It needs hint of lime when served up (5)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A clue-as-definition: SA (sex appeal – ‘it’) L (first letter or ‘hint’ of lime) + a reversal (‘served up’) of AS (when) – Joyce is keen to stress that salsa does not need a hint of lime when served up! The acidity you need can come from adding lemon or vinegar.