The appearance is not very nice, but these are the "pearl kan" that I took from home. They are also called "sour pomelo."
Wash the pearl kan and peel the skin off in 4-6 sections.
Weigh just the skins. I had 294 g of skins so now you can prepare the same amount of water and sugar (300 g) needed to boil in Step 8.
Fill a pot that can withstand strong acidity, such as enamel, with lots of water, and boil the skins.
Once the skins have been soaked completely in the boiling water, cover with a plate and simmer for 15 minutes.
Dump out the water and repeat Steps 4-6 one more time.
Gently use a knife to scrape off the outside skin. Soak in water overnight. Wash in water while replacing with clean water occasionally.
Place the peels in a pot and cover with 1/3 of the sugar and water. Let simmer on medium heat for 10 minutes.
Add another 1/3 of the sugar and simmer for 10 more minutes. If there is still a lot of water at this point, remove the skins and let it boil down about halfway.
Add the remaining 1/3 of sugar and return the peels to the pot. Simmer for 15 minutes. When the liquid has lessened, shake the pot so that they don't burn.
Place the peels and liquid into a dish that has been sterilized by boiling and store in the refrigerator. If it has boiled down thoroughly, it will keep for 3 months.
Story Behind this Recipe
Even without doing anything to take care of it, the tree in our backyard produces lots of pesticide-free pearl kan fruits. Since they are completely organic, the skins can be used practically.
I learned this from my mother who used to boil yuzu peels and deliver them around the neighborhood.
If you use a citrus fruit that has a hard skin with a thick white part (such as oranges, mandarin oranges, yuzu, pomelo, etc), you can make this following the same procedure. Since citrus fruits that have a thick white section absorb lots of water when soaked, pay attention to their condition and adjust the amount of water as necessary.