Recognizing Spoiled Food: Signs by Category

Home-Canned Foods

Home-canned foods carry the highest risk of serious foodborne illness because improper processing can produce conditions for botulism without any visible sign.

Discard immediately if:

• Lid bulges upward (gas produced inside the jar)
• Lid does not seal — it flexes when pressed in the center
• Liquid spurts out when the lid is removed
• Foam or bubbling appears when opened
• Hissing sound when lid is removed
• Off, fermented, or unusual odor
• Any mold visible inside the jar
• Liquid is unusually cloudy or discolored compared to when packed
• Food looks mushy or has unusual texture

Critical note: Botulism toxin produces NONE of these signs in many cases. The food can look, smell, and taste completely normal. For this reason, the USDA recommends boiling all home-canned low-acid foods (vegetables, meats, beans) for 10 minutes before eating. This destroys any toxin that may be present, even if the food appears normal.

Commercially Canned Foods

Commercial canning is highly reliable, but cans can fail.

Discard if:

• Deeply dented along a seam or at the top/bottom edge (dents at the side of the can away from seams are generally safe but inspect carefully)
• Bulging top or bottom (internal gas production)
• Rusted through or perforated
• Spurting when opened
• Off smell when opened
• The can has no code or label and you cannot identify contents/date

Acceptable: Minor surface rust that wipes off and hasn't penetrated the metal. Slight discoloration of the can exterior. Seam dents that are shallow and away from the seams.

Fresh Meats

Discard if:

• Slimy or tacky texture (bacterial biofilm)
• Sour, sulfurous, or ammonia-like smell
• Gray or green discoloration (beyond the normal graying of cut surfaces exposed to air)
• Mold visible on the surface

Normal appearances that are not spoilage:

• Pink or red discoloration from myoglobin oxidation (brown surface on cut beef exposed to air is normal and doesn't indicate spoilage)
• Liquid in the package (normal purge)
• Slight discoloration at the center of ground beef when the outside is red (lack of oxygen, not spoilage)

The two-hour rule: Raw meat left above 40°F for more than 2 hours (cumulative) is in the temperature danger zone. Discard after 2 hours unrefrigerated, regardless of appearance.

Cooked Meats and Leftovers

Discard if:

• More than 3-4 days in the refrigerator
• Slimy surface texture
• Off smell
• Mold visible
• Was unrefrigerated for more than 2 hours

Power outage rule: If the power was out and refrigerator temperature rose above 40°F for more than 2 hours, discard all raw meat, poultry, fish, dairy, and leftovers. A refrigerator maintains safe temperature for approximately 4 hours if the door stays closed.

Dairy

Milk: Sour smell, curdled or lumpy texture, yellow or pink tinge. Discard.

Cheese: Mold on hard cheese (cheddar, parmesan, Swiss) — cut off at least 1 inch around and below the mold spot. The rest is safe. Mold on soft cheese (brie, ricotta, cottage cheese, cream cheese) means discard the entire package — mold penetrates soft cheese throughout.

Butter: Rancid, soapy, or unusually sharp smell. Discard.

Eggs: Float test — fresh eggs sink and lay flat; older but still safe eggs tilt upright; rotten eggs float. Cracked eggs should be used immediately or discarded. Bad smell when cracked open means discard.

Fresh Produce

General principle: Surface mold on firm produce (hard squash, cabbage) can often be cut away with generous margin. Surface mold on soft produce (berries, tomatoes, cucumbers) or any mold that has penetrated the interior means discard the item.

Discard if:

• Berries/grapes: moldy, mushy, fermented smell
• Tomatoes: soft and oozing, large mold spots
• Leafy greens: slimy, black, or strongly bad-smelling
• Root vegetables: soft spots throughout, heavy mold penetrating the flesh

Surface deterioration vs. deep spoilage: A wilted carrot or soft apple is not unsafe — it's just past peak quality. Mold penetrating the flesh or bacterial rot (soft and oozing with off smell) is unsafe.

Grains and Dry Goods

Discard if:

• Weevils, pantry moths, or visible insect activity (weevil frass looks like fine sawdust; moth webbing is visible in corners of packages)
• Musty or off smell when the container is opened
• Clumping or moisture visible inside a sealed container (moisture intrusion)
• Mold visible in any form

Grains with visible weevils: The grain is still edible if you remove the insects. Sift, freeze the grain for 72 hours to kill any remaining insects and eggs, then store properly. The decision is personal — contaminated grain is nutritionally safe, just unpleasant.

Home-Preserved Foods (Dehydrated, Fermented, Cured)

Dehydrated food — discard if:

• Moisture condensation inside the storage container
• Mold visible on any piece
• Off or rancid smell

Fermented vegetables (sauerkraut, pickles) — discard if:

• Pink, orange, or black mold below the brine surface
• Strong, uncharacteristic off smell (not the normal sour ferment smell)
• Slimy texture of the vegetables themselves (not just the brine)

Cured meats — discard if:

• Slimy surface under the rind
• Putrid smell rather than the expected cured meat smell
• Green or black mold penetrating deep into the muscle (surface white or blue-green mold on some dry-cured products is normal and brushed off — deep mold is not)