In food processing, a large crusher (5)
I believe the answer is:
molar
'crusher' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'in food processing a large' is the wordplay.
'in' means one lot of letters goes inside another.
'food' becomes 'mor' (I can't justify this - if you can you should give a lot more credence to this answer).
'processing' indicates anagramming the letters.
'large' becomes 'L' (eg in clothes sizes).
'a'+'l'='al'
'al' anagrammed gives 'la'.
'mor' placed around 'la' is 'MOLAR'.
Can you help me to learn more?
(Other definitions for molar that I've seen before include "Large tooth" , "Dealing with masses" , "of ivory, perhaps" , "Chewer and grinder" , "Type of tooth" .)