Gelling agent (6)
I believe the answer is:
pectin
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">gelling agent</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for pectin that I've seen before include "The gel in jam-making" , "Setting agent needed in jams" , "something useful for setting?" , "Jam setter" , "Jelly ingredient" .)