Effect of Stirring Time and Speed on the Foaming Property of Powdered Green Tea

Abstract

The effect was investigated of the time and speed of stirring on the foaming property of powdered green tea. The foam volume, expansion rate and degree of stability were measured under the following conditions; powdered green tea was stirred at the rate of 300,400,450 times per minute for 0.5,1.0,1.5,2.0,3.0,4.0 minutes. Another experiment was done to investigate how long was needed to produce foam by nine experienced practitioners of the tea ceremony.
Stirring at up to 400 times per minute produced an increasing amount of foam with increasing stirring speed, but less foam was foamed as the stirring speed was increased further to 450 times per minute. As the stirring speed was increased, the foam tended to become finer and less stable.
Stirring for up to 1.5 minutes produced an increasing amount of Foam with increasing stirring time, but over 1.5 minutes of stirring resulted in no change in the foaming characteristics.
The longer the tea was stirred, the finer and less stable the foam became.
Although there were differences between individual tea ceremony practitioner, the average stirring time was 23.3 seconds, the first 13.4 seoconds being at a higher stirring speed.
A high stirring speed was approximately 300∼350 times per minute as judged from the foam volume, foam rate and stirring period.