected through the change of L value by potassium ion, and infusion of more potassium ions contributed to a salty taste; (2) Sodium ion showed similar effect to that of potassium ion, on infusion color by affecting the values of E and -a/b; (3) With increasing concentration of calcium ion, the infusion appeared turbid and dull in color which was described as the process of shallow apricot yellow-apricot yellow bright-apricot yellow-deep apricot yellow-dark orange-turbid, also in that process the infusion gradually reduced in dissolved flavor substances. In this experiment, the better taste was brewed by water with calcium ion concentration ranging 0-15mg/L; (4) Magnesium ion showed similar effect to that of calcium ion on infusion color, with its concentration increasing, the changing of infusion color was expressed as shallow apricot yellow-apricot yellow bright-apricot yellow-deep apricot yellow-dark orange-dull and in that process, infusion initially increased and then decreased in dissolved flavor substances. In this experiment, the better taste was brewed by water with calcium ion concentration ranging 0-15mg/L.