How to Tell If Food Has Gone Bad

How to Tell If Food Has Gone Bad

Knowing when food has gone bad is one of the most practical food safety skills you can have. The challenge is that spoilage and safety are not always the same thing — some food looks and smells fine but is dangerous, while other food looks unappetizing but is perfectly safe. Here's how to navigate it.

Spoilage vs. Food Safety: The Key Distinction

• Spoilage bacteria cause food to look, smell, or taste bad. They're generally not dangerous — your senses will warn you before you eat enough to get sick.
• Pathogenic bacteria (Salmonella, E. coli, Listeria, Campylobacter) cause foodborne illness. They often produce no visible, smell, or taste changes. Food can look and smell perfectly fine and still be dangerous.

This is why "when in doubt, throw it out" is the correct rule — you cannot always rely on your senses.

Signs Food Has Gone Bad by Category

Meat and Poultry

• Sour, ammonia-like, or off smell
• Slimy or tacky texture on the surface
• Gray or green discoloration (note: some color change in beef is normal oxidation, not spoilage)
• Beyond safe storage time (raw poultry: 1–2 days; raw beef: 3–5 days; cooked meat: 3–4 days)

Fish and Seafood

• Strong "fishy" or ammonia smell (fresh fish should smell mild and oceanic)
• Slimy texture
• Dull, sunken eyes in whole fish
• Flesh that doesn't spring back when pressed

Dairy

• Milk: sour smell, curdled texture
• Cheese: mold beyond the rind (soft cheeses should be discarded entirely if moldy; hard cheeses can have mold cut off with 1-inch margin)
• Yogurt: excessive liquid separation, off smell, mold
• Butter: rancid smell

Eggs

The float test: place an egg in a bowl of cold water. Fresh eggs sink and lay flat. Older eggs stand upright. Floating eggs should be discarded. Cracked eggs should be used immediately or discarded.

Produce

• Mold (discard soft produce entirely; firm produce can have mold cut off with a generous margin)
• Slimy texture in leafy greens
• Fermented or off smell
• Significant discoloration beyond surface browning

Cooked Leftovers

• Beyond 3–4 days in the refrigerator — discard regardless of appearance
• Any mold growth
• Off smell
• Slimy texture

The Expiration Date Question

• "Best by" / "Best before": Quality date, not safety date. Food is often safe after this date but may have diminished quality.
• "Use by": Safety date for perishables — don't consume after this date.
• "Sell by": For retailers, not consumers. Food is typically safe for several days after the sell-by date if stored properly.

When to Always Discard

• Any food beyond its "use by" date
• Any food that has been in the temperature danger zone (40°F–140°F) for more than 2 hours
• Any canned food with a bulging lid, rust, or dents along the seam
• Any food with visible mold that is soft or liquid
• Cooked food beyond 3–4 days in the refrigerator

Use a digital food thermometer to verify that reheated food reaches 165°F — proper reheating kills most bacteria in food that has been stored correctly.