Reference point
Open a jar of tương bần and smell from about a hand’s span away.
Do this before you read on. An entry only works when you have just smelled the thing.
Salty, rich, with a roasted note and a deep sweetness at the very bottom. Heavy, slow, and hardly evaporating.
It differs from shrimp paste and fish sauce in its source of protein: the paste is fermented from soybeans and sticky rice, not from animals. So it lacks the fishiness and the ammonia entirely, and has instead a roasted note and the mouldy note of the starter.
This is the base-stage entry of the fermented family, and it shows plant fermentation going in a completely different direction from animal fermentation, even with the same microbial principle.
How to smell it
Put a little soybean paste on a white plate, wait a minute, then smell from a hand’s span away. Then smell fish sauce the same way. What they share is deep umami; what differs is fishy versus roasted.
Why this one is hard
Because it provokes little reaction, so people smell it carelessly. The paste does not shock, and precisely for that reason it demands more attention.
Don’t confuse with
This entry
Fermented soybean paste
Fermented family
Soybean paste is fermented from beans, so it has no fishiness; fish sauce is fermented from fish, so it has clear volatile amines.
This entry
Fermented soybean paste
Fermented family
Both are fermented with moulds, so the difference is not a matter of fungus versus bacteria. Fermented bean curd is matured on tofu, so it is fatty with a clear mouldy note; the paste is fermented on roasted soybeans with rice and then brined for a long time, so it is drier, with a roasted note.
Scientific note
Tương bần is fermented from soybeans and rice with Aspergillus mould. The process produces pyrazines — nitrogen-containing aromatic rings that give roasted, nutty notes. The same group is found in roasted coffee and toasted bread, but here it forms from microbes at ordinary temperature rather than from fire.
2,5-Dimethylpyrazine boils at around 155 degrees, so it is not what makes the paste last. It is marked as leading because it gives the characteristic roasted note, not because it decides the duration.
The paste is placed in the base stage while its pyrazines boil at around 155 degrees and evaporate fairly early. It is the same phenomenon as with fermented bean curd: in fermented foods, the compound you recognise is often light while the body of the smell is heavy.
The pyrazines tell you the beans were roasted before fermenting. What makes the paste rich and lasting is the group of compounds from broken-down soy protein — salty, dense, and mostly too heavy to evaporate. The lasting part belongs to the amino acids and peptides from that breakdown.
In Vietnamese life
Tương bần from Hung Yen has a history of several hundred years and was once offered to the royal court. Paste-making depends on sunshine and on wild yeasts in the air, so each village gives its own profile — much as wine does by region.