It isn't easy to make this soup because it takes quite long time, a few days.
I used big iron pot(cauldron) for making this soup.
There are famous brands for iron cookery as likepLodge, Le Creuset, Staub, Skeppshult, Iwaki etc. Eventhough we don't have any worldwide iron cookery brand, Korean has used iron pot - gamasot - from long time ago.
Usually, I use two sort of beef bone, beef leg and other bones.
Before put bone to the pot, it need to dip in cold water for over 1 hour. This step makes getting out blood from bone.
After dipping them in cold water, put them in the pot and boil!
As soon as boiling, drain the water. This step makes getting out blood and foreign substance.
Wash bones with water and put them in pot again and pour water enough.
Make a fire for 5~6 hours until water color turns in white like milk and amount became under half.
Scoop up the white soup and pour clean water again. Make a fire again until white soup and half amount.
Combine 1st soup & 2nd soup in the pot and fire again.
This is last time to fire.
After fire scoop up the all of the soup and cool down soup using refrigerator.
1~2 hours later, you can skim off the fat from soup.
You can enjoy this soup with salt, blackpepper, green onions.
When you preserve this soup, it is good to use zipper bag as below.