Effervescent powder (7)
I believe the answer is:
sherbet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">effervescent powder</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for sherbet that I've seen before include "Australian beer" , "Sweet fizzy powder" , "Foreign beer" , "Fizzy stuff" , "A fizzy drink, a fruit drink" .)