noun
lye; alkaline water
Specifically the alkaline liquid extracted from ashes, used in traditional cooking or processing.
昔は灰汁を使ってこんにゃくを作った。
In the past, they used lye to make konjac.
noun
harsh taste; bitterness; astringency
Refers to the unpleasant, sharp, or alkaline taste found in certain vegetables (e.g., bamboo shoots, bracken) or poorly prepared food.
たけのこは灰汁が強いので、米ぬかで茹でる。
Bamboo shoots have a strong harsh taste, so you boil them with rice bran.
noun
The froth or impurities that rise to the surface when boiling meat, fish, or vegetables; often skimmed off.
鍋の灰汁を丁寧にすくい取る。
Carefully skim off the scum from the pot.
noun
strong personality; idiosyncrasy; self-assertiveness
Metaphorical extension: a person's rough edges, strong individuality, or excessive self-assertion. Often used in phrases like アクが強い (to have a strong personality) or アクが抜ける (to become mellow). Sometimes incorrectly written as 悪.
See also: アクが強い
彼はアクが強いから、人によって好き嫌いが分かれる。
He has a strong personality, so people either like him or dislike him.
年を取って、だいぶアクが抜けたね。
He's mellowed a lot with age.
Kanji spelling is rare and may not be recognized by all readers; the reading is a gikun/jukujikun.
The origin is uncertain. The kanji 灰汁 literally mean 'ash liquid', reflecting the traditional method of making lye from wood ash. The reading あく is a jukujikun (special kanji reading) assigned to this word.