How to Tell if a Potato Is Bad: 7 Clear Warning Signs

A bad potato shows visible mold, deep soft spots, a foul odor, or extensive green discoloration. Sprouts longer than 1 inch and wrinkled, shrunken skin also indicate spoilage. When in doubt, discard the potato to avoid potential solanine poisoning.

Discover exactly how to identify spoiled potatoes with this practical guide. You'll learn the critical visual, textural, and olfactory signs that distinguish safe-to-eat potatoes from those that could make you sick. This comprehensive resource covers everything from minor imperfections you can safely cut away to dangerous spoilage indicators that require immediate disposal.

Visual Indicators of Spoilage: What to Look For

When examining potatoes, your eyes provide the first line of defense against spoiled produce. Proper visual assessment prevents food waste while protecting your health.

The USDA Food Safety and Inspection Service recommends checking for these critical visual markers:

Condition	Safe to Eat?	Action Required
Small green spots (less than 10% surface)	Yes, after proper preparation	Peel deeply to remove all green areas
Extensive green discoloration (more than 30% surface)	No	Discard entire potato
Surface mold (fuzzy spots)	No	Discard entire potato
Sprouts under 1 inch	Yes, after proper preparation	Remove sprouts and eyes completely
Deep soft spots or dark lesions	No	Discard entire potato

Texture Tells the Truth: What Your Fingers Reveal

After visual inspection, gently squeeze the potato to assess its texture. Healthy potatoes feel firm and solid throughout. Warning signs include:

• Soft or mushy spots - indicates advanced decay beneath the skin
• Wrinkled, shrunken skin - shows significant moisture loss and age
• Wet, slimy surface - signals bacterial growth
• Hollow areas when squeezed - means internal breakdown has occurred

According to research published in the Postharvest Biology and Technology journal, potatoes begin developing internal defects after 3-4 weeks of improper storage, often before visible signs appear on the surface.

Smell Test: Your Nose Knows

Your sense of smell provides crucial information about potato freshness. Fresh potatoes have an earthy, slightly sweet aroma. Warning signs include:

• Vinegar-like sourness - indicates fermentation has begun
• Musty, moldy odor - even without visible mold
• Chemical or bitter smell - suggests solanine development
• Complete absence of smell - may indicate advanced decay

When multiple potatoes are stored together, a single spoiled specimen can affect the entire batch. If one potato smells off, inspect all nearby potatoes carefully.

Understanding Sprouts and Green Spots: When to Worry

Sprouting and greening represent the two most common concerns for potato consumers. Here's what you need to know:

Sprouting Timeline and Safety

Potatoes begin sprouting within 2-3 weeks under typical kitchen conditions. The sprouting process follows this progression:

1. Days 1-7: Small buds form at the eyes
2. Days 7-14: Sprouts grow to 1/4-1/2 inch
3. Days 14-21: Sprouts exceed 1 inch and become woody
4. Days 21+: Sprouts draw significant nutrients from the tuber

According to the FDA Foodborne Illness guidelines, potatoes with sprouts under 1 inch remain safe to eat after complete removal of sprouts and eyes. Potatoes with extensive sprouting (over 1 inch) should be discarded as they've lost significant nutritional value and may contain elevated solanine levels.

Green Spots Explained

Green discoloration occurs when potatoes are exposed to light, triggering chlorophyll production and accompanying solanine development. The relationship between green color and solanine concentration isn't always proportional, making visual assessment alone insufficient.

A study by the USDA Agricultural Research Service found that green areas contain 2-5 times more solanine than non-green portions. When green discoloration covers more than 30% of the surface, the entire potato likely contains unsafe solanine levels.

When Slightly Imperfect Potatoes Are Still Safe

Not all imperfections mean automatic disposal. Many potatoes with minor issues can be safely consumed after proper preparation:

• Small green spots: Peel deeply (1/4 inch minimum) to remove affected areas
• Minor sprouting: Remove all sprouts and eyes completely
• Surface blemishes: Cut away affected areas with 1/2 inch margin
• Wrinkled skin: If texture remains firm underneath, still usable

The CDC Food Safety guidelines emphasize that cutting away spoiled portions works only when decay is localized. If spoilage appears throughout the potato, discard the entire specimen.

Danger Signs That Require Immediate Disposal

Certain conditions make potatoes unsafe for consumption. Discard potatoes showing any of these critical warning signs:

• Visible mold in any quantity (mold roots penetrate deep beneath surface)
• Extensive soft spots or mushy texture throughout
• Foul odor indicating advanced decomposition
• Wet, slimy surface suggesting bacterial growth
• Large green areas covering more than 30% of the surface

Consuming potatoes with these characteristics risks solanine poisoning, which can cause nausea, headaches, and in severe cases, neurological symptoms. The National Agricultural Library reports that cooking does not destroy solanine, making proper identification crucial.

Proper Storage Techniques to Extend Freshness

Preventing spoilage starts with proper storage. Follow these evidence-based recommendations:

• Temperature: Store between 45-50°F (7-10°C) - never refrigerate
• Humidity: Maintain 90-95% humidity to prevent moisture loss
• Light: Keep in complete darkness to prevent greening
• Ventilation: Use breathable containers like paper bags or baskets
• Separation: Store away from onions, which accelerate sprouting

Under optimal conditions, most potato varieties remain fresh for 2-3 months. The University of Minnesota Extension confirms that proper storage reduces spoilage by up to 70% compared to room temperature storage.

Food Safety Considerations for Vulnerable Groups

Certain populations face higher risks from consuming compromised potatoes:

• Pregnant women should avoid potatoes with any green discoloration
• Young children have lower tolerance for solanine compounds
• Immunocompromised individuals face greater risk from bacterial contamination
• Older adults may experience more severe symptoms from foodborne illness

When serving these groups, exercise extra caution and discard any potatoes showing even minor signs of spoilage.

Common Questions About Potato Spoilage

These frequently asked questions address the most common concerns about identifying bad potatoes:

Can I eat a potato that has sprouted?

Potatoes with small sprouts (under 1 inch) are safe to eat after completely removing all sprouts and eyes. Potatoes with extensive sprouting (over 1 inch) should be discarded as they've lost nutritional value and may contain elevated solanine levels.

How much green on a potato is dangerous?

Any green discoloration indicates solanine development. Small green spots (less than 10% of surface) can be safely removed by peeling deeply (1/4 inch minimum). Potatoes with green covering more than 30% of the surface should be discarded entirely as solanine likely permeates the entire potato.

What does a bad potato smell like?

A bad potato develops distinct off-odors including vinegar-like sourness (indicating fermentation), musty or moldy smells, or chemical/bitter odors signaling solanine development. Fresh potatoes should have a mild, earthy aroma. Any strong or unpleasant odor means the potato has spoiled.

Can cooking destroy solanine in potatoes?

No, cooking does not destroy solanine. Boiling, baking, or frying reduces but doesn't eliminate this toxic compound. The only safe approach is to remove green areas completely or discard potatoes with extensive greening. Proper storage in darkness prevents solanine development in the first place.

How long do potatoes stay fresh after purchase?

Properly stored potatoes remain fresh for 2-3 months. At room temperature, they typically last 1-3 weeks. Refrigeration accelerates sugar conversion, creating off-flavors. The key factors are cool temperature (45-50°F), high humidity, and complete darkness. Check weekly for any signs of spoilage.