How can you tell if pesto has gone bad?

Look for: Black on top is oxidation (normal); Mold; Sour smell. When in doubt, throw it out — food poisoning is rarely worth the savings.

Can you eat pesto past its expiration date?

"Best by" and "use by" dates indicate quality, not safety. Pesto can usually be eaten 1–7 days past the printed date if no spoilage signs are present.

What does spoiled pesto smell like?

Spoiled pesto typically develops a sour, fermented, or "off" smell that's clearly different from fresh. Trust your nose — it's a reliable spoilage detector.

Will I get sick from eating spoiled pesto?

Possibly. Most foodborne illness comes from bacteria you can't see, smell or taste. Symptoms appear 1–48 hours after eating: nausea, vomiting, diarrhea, cramps. If symptoms last more than 48 hours, see a doctor.

How to Tell if Pesto Has Gone Bad — 2026 Spoilage Signs (USDA)

The 5-second spoilage check

Use your senses in this order: look, smell, touch, taste (taste only if everything else passes, and only a tiny amount). Any single warning sign means toss it.

Visual signs pesto has gone bad

Black on top is oxidation (normal)
Mold
Sour smell

Smell test

Fresh pesto should smell clean and characteristic of itself. A sour, ammonia-like, fermented, sulfurous, or just plain "off" smell means bacteria have multiplied. The nose detects spoilage compounds at concentrations far below dangerous bacterial levels — if it smells bad, it is bad.

Texture changes

Slime is the most reliable spoilage indicator after smell. A film, sticky surface, or unusual softness/hardness signals bacterial breakdown. Mold growth (fuzzy spots) means there are also invisible mold fibers and possibly mycotoxins throughout — toss the entire item, not just the visible patch.

Can you eat pesto past the expiration date?

"Best by", "use by" and "sell by" dates are quality estimates set by manufacturers — not safety cutoffs. Most foods are still safe for some time past these dates if no spoilage signs are present and they've been stored correctly. Trust your senses over the printed date.

Common mistakes that speed spoilage

Top with olive oil to seal
Freeze in cubes for portion control
Homemade lasts 3-5 days

What to do if you ate spoiled pesto

Don't induce vomiting. Most cases resolve on their own.
Hydrate. Sip water, oral rehydration solution, or clear broth.
Rest. Let your digestive system work through it.
See a doctor if symptoms last more than 48 hours, you have a fever above 102°F, blood in vomit/stool, or signs of severe dehydration.
High-risk groups (pregnant, elderly, immunocompromised, young children) should consult a doctor sooner.

How to tell if pesto is bad