How to Ferment Natto

A Step-by-Step Guide for Homemade Probiotics

Fermenting natto at home is a process that involves cultivating beneficial bacteria on soybeans to produce this traditional Japanese food. (What wine goes well with Japanese food?) Renowned for its distinctive flavor, stringy texture, and health benefits like a high content of vitamin K2 and nattokinase, natto has been a staple in Japanese diets for centuries. The fermentation is typically achieved by adding natto starter spores to cooked soybeans and maintaining the culture at a consistent temperature, allowing the bacteria Bacillus subtilis to thrive and ferment the beans.

The key to successful natto fermentation lies in preparation and sanitation. Before introducing the natto starter, soybeans must be thoroughly washed and cooked until tender. Utensils and containers used in the process need to be sterilized, often by pouring boiling water over them, to prevent unwanted bacteria from interfering with the fermentation. Once mixed with the starter spores, the beans are kept in a warm place, often in a specialized natto incubator or a warm kitchen area, to facilitate the fermentation process.

Maintaining the correct temperature and environmental conditions is crucial for cultivating the natto culture. Although the precise temperature can vary, it is generally understood that a steady warmth around 40°C (104°F) is ideal for the bacteria to activate and ferment the beans. After an incubation period, which can vary according to desired taste and texture, natto is ready to be enjoyed or refrigerated for later use.

Understanding Natto

Natto is a traditional Japanese ferment made from soybeans. These beans undergo a fermentation process using Bacillus subtilis, a specific type of bacteria. This process transforms the beans into a sticky, stringy delicacy with a distinctive strong flavor and smell. Consumed as a breakfast staple in Japan, natto plays an important role in the Japanese diet.

Fermentation Process:

• Soaking: Soybeans are initially soaked in water to equally hydrate.

• Steaming: Post hydration, the beans are steamed until soft.

• Inoculating: While still warm, the beans are inoculated with B. subtilis spores.

• Incubating: The inoculated beans are kept at about 40°C for 18-24 hours to ferment.

• Aging: Natto is then refrigerated to develop flavor over several days.

Natto is considered a superfood owing to its rich probiotic content that can enhance gut health. It offers numerous health benefits, such as aiding in heart health by reducing cholesterol levels and promoting bone health through its high vitamin K2 content. Additionally, natto provides a savory umami taste to various dishes.

While its pungent aroma and texture may be an acquired taste, fans of natto value it for its nutritional profile and unique culinary contribution. As a fermented soybean product, it embodies the benefits of fermentation—a method heralding not only preservation but also the enhancement of food.

Ingredients and Equipment

Ingredients:

• Organic Soybeans: The base for making natto is organic soybeans, which may have a higher content of vitamin K2 after fermentation.

• Water: Purified or filtered water is necessary for soaking and cooking the soybeans.

• Natto Starter: A quality natto starter or spore powder is essential for inoculating the soybeans with Bacillus subtilis to initiate fermentation.

Equipment:

• Pressure Cooker or Pot: A pressure cooker is recommended for cooking soybeans faster and evenly, but a regular pot can also be used.

• Stainless Steel Colander or Strainer: Needed to drain the cooked soybeans.

• Utensils (Spoons, Measuring Cups): Sterile utensils help prevent undesirable bacteria from contaminating your natto.

• Fermentation Containers: Shallow containers, ideally with a large surface area, facilitate even fermentation.

• Sanitization Supplies: Use boiling water or sterilization solutions to ensure all equipment is free from harmful bacteria.

• Incubation Equipment: This can be an oven with a reliable low-temperature setting, a dehydrator, or a yogurt maker to maintain the right environment for fermentation.

For serving, rice, soy sauce, mustard, and sesame oil can be paired with the natto for additional flavor. During the fermentation process, natto powder can be used as a starter and is a carrier for vitamin K2, a nutrient linked to reducing the risk of heart disease.

Throughout the process, containers should be covered with aluminum foil or a cloth then secured with a plastic film to create the necessary conditions for Bacillus subtilis activity. Maintaining sterile conditions and using the correct equipment ensures successful fermentation and the production of high-quality natto.

Preparation Process

The preparation process for making natto involves careful selection of soybeans, proper soaking and cooking, and controlling the environment for the natto culture. Precision in temperature and handling ensures successful fermentation.

Selecting Soybeans

Choose organic soybeans for their quality and health benefits. Inspect the beans and rinse thoroughly to remove any debris. Discard any discolored or damaged beans.

Soaking and Cooking

Soak the soybeans in cold water for 9 to 12 hours to ensure even hydration. After soaking, cook the beans until tender. This can be done in a large pot or a pressure cooker. In a pot, boil for about 6 hours; in a pressure cooker, cook for 45 minutes to an hour.

Creating the Culture Environment

After cooking, rinse the boiled soybeans in cold water to cool them down. Then, sterilize all utensils and containers to be used to avoid contaminating the culture. This creates a safe environment for the bacillus subtilis bacteria.

Fermenting the Soybeans

Mix the soybeans with natto spores or commercial natto as a starter culture. Use a non-reactive pot to prevent metal flavors, or place them into sterilized containers for incubation.

After Fermentation

Once the fermentation process is complete, which typically takes 20-24 hours at an incubation temperature of about 100°F (40°C), chill the natto in a refrigerator to halt the fermentation. Post-fermentation, natto develops its characteristic slimy texture and strong odor.

Finishing and Storage

Proper finishing touches and storage of natto are crucial to maintain its flavor and probiotic properties. Attention to detail during these final steps ensures that the homemade natto retains its quality and traditional Japanese character.

Final Touches

Once fermentation is complete, the natto should exhibit a distinct sticky texture and a characteristic smell, hallmarks of successful fermentation by Bacillus subtilis. It is common to enhance natto before consumption with condiments such as soy sauce, mustard (preferably Japanese mustard), sesame oil, or even a sprinkle of rice. These additions should be measured and added according to personal taste, keeping in mind the dominant flavors of the natto.

Storing Natto

Proper storage is crucial to ensure the longevity and safety of natto. Containers for natto should be airtight and can be lined with aluminum foil for extra protection. To store natto, one should adhere to the following guidelines:

• Refrigerator (Short-Term): Store natto in the refrigerator for up to one week to maintain the best flavor and texture. Use a temperature setting that is consistent and cold enough to preserve the natto's probiotic qualities that can aid in digestive health and potentially reduce the risk of heart disease.

• Freezer (Long-Term): For extended storage, natto can be kept in the freezer. When stored in an airtight container, natto can last for several months. Thawing should be done in the refrigerator to ensure gradual temperature change and preservation of the beneficial properties.

By using the correct equipment and following these storage guidelines, one can make natto at home that rivals those found in an Asian grocery store. The final product will furnish a reservoir of probiotics and a slice of traditional Japanese ferment at your fingertips.