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Cheese from Japan

So (蘇), ancient Japanese concentrated milk蘇

So was cow milk boiled down to about a tenth of its volume and set, a caramel-coloured food with the plain sweetness of milk sugar, made from the Asuka period and paid to the court as tribute. The Heian-period Engishiki rule says boiling 1 to of milk gives 1 shō of so. It is a boundary entry, not a ferment, and the exact old method is not known; today it is made from the texts.

Fully documentedCheese7 h – 8 hFamily: Brunost (brown cheese) / mysost / geitost

Recipe

Amounts from a sourceThe Engishiki rule is 1 to of milk for 1 shō of so, about a tenth. The sources name no other ingredient.
Cow milk1 to (10 shō)Boiled down to give 1 shō of so (Engishiki rule); no other ingredient is named[ndl-crd][yamakawa2016][hirata2023]
Wooden mouldA modern reconstruction pours the thick milk into a wooden mould to set[maff-so]
Starternone; the Engishiki rule only boils the milk down

Total time across the recorded steps: 7 h – 8 h

Start
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What changes: Starting material: fresh cow milk from the court's dairy cattle

Step 1 of 4
Take the cow milk
Time
Not documented
Temperature
Not documented
Salt
None given
Acidity
Not documented

The court's nyūko households kept and milked dairy cattle.

Flavour
Not documented
Texture
Not documented
Colour
Not documented

Microbes at work in this step

Not documented for this step.

Method

Measured measured in a studySet fixed by a specification or tested recipeReported one source reports itTypical a general value, not sourced for this fermentUnconfirmed not yet checked against a source

At a glance

So was cow milk boiled down to about a tenth of its volume and set, a caramel-coloured food with the plain sweetness of milk sugar, made from the Asuka period and paid to the court as tribute. The Heian-period Engishiki rule says boiling 1 to of milk gives 1 shō of so. It is a boundary entry, not a ferment, and the exact old method is not known; today it is made from the texts. Made in 4 steps over 7 h – 8 h. The longest step, boil the milk down, takes 7–8 h (MAFF (Ministry of Agriculture).

Key numbers
Main step7–8 hReported[maff-so]Boil the milk down

What makes this one different

Called an ancient cheese, but the Engishiki rule names only boiling the milk down and no curdling agent. A library survey of the sources gives two views of how so was made, by heat treatment of milk or by processing fermented milk (raku). The Engishiki rule fits the first. The Hirata reconstruction judges heat-concentrated milk to have no model in texts that reached Japan, and found further heating scorched it.

Boundary
Not fermented; the Engishiki method is only boiling milk down
Engishiki rule
1 to of milk boiled down gives 1 shō of so (1 to = 10 shō)

Related ferments

Safety

A historical food known from old texts and modern reconstructions. MAFF says it kept well, so it was used as a restorative medicine [maff-so]. One reconstruction found milk concentrated to 14 % of its weight kept over a year without mould at room temperature.

History and sources

Every number is labelled with how it is known. How this atlas is made

MAFF says milk drinking began in Japan under Emperor Kōtoku (645 to 654), when immigrants presented milk, and that so first appears in records in the Engishiki and the Seiji Yakuryaku, which describe a system of tribute so for the court. Wani, quoted by the library service, dates the first record to the tenth month of 700, when envoys were sent to have so made. A wooden tablet found at the Heijō palace site names "raw so" (3 gō) from Ōmi province. In the Heian period 46 provinces sent so in a set order, the Kuraryō handled it, and it was used at rites such as the Daijin Daikyō feast; it disappeared in the Middle Ages (Yamakawa dictionary). MAFF adds that Fujiwara no Michinaga is said to have taken so with honey when he fell ill at 51. A reconstruction in 1987 at the Asuka Museum of the Nara National Research Institute for Cultural Properties led a Nara farm to sell it.

Microbes
No study we found names its microbes.
Temperature, salt and pH
The sources we found give no temperature, salt or pH figure for any of its steps.
  1. [hirata2023] Hirata M. 2023, So, Buddhism and dairy products (蘇―仏教と乳製品―), Chisei 151:46–51, Obihiro University of Agriculture and Veterinary Medicine repositorypaper
  2. [maff-so] MAFF (Ministry of Agriculture, Forestry and Fisheries), 蘇(そ), Nara Prefecture, にっぽん伝統食図鑑 (Nippon Dentō-shoku Zukan)gov
  3. [ndl-crd] National Diet Library Collaborative Reference Database, case 県立長野-25-147 (Nagano Prefectural Library, created 23 August 2025), 日本古来のチーズのようなもの「蘇(そ)」を食べたい。作り方が載っている資料はあるか。 Quotes the Engishiki (Torao T. ed., 訳注日本史料 延喜式 中, Shueisha 2007, p. 821) and Wani K., in たべもの日本史総覧 (1994, pp. 44–46)gov
  4. [yamakawa2016] 山川 日本史小辞典 (改訂新版), Yamakawa Shuppansha 2016, entry 蘇, as reproduced by Historistbook