A monitoring system using a piezoelectric sensor was developed for the quantitative analysis of the stirring process in which a mixture of a thickener with water was prepared. A thin piezoelectric sensor film was attached to the inside of a glass container in which the mixture was stirred and connected to a recorder. Seven healthy young participants were asked to conduct stirring for 90 s at three cycles per second (3 Hz). A triphasic wave with a large upward peak was recorded in each cycle of stirring. The average period across the seven participants was 0.337 s (n = 613 cycles), and statistical analysis revealed no significant difference between the average value and the expected value of 0.333 s. Video images captured during stirring were analyzed, and the analysis showed that the peak of the large upward wave appeared approximately 0.12 s (approximately 36% of the average period) after the time when the spoon head for stirring passed near the piezoelectric sensor. The monitoring system developed in this study allows the precise temporal analysis of stirring for the preparation of a mixture.