Can tapping a watermelon and listening to the sound really help distinguish its sweetness? Is this long-standing "folk secret" reliable? Today, we consulted an experienced old watermelon farmer with 30 years of experience, who not only revealed the truth about tapping watermelons but also shared three key tips for identifying watermelons by sound, helping you solve the problem of choosing watermelons!

1. The Scientific Basis of Tapping Watermelons: The Secret of Sound and Watermelon Ripeness

Tapping a watermelon and listening to the sound may seem simple, but it actually contains certain scientific principles. Old farmer Li told us that the sound of a watermelon is closely related to its internal structure and ripeness. During the growth process, the ratio of flesh to juice in the watermelon changes continuously, and these changes directly affect the sound produced when the watermelon is tapped.

1. The Physical Principles of Sound

When you tap a watermelon, the force of your palm causes vibrations inside the watermelon. These vibrations propagate through the flesh, juice, and cavities, ultimately forming the sound we hear. A ripe watermelon has firm flesh and abundant juice, allowing vibrations to propagate evenly, resulting in a deep and crisp sound. In contrast, an unripe watermelon has harder flesh and less juice, which obstructs vibration propagation, making the sound sharp or dull.

2. The Correspondence Between Ripeness and Sound

A ripe watermelon has sufficient internal moisture and soft flesh, producing a low "buzz" or "thump" sound when tapped, similar to tapping a water-filled balloon. An overripe watermelon may have too large internal cavities, resulting in a hollow sound, or even a somewhat "scattered" sound. As for an unripe watermelon, the sound is high-pitched, like tapping on hard wood.

2. The Old Farmer's Exclusive Tips: Three Key Tricks for Identifying Watermelons by Sound

Tip 1: Master the Correct Tapping Technique and Find the "Resonance Point"

Tapping a watermelon is not just about randomly hitting it a couple of times; the technique and position of tapping are crucial. Grandpa Li said that the "resonance point" of a watermelon is usually located in the middle of the fruit, near the stem or the blossom end. This is the area where the internal structure of the watermelon is most uniform, and tapping here can best reflect the state of the flesh.

• Correct Technique: Use your finger joints or palm to gently tap, with moderate force, similar to the sound of knocking on a door. After tapping, quickly bring your ear close to the surface of the watermelon and listen carefully for the echo.
• Incorrect Demonstration: Many people like to hit hard with their fingertips or punch it forcefully, which not only fails to produce a clear sound but may also damage the watermelon’s skin.
• Judgment Criteria: A good watermelon should produce a low, crisp, resonant "thump" sound. If the sound is sharp or lacks echo, it is likely an unripe watermelon; if the sound is hollow, it may be overripe or hollow inside.

Suggestion: Tap the watermelon several times and compare sounds from different positions to ensure accurate judgment. After all, a watermelon may produce slightly different sounds in different areas due to uneven internal structure.

Tip 2: Combine Appearance Features; Sound is Just an Aid

While listening to the sound of a watermelon is important, it should not be solely relied upon. Appearance features are also key to judging the quality of a watermelon. Grandpa Li shared several simple and memorable observation points:

• Look at the Stripes: The stripes of a ripe watermelon are usually clear, symmetrical, deep green, and shiny. Even spacing between stripes and a yellowish base color indicate that the watermelon has fully ripened on the vine.
• Feel the Skin: A good watermelon has a smooth and hard skin, and gently scraping with a fingernail should not leave obvious marks. If the skin is too shiny or soft, it may be unripe or have been stored too long.
• Weigh It: Among watermelons of the same size, a ripe watermelon has more moisture and is relatively lighter. When you pick it up and gently shake it, if you can feel a slight "water sound," it indicates sufficient juice.
• Check the Stem: A watermelon with a withered and slightly inward-curving stem usually has a higher ripeness. If the stem is still green, it indicates that the watermelon may have been picked too early.

Suggestion: Listening to the sound of a watermelon is just "the icing on the cake"; it must be combined with appearance features for a comprehensive judgment. For example, a watermelon that sounds crisp but has blurry stripes and a green stem is likely an unripe watermelon that is "all show and no substance."

Tip 3: Understand Variety Differences and Adapt to the "Watermelon"

There are many varieties of watermelons, and different varieties have different ripening characteristics and sound performances. Blindly applying the "tap and listen" method may lead to misjudgment. Watermelon selection tips:

• Qilin Watermelon: This type has a thin skin and delicate flesh, producing a crisp sound with a slight "ding" metallic quality when tapped. When selecting Qilin watermelons, prioritize those with smaller bodies and dense stripes.
• Black Beauty: Black Beauty watermelons have thick skin and firm flesh, producing a low sound close to a "buzz" when tapped. Pay attention to whether the body is uniform; those with smaller blossom ends are often sweeter.
• 8424 Watermelon: Known for its high sweetness, the sound when tapped is between crisp and low, resembling a "thump" with a hint of "ding." When selecting 8424, prioritize those with alternating yellow and green stripes and slightly shriveled stems.

Suggestion: Before buying a watermelon, you can ask the vendor about the variety, and then adjust your judgment criteria based on the characteristics of that variety. This not only increases the success rate of selecting watermelons but also helps avoid being "fooled."

3. Common Misconceptions: The "Pits" of Tapping Watermelons

Although tapping a watermelon and listening to the sound has some rationale, many people easily fall into misconceptions during practice, leading to selecting "mute watermelons" or "watery watermelons." Grandpa Li summarized several common issues to help you avoid pitfalls:

• Overly Trusting the Sound: Some people only listen to the sound, ignoring appearance and weight, resulting in selecting watermelons that look good but taste average. Sound is just a reference; comprehensive judgment is key.
• Using Excessive Force: Tapping a watermelon too hard not only prevents you from hearing a clear sound but may also crack the flesh, affecting the taste. A gentle tap is sufficient; treat your watermelon with care.
• Ignoring Environmental Interference: In a bustling market, background noise can interfere with sound perception. It is recommended to tap watermelons in a quieter environment or slightly cover your ears with your palms to enhance auditory sensitivity.
• Blindly Pursuing Large Watermelons: While large watermelons may look tempting, their ripeness may not be as uniform as that of medium or small watermelons. Watermelons with high sweetness are usually of moderate size, ideally weighing between 4-6 kilograms.