When you are talking about cookin you shold use "금방"(quickly) instead of "잘" (well) "이 음식은 금방 익어요" opp: "이 음식은 익는데 오래 걸려요" (it takes long) When it comes to adjective however, it's "잘 익은" vs "설익은" "잘 익은 음식" (well done) "설익은 음식" (half done) Additionally, "익다" also means "to ripen", "to grow" example: "가을 들판에 곡식이 익는다" "포도가 잘 익었다" We also have special nouns dedicated to "unripe fruit, just edible" 풋과일: unripe fruit (edible nevertheless) 풋사과: unripe apple (edible nevertheless)

이 음식은 잘 안익어요.