Thua nao vs Douchi
The short answer
Both are fermented soybeans used as seasoning, and they are made in opposite ways. Thua nao is boiled soybeans left for a few days to bacteria of the genus Bacillus, with no salt; it turns alkaline, smells of ammonia, and keeps only if it is dried. Most douchi is grown over with mould, then salted and aged for months, and it is the salt that keeps it. Thua nao is mashed and dried in thin discs that are toasted before use; douchi stays as whole salted beans. Neither is a stand-in for the other in anything read here.
Side by side
| Thua nao | Douchi | |
|---|---|---|
| Botanical identity | Glycine max (L.) Merr. | Glycine max (L.) Merr. |
| Part used | seed | seed |
| Origin | Not established | China. The studies describe douchi as a traditional Chinese fermented soybean product; the soybean itself was domesticated in the eastern half of north China, according to the handbook account of the plant. |
| Flavour notes | savoury, pungent, nutty, bitter | savoury, salty, smoky, nutty |
| Heat | Scoville does not apply | Scoville does not apply |
| Flavour | Savoury, with some bitterness, and not salty: it is made without salt, which the papers contrast with shrimp paste. A study read in abstract found both a starter-made and a naturally fermented thua nao far richer in free amino acids than the cooked beans, and attributed the bitterness mainly to the hydrophobic and basic amino acids and the savouriness mainly to the acidic ones. | Savoury and salty, with some bitterness. In seven douchi from Sichuan and Chongqing glutamic acid was the most abundant free amino acid, followed by aspartic acid, and the amino acids that taste bitter were together the largest group, which the authors say matched their tasting. |
| Aroma | Strong, and described by those who study it in blunt terms. A review calls the ripe beans strongly ammonia-like and compares the traditional product to fish sauce; one group writes of a strong meaty aroma, another of a smell often described as pungent or rotten. The name carries the same idea: the review glosses thua as soybean and nao as spoiled. The dried disc smells different. In discs made in one laboratory the compounds that counted most towards the smell were grouped as green and fatty, nutty and roasted, sweet, sulphurous, woody and smoky, sour and fermented, and floral. | Asked which words applied to three douchi, a hundred consumers used sauce-like, smoky, nutty, roast, caramel and flower for what they liked, and sour, beany, sulphur and alcohol for what they did not. The types differ. Liuyang douchi was the smokiest, which the authors put down to guaiacol; Yangjiang douchi was more sour and nutty; Pingjiang douchi, aged for a year, held the most volatile compounds and scored on every note. A separate study of seven douchi from Sichuan and Chongqing found no volatile compound common to all seven. |