Sour oranges or Seville oranges have been appearing in the Korean grocery stores for many years already but I ignored them not knowing they are the sour or bitter or Seville oranges that are best for marmalade. I only found out this variety when I went to visit my daughter in Savannah, GA. She has a "mystery" sour orange tree on her backyard. I brought home 2 fruits when they were still green. I looked online for similar oranges and discovered they are actually Seville/bitter/sour oranges when I sliced the fruits. They have lots and lots of pips which are rich in pectin that helps in the setting/thickening of orange marmalade without store-bought pectin. The sour juice has a very pleasant smell and mild flavor.