익다(ik-da, ikda)
Refers to food or fruit naturally ripening or being cooked thoroughly.
When to use
Natural ripening, Food fully cooked, Fruit ripened, Emotions or experience matured
The nuance
Used when the subject itself changes state naturally or on its own without an active agent.
익히다(ik-hi-da, ikhida)
Indicates an active process where someone causes food to be cooked or someone masters a skill.
When to use
Causing cooking, Skill or knowledge acquisition, Active cooking process, Gaining experience actively
The nuance
Used when an agent actively causes something to ripen, cook, or someone to master a skill.