i-adjective
sour; acidic
Describes a sharp, acidic taste like that of lemons, vinegar, or unripe fruit. Can also be used figuratively for a sour expression or mood.
このレモンはとても酸っぱい。
This lemon is very sour.
酸っぱいものが苦手です。
I don't like sour things.
Standard kanji-kana spelling; the kanji 酸 means 'acid'.
Kana spelling is common in casual writing and for emphasis.
From the adjective stem 酸 (su, 'sourness') + っぱい (-ppai), an emphatic suffix. The kanji 酸 is used for its meaning 'acid'.