Wash the chestnuts and drain into a colander. See Recipe ID: 2370874 and Recipe ID: 1988328 for instructions on how to peel the outer shells.
Put the chestnuts in water as soon as they're peeled. When all the chestnuts are peeled, drain into a colander.
Put the peeled chestnuts in an enamelled pan and add in enough water to cover them up (the water is not listed in the ingredients), add the ● bicarbonate of soda and bring to a boil. Lower the heat and simmer gently for about 20 minutes until the water is reddish-black.
Move the pot to the sink and run cold water into it from the tap to lower the temperature of the water in the pan and remove the scum.
Rub the fibers off the surface of the chestnuts with your hands, and soak in plenty of water. Soak the chestnuts for several hours while changing the water many times. Drain into a colander.
Wash out the pot and add the chestnuts with enough water to cover them (the water is not listed in the ingredients) plus the ○ bicarbonate of soda, and repeat Step 3. Poke a chestnut with a skewer or toothpick to see if it's tender.
Repeat Steps 4 and 5, remove all the fibers from the chestnuts, and try eating one. If it's still bitter, simmer again in water without any bicarbonate of soda added, then repeat Step 5.
Put the pre-boiled chestnuts and water to cover in the pot and bring to a boil. Add the sugar. Skim off the scum. You can add half the sugar in the first round, and the rest in the second round.
Put a piece of aluminium foil or kitchen parchment paper right on top of the simmering chestnuts in the pot to act as an otoshibuta (dropped lid). Lower the heat and simmer for 15 to 20 minutes.
Leave the pot until the simmering liquid has cooled. Repeat Steps 9 and 10 two more times. After the last time, remove the foil or pepper and leave to rest in the refrigerator overnight.
To store for a short period, pack the chestnuts in sterilized jars. Sterilize and dry the jars just before you need them.
Fill the jars 70% full with the chestnuts in syrup, so that the chestnuts are immersed in syrup.
To vacuum pack the jars: line the bottom of a pot with a kitchen towel and add water. Put in the filled jars, and just put the lids on top. Leave the jars to cook in the water for 15 minutes or so after the water starts to steam. Close the lids quickly.
To keep the chestnuts for a longer time, use sterilized containers (pour boiling water into freezer-safe storage containers and dry). Put the chestnuts and syrup in the containers and close the lids, and store them in the freezer. You can keep the chestnuts for about a year this way.
It's best to label the jars or storage containers.
Story Behind this Recipe
This year, I had opportunities to make chestnuts cooked in their inner skins in syrup several times. It takes a lot of time and effort, so if the results are not what you want them to be it's very disappointing. I thought I'd put all the key points I've noticed in one place.
The water to vacuum pack the jars in Step 13 should come more than halfway up the sides of the jars, but lower than the shoulders. I tried some of the chestnuts in their inner skins I made last fall and stored in the freezer this September, and although they were a bit soft, the flavor was just as good. If you like, add a little soy sauce or salt in Step 10 (in the 3rd round).