also: ふすべる
Standard kanji spelling for the reading くすべる.
Alternate reading ふすべる, less common than くすべる.
Kana spelling is practical when the kanji is difficult or uncommon.
燻す (いぶす) also means to smoke or fumigate, but is a godan verb and often implies a lighter or more indirect smoking, while 燻べる is ichidan and can suggest a more direct exposure to smoke.
燻製 (くんせい) is a noun meaning smoked food or the process of smoking, whereas 燻べる is the verb for the action of smoking something.
The verb 燻べる is derived from the noun 燻 (くすべ, 'smoke') and the verb suffix る. The kanji 燻 means 'smoke' or 'fumigate'. The alternate reading ふすべる is a variation, possibly influenced by the verb 燻す (ふすぶ).