How to Tell if Natto Has Spoiled: A Guide to Identifying Rotten Natto

Identifying Spoiled Natto: A Guide to Ensuring Food Safety

Natto is a unique fermented food with a distinctive sticky texture and strong flavor loved by many. But like any fermented food, natto can spoil and become unsafe to eat if not stored properly. How can you tell if your natto has gone bad? This comprehensive guide covers everything from optimal storage methods to clear signs of spoiled natto.

An Overview of Natto

Natto originated in ancient Japan as a clever way to preserve soybeans using fermentation. The beans are inoculated with Bacillus subtilis bacteria and then left to ferment, creating natto's distinctive slimy texture and powerful aroma. Nutritionally, natto is rich in protein, fiber, vitamin K2, and probiotics.

The fermentation process gives natto a short shelf life. Fresh natto will keep for about a week in the fridge, though many sources say 3-4 days is ideal for peak quality. Freeze any unused portions to extend the shelf life. But even with proper storage, natto can still spoil if left for too long.

How to Store Natto Correctly

Follow these tips for storing natto optimally to avoid spoilage:

• Keep natto refrigerated at all times, as warmth speeds fermentation and spoilage.
• Leave natto in its original packaging or transfer to an airtight container.
• Ensure your fridge temperature is set below 40°F (5°C).
• Avoid opening the natto package repeatedly, as oxygen promotes spoilage.
• Use natto within 3-4 days of opening for best quality.
• Freeze extra natto in airtight bags or containers to extend shelf life.

How to Identify Spoiled Natto

Despite proper storage methods, natto will eventually spoil once fermentation progresses too far. Look for these signs to determine if your natto has gone bad:

Appearance

• Excessive sliminess or stickiness
• Unnaturally dark color
• Presence of black, green, or colorful mold
• Liquid in package is cloudy or bubbly
• Beans are shriveled or dried out

Smell

• Putrid, rotting odor
• Sour, ammonia-like smell
• Very strong, pungent aroma

Texture

• Soft or mushy beans
• Extreme stickiness
• Slimy film on top of package

If your natto exhibits any of these red flags, err on the side of caution and throw it away. Consuming spoiled natto can cause food poisoning.

Safely Tasting Questionable Natto

If you're unsure about a package of natto, there are ways to test it safely:

• First inspect visually for mold, off colors, etc.
• Give it a sniff - spoiled natto smells rancid.
• Try a small sample of beans - discard if mushy or sour.
• Wait 24 hours after sampling to check for illness.
• When in doubt, remember "If smelly, don't eat jelly."

Avoiding Natto Spoilage Through Proper Handling

In addition to storage methods, how you handle natto also impacts shelf life. Follow these best practices to keep natto fresher for longer:

Purchase Quality Natto

High-quality natto from a reputable producer will resist spoilage better than poor quality batches. Check expiration dates and packaging carefully when purchasing.

Inspect Packaging

Inspect natto packaging before buying. Avoid any with tears, punctures, or air bubbles, as these allow oxygen to speed spoilage.

Use Clean Utensils

Always use clean utensils and dishes when taking natto out of the package to prevent cross-contamination. Dirty tools can introduce spoilage bacteria.

Limit Air Exposure

Limit how much natto gets exposed to air when opened, as oxygen can advance fermentation. Only remove what you plan to eat soon.

Portion Leftovers

Once opened, divide leftover natto into small portions in airtight containers to minimize air exposure. Use within 3-4 days.

Practice Proper Hygiene

Wash hands thoroughly before handling natto. Good personal hygiene prevents transfer of bacteria from hands to food.

Sanitize Surfaces

Clean counters, utensils, and storage containers with soap and hot water before using to prevent contamination.

Troubleshooting Common Causes of Natto Spoilage

If you find your natto keeps spoiling prematurely, examine your storage habits and handling to identify any problematic practices. Here are some common causes of early natto spoilage:

Storing at Room Temperature

Leaving natto unrefrigerated allows fermentation and spoilage to accelerate. Always store fresh and opened natto in the fridge.

Saving Leftovers Too Long

Natto left in the fridge more than 3-4 days after opening has likely spoiled. Stick to the recommended storage times.

Freezing and Thawing Improperly

Letting frozen natto thaw and refreeze rather than thawing once can damage texture and enhance spoilage. Defrost frozen portions fully before use.

Using Dirty Utensils

Unclean tools and containers can introduce new bacteria that hasten spoilage. Always wash adequately before prepping natto.

Checking Infrequently

Failing to inspect natto regularly can allow spoilage to progress undetected. Check daily for visible signs.

Cooking Incorrectly

Overcooking natto kills the beneficial bacteria that keep harmful microbes at bay. Heat just until warm, not boiling.

How to Use Natto Safely in Recipes

You can decrease food safety risks when cooking with natto by following these best practices:

Inspect Before Use

Examine natto closely and smell before adding to recipes. Discard any with signs of spoilage.

Cook Thoroughly

Ensure any dishes containing natto are cooked to safe internal temperatures to destroy pathogens.

Avoid Cross-Contamination

Use separate utensils and surfaces for raw natto to prevent spread of bacteria to other ingredients.

Chill Leftovers Rapidly

Refrigerate any unused natto immediately after cooking. Don't leave at room temperature.

Reheat Fully

Only reheat natto dishes until piping hot throughout before serving leftovers.

When in Doubt, Throw it Out

If you have any concerns about the safety of a natto dish, play it safe and discard it.

Fermenting Natto at Home Safely

Traditionally, Japanese households made their own natto. Follow these food safety guidelines if fermenting natto yourself:

Source Quality Beans

Select fresh, organic soybeans. Avoid old beans with cracks or damage that allow spoilage bacteria to enter.

Sanitize Equipment

Thoroughly wash any jars, weights, etc. used in fermenting to destroy lurking microbes.

Control Conditions

Maintain proper temperature and humidity during fermentation to prevent pathogenic bacterial growth.

Monitor Closely

Inspect home fermented natto daily for any signs of spoilage like odd textures, colors or smells.

Check pH

Test finished natto's pH to ensure it's below 4.6, the level that inhibits dangerous toxin production.

When Doubtful, Toss it Out

If any batch looks or smells off, don't risk getting sick - compost it instead.

The Takeaway

Avoiding natto spoilage requires storing it properly, handling with care, and inspecting regularly for signs of fermentation going too far. Refrigerate promptly after opening, portion for minimal air exposure, and discard any natto with an off appearance, texture or smell. With good food safety practices, you can continue enjoying natto's unique flavor and nutrition safely.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.