The principle of distinguishing melons by hearing is this: the structure of watermelons is divided into peel and pulp. During the ripening process of watermelon, the hardness and elastic modulus of the pericarp change, that is, the pericarp with ripe pulp is more elastic, and it will feel elastic when flapping. Under the action of cellulase, the cellulose in the pulp is degraded, the sugar content and structure of watermelon will also change, and the tapping sound will naturally be different.

This method actually has a high academic name: nondestructive quality inspection of agricultural products based on acoustic characteristics. In the matter of picking melons, it refers to tapping watermelons, collecting and analyzing sound signals, so as to find the correlation between sound signals and watermelon quality.

Researchers from Zhejiang University once published a paper on 1, which identified watermelons by listening to sounds. They developed a device to detect the sugar content of watermelon by using acoustic characteristics. By recording the acoustic characteristic parameters of the pendulum hitting the equator of watermelon, we found that the signal acoustic transmittance parameters had a good correlation with the sweetness of watermelon, with the highest value of 0.8842.

In addition, according to the experimental result 2 of the research team of Hebei Agricultural University, the vibration frequency of "raw" melons is greater than 189Hz, that of "cooked" melons is greater than 160- 189Hz, and that of "cooked" melons is greater than133-1. Translated into vernacular, it probably means that when you hit a watermelon and hear a sound like "click, click, click" on your forehead, congratulations, you have met a raw melon. If you hear the crisp sound of "knock, knock, knock" and feel the melon shaking, it means it is "cooked". When you hear the sound of "thump, thump, thump", which is similar to the sound of patting your chest, it means that the melon is ripe and sweet. When you hear the sound of "poof, poof, poof", it means that this melon is overcooked.