How to tell if a watermelon is unsafe to eat?

January 9, 2026 •

4 min read

According to the U.S. Department of Agriculture (USDA), whole watermelons have a shelf life of up to 10 days at room temperature, while cut watermelon can last up to 5 days when properly refrigerated. However, these are just guidelines, and spoilage can occur faster. Knowing the specific indicators of an unsafe watermelon is crucial for preventing foodborne illness.

Quick Summary

Identify spoiled watermelon by checking for sour smells, slimy or fuzzy textures, mold, and off-tasting or fizzy sensations. Discard any melon showing these signs to avoid food poisoning. Proper storage is key to extending freshness.

Key Points

Check for Mold: Any visible mold, fuzzy spots, or dark, discolored patches on the rind or flesh indicates spoilage.
Trust Your Nose: A sour, tangy, or fermented smell is a definitive sign that a watermelon is bad and should be discarded.
Beware of Slimy Texture: If the flesh feels slimy or slick to the touch, it is unsafe to eat due to bacterial growth.
Listen to the 'Thump Test': A dull, thud-like sound instead of a hollow one can mean the melon is overripe or rotten inside.
Look for Foaming: Any bubbling or foaming in the cracks of a cut melon signifies fermentation and makes it unsafe to consume.
Mind the Storage Time: Cut watermelon should be refrigerated promptly and consumed within 3-5 days; whole melons last about 1-2 weeks depending on storage conditions.
Avoid Fizzy or Sour Taste: If you taste a small piece and it has a fizzy or sour flavor, spit it out and throw the rest away.

A juicy, sweet watermelon is a summer staple, but a spoiled one can pose a health risk due to bacterial growth. Eating bad watermelon can lead to food poisoning symptoms like nausea, vomiting, and diarrhea. Fortunately, several clear signs can help you determine if your watermelon is unsafe to eat before you take a bite.

Visual and Olfactory Cues: What to Look For and Smell

Signs on a Whole Watermelon

Even before you cut into it, a whole watermelon can give off warning signals. Look for mold, which may appear as fuzzy white, green, or black spots on the rind. The rind itself should be dull, not shiny, and feel firm to the touch. Soft or mushy spots, as well as large dents, are indications of internal decay. Another crucial check is the 'field spot,' the yellow patch where the melon rested on the ground. A creamy or buttery yellow spot is good, but a dark brown or black field spot can signal spoilage. A melon that feels surprisingly light for its size may also have lost its moisture content and is likely past its prime. Lastly, give the base of the melon a sniff; a fermented, sour, or tangy smell coming through the thick rind is a strong indicator of an unsafe melon.

Signs on a Cut Watermelon

Once a watermelon is cut, its shelf life decreases dramatically. It should be refrigerated in an airtight container and consumed within 3 to 5 days. Signs of spoilage on a cut melon are often more obvious:

Visible Mold: Mold spots are easier to see on the exposed red or pink flesh. Discard the melon immediately if you see any.
Color Changes: The vibrant flesh may become dull, faded, or milky in color. Dark, brownish patches within the flesh also indicate rot.
Slime: A slimy or wet texture is a clear sign that bacteria are present and the melon is unsafe to eat. Do not attempt to rinse it off.
Foaming: Bubbling or foaming around the cut surfaces means the fruit's sugars are fermenting, caused by bacteria. Throw it out if you notice this.
Texture and Taste: A mealy, grainy, or mushy texture is unpleasant but may still be safe, though the flavor will be diminished. However, a sour or fizzy taste means it's fermenting and should be discarded.

Safe Handling and Storage Practices

Proper handling is critical for preventing contamination. Before cutting any melon, thoroughly wash the outside rind under cool, running water using a produce brush. This removes any surface bacteria that could transfer to the edible flesh. After cutting, store any uneaten portions in the refrigerator at or below 41°F (5°C). Keeping cut melon in an airtight container helps preserve freshness and prevents odor absorption. The USDA also warns against storing cut watermelon at room temperature for more than two hours.

Comparison Table: Safe vs. Spoiled Watermelon


Feature	Safe Watermelon	Unsafe Watermelon
Appearance	Dull, firm rind with a creamy yellow field spot. Vibrant red or pink, smooth flesh.	Soft spots, dark patches, or visible mold on the rind. Discolored, faded, or dark flesh.
Smell	Fresh, sweet aroma, especially near the base.	Sour, tangy, or alcoholic smell. Foul odor.
Texture	Firm rind. Crisp, juicy flesh (or mealy if overripe, but not rotten).	Mushy, slimy, or fuzzy rind. Slimy, mushy, or stringy flesh.
Sound (Thump Test)	Deep, hollow sound.	Dull or muffled sound.
Internal Signs	Uniform color and texture.	Foaming, cracks around seeds, or excessive liquid pooling.
Taste	Sweet and fruity.	Sour or fizzy sensation on the tongue.

Can overripe watermelon still be used?

Overripe watermelon, which is not yet spoiled, can still be used for certain recipes. For example, a slightly mealy watermelon is fine for making smoothies, juice, or even a sorbet where the texture will be transformed. However, if any signs of actual spoilage are present, it must be discarded completely. Trust your senses: if it looks or smells wrong, it's best to throw it out to avoid potential health risks.

Conclusion

Knowing how to tell if a watermelon is unsafe to eat is a key food safety skill. By paying attention to the melon's appearance, smell, and texture, you can protect yourself and your family from foodborne illness. Remember to inspect both the exterior rind and the interior flesh, and always practice proper storage techniques by refrigerating cut melon in an airtight container. When in doubt, it is always best to err on the side of caution and discard the fruit. A little diligence can ensure your summer treat remains a delicious and safe one.

A Note on Contamination

It is important to remember that bacteria can be present on the rind of a watermelon and transfer to the edible flesh when it is cut. Washing the rind thoroughly before cutting is essential to prevent this. For comprehensive information on food safety, including best practices for handling produce, consult reliable sources such as the USDA or your local food safety authority.

Food safety tips for melons from Canada.ca

Frequently Asked Questions

No, a soft or mushy spot on a watermelon, especially on the rind, is a sign of decay. It indicates that the fruit inside is likely overripe and potentially spoiled.

A bad watermelon smells sour, tangy, or like alcohol. A fresh watermelon should have a lightly sweet scent, especially near the stem.

An overripe watermelon that is mealy or grainy but lacks other signs of spoilage (mold, slimy texture, sour smell) is generally safe to eat, though less appealing. However, if any signs of rot are present, it is not safe.

Yes, eating rotten or spoiled watermelon can cause food poisoning, leading to symptoms such as nausea, vomiting, diarrhea, and stomach cramps.

Cut watermelon should be stored in an airtight container in the refrigerator and is best consumed within 3 to 5 days.

Foaming indicates fermentation, which is caused by bacteria breaking down the fruit's sugars. It is a clear sign that the watermelon is spoiled and unsafe to eat.

Yes, it is very important to wash the outside of the watermelon under cool, running water and scrub it with a produce brush before cutting. This prevents bacteria on the rind from transferring to the edible flesh.