Junket ingredient (6)
I believe the answer is:
rennet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">junket ingredient</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 rennet that I've seen before include "substance used for curdling" , "Substance used to curdle milk for cheese-making" , "Cheese curdling agent" , ""This has turned the milk!"" , "Substance curdling milk in cheese-making" .)