大黄豆淘净，煮极烂，用竹筛捞起。将豆汁用净盆滤下，和盐留好。豆用布袋或竹器盛之，覆於草内。春暖三四日即成，冬寒五六日亦成，惟夏日不宜。每将成时，必发热起丝，即之去覆草，加捣碎生姜及压细之盐，和豆拌之，然须略咸方能耐久。拌后盛坛内，十余日即可食。

Wash soybeans clean and boil until extremely soft. Use a bamboo strainer to fish them out and mix with salt. Place the beans inside a cloth bag or bamboo container and cover with grass. In warm spring season, they will be ready after 3 or 4 days. In cold winter, it will take 5 or 6. Hot summer will not work for this. It is ready when the mash gives off heat and makes threads (when you pull it apart). Mix in mashed ginger and finely crushed salt in order to keep it from going bad. When it is mixed, place inside a fermenting jar. It will be ready to eat after ten days or more. These are equally good with fried or steamed meat.

— 中馈录 Zhongkuilu, 13-14th century

I know of two ways to (intentionally) grow mold in beans. The first is to use a mix in a bit of a finished product as a starter. Mix in natto, and you get natto. Mix in tempeh, and you get tempeh. The second way is to coat the cooked and semi-dried beans in flour and leave them outside. That is how you get the meidou used as a starter for Chinese bean pastes.

So which one is this? Well, we have no starter, but we do know it’s aged in an oxygenated environment. The threads sound like natto, which is made covered. We don’t know what kind of grass is used to cover the beans, so I doubt that’s meant to be the source of the mold. So nope, I have no idea what’s going on here. Let’s just try it and see what happens.

I soaked and boiled soybeans, let them cool, mixed in salt and wrapped everything in a clean cotton cloth. Since I had no grass lying around, I just wrapped the whole thing in a banana leaf, making sure to keep it loose enough for air flow. As a control, I also made a batch of tempeh using the packaged mould starter used for making laozao.

After 6 days, I unwrapped both. The tempeh beans were covered in a white mold similar to natto. My luck-of-the-draw beans weren’t too shabby either, in that they were definitely moldy. Blue, black, white, all kinds of action going on here.

I added enough salt to approximate the saltiness of soy sauce, and enough crushed ginger to remoisten the mix, and then from there into a sealed jar.

See you in ten days!