Tamba black soybeans: characteristics and product information
| Origin | Oji district, Kasuga, Tamba City, Hyogo, Japan |
|---|---|
| Crop | Tamba black soybeans (Tamba kurodaizu) |
| Seed origins | Seed shared by a local farmer, continued through our own seed saving |
| Characteristics | Large, deep-black beans with a plump texture when cooked |
| Flavour | Rich bean flavour, soft yet with a pleasing bite |
| Suggested dishes | Sweet simmered black beans, New Year dishes, black soybean rice, Japanese sweets, baking and desserts |
| Sowing | Usually late June–early July; raised in seed trays before transplanting |
| Growing | About 30–40 cm between plants; rotation, grass mulch, minimal soil disturbance and string supports |
| Harvest | Judged by full maturity and dryness of pods and beans, varying by year |
| Drying and processing | Whole plants naturally dried; hand shelled, cleaned and sorted; moisture checked before packing |
| Form sold | Dried black soybeans only. We do not sell edamame. |
| Start of sales | After drying and sorting; sometimes in the New Year rather than before year-end |
| Growing approach | Grown without synthetic pesticides or chemical fertilisers. We do not hold Organic JAS certification. |
We distinguish general descriptions of Tamba black soybeans from our own experience. Harvest dates and availability vary by year.
Purchase and availability enquiries
For households, confectioners, restaurants and shops, tell us your quantities and timing. We prioritise full maturity, drying and sorting, so the new crop may not be ready until after New Year.
Registering interest is free, with no obligation to buy and no guarantee of stock. Orders are confirmed only after you agree to quantities, prices and delivery arrangements.
How we came to grow Tamba black soybeans
Tamba black soybeans, also called Tamba kurodaizu, are among Japan’s best-known premium black soybeans. Their large size, beautiful black colour, plump cooked texture and rich flavour are prized, particularly in kuromame-ni, the sweet simmered beans served in New Year osechi food.
As with Tamba Dainagon azuki, we began growing them through a neighbouring farmer. Soon after we moved to Kasuga, Tamba City, he shared seed from his own Tamba black soybeans. We have grown from that seed ever since, keeping some of each harvest for the following year.
Local seed, grown in our fields and carried into another year: that simple story is part of what these beans mean to us.
Why Tamba black soybeans are special
Tamba black soybeans are known for being larger than ordinary soybeans. Hyogo Prefecture’s materials give examples of around 80–90 g per 100 Tamba black soybeans, compared with roughly 30 g for ordinary soybeans. These are representative figures for the variety group, not measurements of our harvest.
Their glossy black skin, plump shape after simmering and soft yet substantial texture have long been valued in cooking and confectionery.
Their history is closely linked to the old province of Tamba, particularly around present-day Tamba-Sasayama. Local lines and growing traditions in places such as Kawakita and Habe helped build their reputation over many years. Our fields are not at a claimed birthplace, but in Oji, Kasuga, Tamba City, within the same Tamba region.
The name Tamba kurodaizu covers several regional lines and selected varieties. We have not yet verified the precise variety or lineage of the seeds shared by our neighbour.
Building soil without repeatedly disrupting it
We rotate black soybeans, azuki, chillies and vegetables between fields. A foundation of our approach is to preserve soil structure as far as possible, rather than repeatedly cultivate it heavily.
Microorganisms, fungi and earthworms live in a complex environment alongside plant roots. Intensive tillage can disturb soil aggregates and habitats. Its effects nevertheless vary with soil type and management: not every form of cultivation is uniformly harmful.
We would rather avoid the equivalent of demolishing a town’s buildings and roads and rebuilding them every year. Instead, we gradually build soil using compost, grass and straw organic matter, mulch, rotations and living roots.
We do not use synthetic pesticides or chemical fertilisers on our black soybeans. For details, see How we grow (Japanese).
Giving dried beans room to grow
We leave around 30–40 cm between plants to allow airflow, light into the foliage and room for branches.
Denser planting can increase yield per unit area. We choose a roomier arrangement that makes each plant’s growth and pod filling easier to observe. We are not claiming that wider spacing always increases yield or quality per unit area.
What we grow and sell is fully maturedried black soybeans. Our work from growing through harvest is aimed at large, well-filled beans.
Protecting seedlings from birds, planting with the season
We often direct-sow azuki, but usually raise black soybeans in seed trays before transplanting. The seeds and emerging shoots are very attractive food for local birds.
Moving them to the field once established reduces damage just after germination. We usually sow in late June or early July, a little earlier than azuki.
We do not fix the same date every year. Temperature, rain, soil condition and the progress of summer all matter. Soybeans also respond to day length, so warmth alone cannot determine changes in timing. We consider both the calendar and the actual field.
Supporting plants without earthing up
Soybeans are often earthed up, with soil drawn around their bases. We value keeping living roots and vegetation even in our paths.
Moving large amounts of soil to the plants does not fit that approach. We also avoid replacing the soil with heaps of nutrient-rich compost: under some conditions excess nitrogen can encourage foliage at the expense of balanced pod development.
Instead, we make small planting holes that position the base a little deeper, then use string supports as plants grow to prevent lodging. We provide support while leaving surrounding soil as undisturbed as possible.
Mountain water for flowering and pod growth
Moisture management is particularly important during flowering, pod formation and the start of bean filling.
Piped water from a mountain stream lets us irrigate when needed rather than rely solely on rain.
We aim to keep moisture available to roots consistently, without excessive drying or waterlogging, adjusting according to the soil and the plants.
Watching insects and removing them by hand when needed
As on azuki, leaf-eating caterpillars appear on black soybeans. We begin by observing the plants and the extent of feeding damage.
When necessary, we catch and remove them by hand. Our chickens sometimes enjoy the captured caterpillars.
We may remove badly damaged leaves, while avoiding taking too much foliage needed for photosynthesis. The aim is not a complete absence of pests, but healthy plants able to grow through some feeding damage.
Harvesting fully mature black soybeans
Tamba black soybeans are also popular as autumn black edamame, harvested in their pods while immature. We do not sell edamame: our product is fully mature, dried black soybeans.
We leave the plants in the field beyond the edamame stage until the beans fully mature.
Dry azuki pods can split and shed their beans. In our experience, black soybean pods tend to remain more firmly closed, making drying on the plant easier.
There is no fixed harvest date. Once leaves fall and pods darken, harden and dry, we check the beans themselves. The deciding factor is not the calendar buthow the beans inside the pods have developed.
Natural drying, shelling and hand sorting
We cut fully mature plants at the base. In suitable weather, they may spend a while leaning against a fence to dry, before we bring them into the barn and hang them for further drying.
Dry pods are spread on straw mats or similar surfaces and beaten open. We remove pod fragments and debris, sort the beans by hand, then inspect them again after cleaning.
We do not judge dryness by appearance alone. We also use a grain-and-bean moisture meter to check suitability for packing. Finished beans are packed with a pulse vacuum sealer, and we aim to sell each harvest before the next one.
None of these steps is glamorous, but they take time and work. What matters to us is not hurrying past them.
Slow drying and our thoughts on flavour
We prefer gradual drying while observing condition rather than drying beans abruptly. In comparisons with shop-bought beans, we have liked the shape and texture of ours. Customers have also given favourable comments on flavour and texture.
That does not scientifically prove natural drying superior to all machine drying. Quality depends on variety, maturity, drying speed, temperature, moisture, storage, cooking and other factors. Natural drying can also damage quality during persistent humidity or bad weather.
We choose slow drying as a method we can observe closely and use to achieve a finish we are happy with.
Sometimes they are not ready for New Year
Demand peaks at year-end. But full maturity, natural drying, shelling, sorting and packing can mean that sales of the new crop begin after New Year.
Not all beans sold before New Year are machine dried, and machine drying does not necessarily harm quality. Even so, we prefer to check the finish before delivering rather than rush to meet a sales date.
From New Year food to sweets
Sweet simmered black soybeans in osechi are perhaps their most familiar use. The large beans become plump and glossy after gently absorbing the sweet cooking liquid.
They also suit black soybean rice, Japanese sweets, baking and creamy desserts.
Our customers use them not only for New Year dishes but also for sweets and desserts. Many look forward to them each year, and regular customers’ expressions of interest can account for a substantial part of the harvest. That is deeply encouraging for us as growers.
Seed for next year, and what we aim for
We also keep harvested beans for next year’s seed. These are not leftovers: we choose well-filled beans with good size and shape after sorting.
We estimate the weight to save from next year’s planting requirements, using measures such as thousand-seed weight. Choosing good-looking beans alone does not guarantee genetic improvement, but securing good seed and observing the next crop matter to us.
The seed shared by our neighbour still grows in our fields, carrying into another season. Tamba black soybeans remind us of the connections between land and people.
We look beyond yield alone, care for the soil, observe individual plants and finish the beans carefully after full maturity. Each small bag holds a year of that work.
Purchase and business enquiries
We welcome interest in the next harvest throughout the year. Tell us quantity, use, timing and delivery municipality. Households, confectioners, restaurants and retailers are welcome to enquire.
After harvest, drying and sorting, we explain quantities, prices, the total including delivery and delivery arrangements. If stock is already available, we explain the current offer. An order is confirmed only after you agree.
The new crop may not go on sale until after New Year. If you need beans for a particular date, such as the New Year holidays, please mention it when enquiring.
Registration is free, with no obligation to buy and no guarantee of stock or fixed quantities. See the linked page for seasonal local delivery and shipping within Japan.
Current products can also be found in our Mercari listings. Please complete Mercari purchases within Mercari.
Frequently asked questions
Common questions about growing, cooking and buying our beans.
What are Tamba black soybeans?
Also called Tamba kurodaizu, they are large, highly regarded black soybeans long grown in Tamba, used in dishes such as simmered beans.
Why are they considered a premium food?
Their size, glossy colour, cooked texture and attractive shape, along with a long-standing culinary reputation.
How large are they compared with ordinary soybeans?
Hyogo materials give representative examples of around 80–90 g per 100 beans, compared with about 30 g for ordinary soybeans. These are not measurements of our harvest.
Where did they originate?
The old Tamba province, particularly areas such as Kawakita around present-day Tamba-Sasayama, is known for their historical cultivation. Some details of the exact origin remain uncertain.
Where do you grow them?
In Oji, Kasuga, Tamba City, Hyogo, using seed originally shared by a local farmer.
Do you also sell black edamame?
No. We sell fully mature, dried black soybeans, not the immature beans harvested as edamame.
When do you sow and harvest?
Usually we sow in late June–early July. Harvest is guided by maturity and dryness of pods and beans rather than the calendar. Sales begin after drying and sorting.
Why raise seedlings first?
Birds readily eat the seeds and shoots, so we raise them in trays and transplant once they have grown stronger.
Why do you not earth up?
To avoid heavily disturbing soil and living roots. We plant a little deeper and support with strings.
Do you use pesticides or chemical fertilisers?
We use no synthetic pesticides or chemical fertilisers on our black soybeans and do not hold Organic JAS certification. Read more in How we grow (Japanese).
How are they dried and sorted?
We gradually dry plants and pods under natural conditions, then shell, clean and sort by hand. A moisture meter helps check condition before packing.
Is natural drying better than machine drying?
We prefer it and are happy with the result. Quality depends on many conditions, though, and we cannot say that natural drying is always superior.
Why might the new crop miss New Year?
We prioritise full maturity, natural drying and hand sorting, so sales may begin after New Year. Please enquire ahead if your timing is fixed.
How should I store them?
Follow the product label. Keep in a cool, dark place away from direct sunlight, heat and humidity. After opening, use an airtight container to exclude moisture and insects, and use promptly.
Can I register interest in the next harvest?
Yes. Please use the purchase enquiries page. Registration is free and carries no obligation or guarantee of stock. We will explain quantities and prices after harvesting, drying and sorting.
Do you save your own seed?
Yes. After sorting, we reserve well-filled beans with good size and shape, using measures such as thousand-seed weight to estimate the amount needed.
References
Sources on Tamba black soybean history and general characteristics, distinguished from our own growing and tasting experience.