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應用研究影響案例 12



Ultrasound Milk Tea Machine

Dr Anna Cheung and Dr Emily Choi, Faculty of Science and Technology


Anna 1

TC-80 Milk Tea Machine


In China, Hong Kong style milk tea is popular primarily in the southern and middle parts of the country owing to its astringency, a bitter taste not easily accepted by everyone. At present, there is no brewing method available to control the astringency content of milk tea. If astringency can be controlled by machine, the taste of milk tea can be improved to cater for the drinking habits in different places.



Ultrasound-assisted extraction of tea leaves


Conventional tea brewing involves the soaking of tea leaves in hot boiling water at a temperature near 100°C, a method known as "Hot Water Extraction" (HWE). This diffusion method takes a long time and requires high heat energy consumption, hence it is unfavourable for industrial application. To produce Hong Kong style milk tea with higher efficiency and improved taste, a new kind of milk tea machine is needed.



Milk tea tasting trial findings


Dr Anna Cheung, Dr Emily Choi and their team explored another form of extraction mechanism called "Ultrasound-assisted Extraction" (UAE) to brew tea. This method enhances the extraction of tea leaves by using the mechanical force of sound waves. UAE only takes half the amount of time used in HWE and requires water temperature of about 40-50°C. UAE can also control the concentration of flavanols (also referred to as tannins), components whose reaction in boiling water determines the astringency aftertaste of tea. With the application of UAE, the astringency level of Hong Kong style milk tea can be controlled. Respondents to a sample tasting trial reflected that milk tea produced by combining the extraction methods of HWE and UAE tasted better as the tea had a smoother texture and less bitterness.