How to Store Natto: Keep Your Fermented Soybeans Fresh and Flavorful

Natto is one of Japan's most beloved fermented foods — a powerhouse of probiotics, protein, and that unmistakable sticky, stringy texture. Whether you've just finished a home fermentation batch or picked up a pack from your local Asian grocery store, knowing how to store natto properly is essential to preserving its nutritional value, flavor, and beneficial bacteria. Done right, natto can stay delicious and alive for weeks in the fridge or months in the freezer.

Understanding Natto Before You Store It

Before diving into storage methods, it helps to understand what makes natto unique. Natto is made from soybeans fermented with Bacillus subtilis var. natto, a beneficial bacteria that remains alive and active even after fermentation is complete. This means natto is a living food — and like all living things, it continues to change over time.

As natto ages, several things happen:

• The ammonia smell intensifies — a natural byproduct of continued bacterial activity
• The strings become stickier and more pronounced
• The flavor deepens, becoming more pungent and complex
• Color may shift from pale yellow to a darker, brownish hue

None of these changes are necessarily signs of spoilage, but they do indicate that proper storage is critical to slowing this ongoing fermentation process and maintaining the quality you want.

Refrigerator Storage: The Everyday Method

For most people, the refrigerator is the go-to storage solution for natto. Cold temperatures significantly slow the activity of Bacillus subtilis, essentially pausing the fermentation without killing the bacteria.

How to refrigerate natto properly:

1. Cool it down first — If you've just finished a homemade batch, allow the natto to cool to room temperature before refrigerating. Placing hot or warm natto directly in the fridge can cause condensation and affect texture.
2. Portion it out — Divide natto into single-serving portions before storing. This minimizes repeated exposure to air and temperature changes every time you open the container.
3. Use airtight containers — Glass jars with tight-fitting lids or BPA-free plastic containers work well. If your natto came in its original styrofoam or paper packaging, transfer it to a sealed container for longer storage.
4. Keep it at the back of the fridge — The back of the refrigerator maintains a more consistent temperature. Avoid door shelves, where temperatures fluctuate every time the door opens.
5. Label with the date — Always note when you stored it so you can track freshness.

Refrigerator shelf life: Properly stored natto will stay fresh and flavorful for 7 to 10 days in the refrigerator. Homemade natto is generally best consumed within this window, while commercially packaged natto often has a printed use-by date of around 7–14 days from production.

Freezer Storage: Long-Term Preservation

Freezing natto is an excellent option if you've made a large batch or want to extend shelf life significantly. The good news? Bacillus subtilis is remarkably cold-tolerant — freezing does not kill the beneficial bacteria. Once thawed, your natto will bounce back to life and retain most of its probiotic benefits.

How to freeze natto properly:

1. Portion before freezing — Just like refrigerator storage, divide natto into individual serving sizes before freezing. This way, you only thaw what you need.
2. Wrap tightly — Wrap each portion in plastic wrap or wax paper, then place in a zip-lock freezer bag or airtight container. Remove as much air as possible to prevent freezer burn.
3. Double-bag for odor control — Natto's strong aroma can permeate your freezer if not properly sealed. A double-bag method provides extra protection.
4. Freeze flat — If using freezer bags, lay them flat for efficient use of space and faster, more even thawing.
5. Label clearly — Include the date and contents on each package.

Freezer shelf life: Frozen natto maintains excellent quality for 2 to 3 months. It can technically be safe beyond this window, but texture and flavor may begin to degrade.

Thawing frozen natto:

• Transfer natto from the freezer to the refrigerator and allow it to thaw overnight — this is the gentlest method.
• For faster thawing, leave it at room temperature for 30–60 minutes.
• Avoid microwaving natto to thaw it, as high heat can kill the beneficial bacteria and alter the texture dramatically.

Storing Commercially Packaged Natto

If you buy natto from a store rather than making it at home, the storage principles are the same, but there are a few additional considerations:

• Keep refrigerated from the moment of purchase — Don't leave commercial natto at room temperature for extended periods during grocery trips.
• Respect the use-by date — Commercial natto is carefully timed for peak quality. While it may still be safe shortly after this date, the texture and flavor will decline.
• Freeze before the use-by date — If you can't consume all your purchased natto in time, freeze it before the date on the package for best results.
• Condiment packets — Most commercial natto comes with small packets of soy sauce and mustard. These can be stored separately in the refrigerator or discarded; they do not need to be frozen.

Tips for Maintaining Natto Quality During Storage

A few extra habits will make a meaningful difference in your stored natto's quality:

• Minimize air exposure — Every time natto is exposed to air, oxidation occurs and flavor degrades. Use appropriately sized containers to limit headspace.
• Don't mix old and new batches — Combining a fresh batch with an older one speeds up the aging process for the newer natto.
• Store away from strong-smelling foods — Even in airtight containers, natto can exchange odors with particularly pungent neighbors like aged cheese or durian.
• Bring to room temperature before eating — Cold natto straight from the fridge can taste muted. Allow it to sit for 10–15 minutes before serving to bring out its full flavor profile.

Frequently Asked Questions

How long does homemade natto last compared to store-bought? Homemade natto generally lasts 7 to 10 days in the refrigerator, while commercially packaged natto is often good for 7 to 14 days thanks to controlled fermentation conditions and packaging. Both can be frozen for up to 3 months without significant quality loss.

Can I store natto at room temperature? Only for very short periods — a few hours at most. Room temperature allows Bacillus subtilis to continue fermenting actively, which will rapidly intensify the ammonia smell and alter texture. Never leave natto at room temperature overnight.

Does freezing natto kill the beneficial bacteria? No! Bacillus subtilis is a spore-forming bacterium, which means it can survive freezing temperatures in a dormant state. Once thawed, the bacteria reactivate, and your natto retains its probiotic benefits.

Why does my natto smell more like ammonia after a few days in the fridge? This is completely normal. The bacterial activity doesn't fully stop in the fridge — it just slows down. Over several days, continued breakdown of proteins produces ammonia as a natural byproduct. A mild ammonia scent is normal; a very strong, overwhelming smell may indicate your natto has been stored too long or at improper temperatures.