What is natto starter and why do I need it?

Natto starter is a powdered or liquid preparation of Bacillus subtilis var. natto — the specific bacterial strain that ferments cooked soybeans into natto. It is the only reliable way to make natto at home outside of using a store-bought natto bootstrap. Without this exact strain, soybeans will not develop the characteristic stringy texture and umami profile. Wild Bacillus subtilis from rice straw or the environment is too inconsistent for home fermentation.

How much natto starter do I need per batch?

A typical batch (200–250g dry soybeans, 500–600g cooked) needs about 0.5g of powdered natto starter — roughly 1/4 teaspoon. One small packet (typically 3g, sold by NYrture, Cultures for Health, or imported Japanese brands) makes 6–10 batches. A single packet costs $8–15 and works out to roughly $1–2 worth of starter per batch. The Bacillus subtilis is highly active — over-inoculation does not improve the result and can produce off flavors.

Can I use store-bought natto as a starter instead?

Yes. Mix 1 tablespoon of fresh (not frozen, not pasteurized) store-bought natto with 1 tablespoon of warm 40°C water and stir to distribute the bacteria. Pour over your cooked soybeans during inoculation. This works reliably for 2–3 generations of home batches before bacterial vigor decreases. After that, refresh from a new pack of store-bought natto or from powdered starter. Many home fermenters alternate: bootstrap from store-bought when natto is available locally, fall back to powdered starter when it is not.

How long does natto starter keep?

Powdered Bacillus subtilis natto starter keeps 2 years unopened at room temperature, and 6–12 months opened if kept in a cool dry place (refrigeration extends life). The bacteria are in spore form, which is highly stable — temperature swings and brief humidity exposure do not kill them. Once you open a packet, transfer any unused powder to a small airtight container with a desiccant packet for best long-term storage. Liquid starters keep 3 months refrigerated.

Where do I buy natto starter in the US?

Three primary US sources: NYrture (Brooklyn, founded by Anne Yamada, sells fresh natto and starter), Cultures for Health (broad fermentation supplier, ships powdered natto starter), and GEM Cultures (longtime US supplier of Japanese fermentation cultures including natto). Amazon also carries imported Japanese natto starter packets, though brand consistency varies by listing. Avoid generic 'probiotic Bacillus subtilis' products from supplement aisles — those are different strains optimized for digestion claims, not for natto fermentation.

Where do I buy natto starter outside the US?

In Japan: Higuchi Matsunosuke Shoten (founded 1912 in Mito, the original commercial natto starter producer) and Naruse Hatsuga Shoji are the two reliable suppliers. In Europe: order direct from Japan via Mitoku, or through a few specialty fermentation shops in the UK and Germany. In Australia and New Zealand: Cultures for Health and Amazon import listings are the most accessible options. In India: search Amazon India for 'natto starter Bacillus subtilis' — GEM Cultures and Cultures for Health both ship internationally.

How much does natto starter cost?

US retail: $8–15 for a 3g powder packet (enough for 6–10 batches). NYrture sells a 3-pack of fresh natto with culture for $30–35. Cultures for Health single packets run $9–12. Direct from Japan via international shipping: starter itself is $4–6 per packet, but shipping triples the total. Per-batch starter cost is roughly $1–2 — a marginal expense compared to the soybeans, electricity, and time invested. Cost is rarely the deciding factor; availability and shipping speed usually matter more.

Do I need refrigerated shipping for natto starter?

No — powdered Bacillus subtilis natto starter ships at room temperature. The bacteria are in heat-stable spore form and survive normal shipping conditions including summer heat in transit. Liquid starters or fresh natto (when shipped as a starter source) do require cold-pack shipping; expect to pay a premium for that service from suppliers like NYrture. For most home fermenters the powdered form is the practical choice — cheaper to ship, longer to store, easier to dose.

Where to Buy Natto Starter (Bacillus subtilis natto): A Practical Guide

Pick the path that matches your situation

I am in the US and want to start within a week: order from NYrture or Cultures for Health on Amazon — both ship powdered starter Prime, both arrive in 2–4 days. Skip to NYrture below.
I have access to fresh natto already: use the bootstrap method — 1 tbsp of store-bought natto plus warm water replaces a powder packet for 2–3 generations. Skip to bootstrap method.
I am in Japan or willing to import: Higuchi Matsunosuke Shoten (the original since 1912) sells the most consistent powdered starter at the lowest per-packet price. Skip to international sourcing.
I want long-term cheapest-per-batch: buy one powder packet and refresh from your own batches every 2–3 generations using the bootstrap method. Most fermenters end up here.

The Four Sources Worth Knowing

1. NYrture — the US specialist

Brooklyn-based natto specialist founded by Anne Yamada (formerly of Aedan Fermented Foods). NYrture sells both fresh natto and natto starter direct, and is the single most accessible high-quality US source. Packets are 3g (~10 batches each). The brand has a reputation for consistent fermentation results and clear documentation — the single best entry point if you have never made natto before.

Buy this if: you are in the US, you want fast shipping, or you want a supplier whose primary product is natto (not a generic fermentation starter line).

Price: $12–15 per starter packet; fresh natto trays $10–15 each.

Find NYrture natto starter on Amazon →

2. Cultures for Health — the generalist option

Long-running US fermentation supplier (acquired by NWF in 2019). Sells a powdered Bacillus subtilis natto starter alongside their full kefir, kombucha, sourdough, and yogurt culture lines. The natto starter is reliable but the brand is not natto-specialized — expect generic packaging and no extensive natto-specific documentation. Good fallback if NYrture is out of stock.

Buy this if: NYrture is sold out, you already buy from Cultures for Health for other ferments, or you want a single-vendor fermentation cupboard.

Price: $9–12 per packet.

Find Cultures for Health natto starter on Amazon →

3. GEM Cultures — the international shipper

One of the oldest US suppliers of Japanese fermentation cultures (also a primary source for tempeh starter and koji spores). GEM ships internationally, which is the main reason fermenters outside the US end up there. Packets are smaller (1–2g) but at lower per-packet cost. The bacterial vigor is consistent — this company has been doing this since the 1980s.

Buy this if: you are outside the US, you want international shipping, or you also need koji spores or tempeh starter from the same vendor.

Price: $8–10 per packet plus international shipping.

4. Higuchi Matsunosuke Shoten — direct from Japan

The original commercial natto starter producer, founded in 1912 in Mito (the historical home of Japanese natto). Higuchi supplies most commercial natto manufacturers in Japan and sells direct to fermenters in 3g and 10g packets. Highest bacterial consistency, lowest per-packet price — but international shipping is the blocker. Best ordered as part of a larger Japan-pantry import, split across a fermentation group, or sourced through a re-importer.

Buy this if: you are in Japan, you import regularly from Japan, or you ferment in volume and want the most consistent strain available.

Price: ¥600–1,200 per packet ($4–8) plus shipping; minimum order quantities vary by reseller.

The Bootstrap Method: Use Store-Bought Natto Instead

If you can buy fresh natto locally — at Mitsuwa, H Mart, or a larger Whole Foods — you can skip the starter purchase entirely for the first 2–3 batches. The bacteria in commercial natto are still alive (assuming the natto is refrigerated and not frozen or pasteurized).

Method:

Use 1 tbsp of fresh natto per 200–250g dry soybeans. Frozen natto works if thawed in the fridge first; pasteurized natto does not.
Mix the natto with 1 tbsp of warm 40°C water in a small bowl. Stir to distribute the bacteria.
Pour the inoculant over freshly cooked soybeans while they are still warm (45°C ideal). Mix gently.
Ferment as usual — 22–24 hours at 40–45°C. See How to Make Natto for the full method.

This works reliably for 2–3 generations of home batches. After that, the bacterial vigor decreases noticeably — the strings are weaker, fermentation is slower. Refresh from a new pack of store-bought natto, or commit to a powdered starter for longer-term consistency.

The hybrid strategy most home fermenters land on: buy one packet of powdered starter as your baseline, then bootstrap from your own batches between purchases. A single $12 packet plus periodic store-bought refreshes can supply a once-a-month natto habit for over a year.

How to Store Starter Once You Have It

Powdered Bacillus subtilis natto is in spore form — highly stable, but worth storing well to maximize the life of an opened packet.

Unopened: 2 years at room temperature in the original sealed packet. Keeps best in a cool dry cupboard.
Opened: transfer to a small airtight container (a 30ml glass jar with a tight-sealing lid works well) along with a food-grade silica gel packet to absorb moisture. Refrigerated, it keeps 12 months easily; at room temperature, 6–9 months.
What kills it: sustained moisture exposure (the spores can germinate in a damp container and then die without soybeans to feed on). Do not store in a humid kitchen drawer or near steam.

What Not to Buy

Generic “Bacillus subtilis” supplements from probiotic aisles. These are different strains optimized for gut-health claims, not for natto fermentation. Many are Bacillus subtilis var. spizizenii or other variants that produce no stringiness.
Frozen natto for starter use. Freezing substantially reduces bacterial viability. It still works for eating, but use a fresh refrigerated pack as the bootstrap source instead.
Pasteurized natto. Some shelf-stable natto products are heat-treated. The flavor is intact but the bacteria are dead — useless for inoculation.
Old packets from unknown sellers. Amazon listings with no clear origin or undated stock can produce dead-on-arrival starter. Stick to NYrture, Cultures for Health, GEM Cultures, or named Japanese imports with visible production dates.

Adjacent Pages

How to Make Natto — the full fermentation method, Instant Pot specifics, and troubleshooting
What Is Natto — the entity background: nutrition, history, and what Bacillus subtilis natto actually does
Fermentation Hub — miso, shio koji, amazake, and other home-fermentation projects
What Is Koji — the other Japanese culture worth keeping in your fermentation cupboard, useful for shio koji and amazake
Japanese Pantry — where natto sits in the broader Japanese ingredient landscape

Frequently Asked Questions

What is natto starter and why do I need it?: Natto starter is a powdered or liquid preparation of Bacillus subtilis var. natto — the specific bacterial strain that ferments cooked soybeans into natto. It is the only reliable way to make natto at home outside of using a store-bought natto bootstrap. Without this exact strain, soybeans will not develop the characteristic stringy texture and umami profile. Wild Bacillus subtilis from rice straw or the environment is too inconsistent for home fermentation.
How much natto starter do I need per batch?: A typical batch (200–250g dry soybeans, 500–600g cooked) needs about 0.5g of powdered natto starter — roughly 1/4 teaspoon. One small packet (typically 3g, sold by NYrture, Cultures for Health, or imported Japanese brands) makes 6–10 batches. A single packet costs $8–15 and works out to roughly $1–2 worth of starter per batch. The Bacillus subtilis is highly active — over-inoculation does not improve the result and can produce off flavors.
Can I use store-bought natto as a starter instead?: Yes. Mix 1 tablespoon of fresh (not frozen, not pasteurized) store-bought natto with 1 tablespoon of warm 40°C water and stir to distribute the bacteria. Pour over your cooked soybeans during inoculation. This works reliably for 2–3 generations of home batches before bacterial vigor decreases. After that, refresh from a new pack of store-bought natto or from powdered starter. Many home fermenters alternate: bootstrap from store-bought when natto is available locally, fall back to powdered starter when it is not.
How long does natto starter keep?: Powdered Bacillus subtilis natto starter keeps 2 years unopened at room temperature, and 6–12 months opened if kept in a cool dry place (refrigeration extends life). The bacteria are in spore form, which is highly stable — temperature swings and brief humidity exposure do not kill them. Once you open a packet, transfer any unused powder to a small airtight container with a desiccant packet for best long-term storage. Liquid starters keep 3 months refrigerated.
Where do I buy natto starter in the US?: Three primary US sources: NYrture (Brooklyn, founded by Anne Yamada, sells fresh natto and starter), Cultures for Health (broad fermentation supplier, ships powdered natto starter), and GEM Cultures (longtime US supplier of Japanese fermentation cultures including natto). Amazon also carries imported Japanese natto starter packets, though brand consistency varies by listing. Avoid generic 'probiotic Bacillus subtilis' products from supplement aisles — those are different strains optimized for digestion claims, not for natto fermentation.
Where do I buy natto starter outside the US?: In Japan: Higuchi Matsunosuke Shoten (founded 1912 in Mito, the original commercial natto starter producer) and Naruse Hatsuga Shoji are the two reliable suppliers. In Europe: order direct from Japan via Mitoku, or through a few specialty fermentation shops in the UK and Germany. In Australia and New Zealand: Cultures for Health and Amazon import listings are the most accessible options. In India: search Amazon India for 'natto starter Bacillus subtilis' — GEM Cultures and Cultures for Health both ship internationally.
How much does natto starter cost?: US retail: $8–15 for a 3g powder packet (enough for 6–10 batches). NYrture sells a 3-pack of fresh natto with culture for $30–35. Cultures for Health single packets run $9–12. Direct from Japan via international shipping: starter itself is $4–6 per packet, but shipping triples the total. Per-batch starter cost is roughly $1–2 — a marginal expense compared to the soybeans, electricity, and time invested. Cost is rarely the deciding factor; availability and shipping speed usually matter more.
Do I need refrigerated shipping for natto starter?: No — powdered Bacillus subtilis natto starter ships at room temperature. The bacteria are in heat-stable spore form and survive normal shipping conditions including summer heat in transit. Liquid starters or fresh natto (when shipped as a starter source) do require cold-pack shipping; expect to pay a premium for that service from suppliers like NYrture. For most home fermenters the powdered form is the practical choice — cheaper to ship, longer to store, easier to dose.