Bar mostly wrong to offer this form of the grape? (6)
I believe the answer is:
raisin
'form of the grape?' is the definition.
'raisin' can be an answer for 'grape?' (a raisin is a dried grape). I am not certain of the 'form of the' bit.
'bar mostly wrong to offer' is the wordplay.
'mostly' means to remove the first letter (i).
'wrong' indicates anagramming the letters.
'to offer' becomes 'isin' (I can't explain this - if you can you should give a lot more credence to this answer).
'bar' with its first letter taken off is 'ar'.
'ar' anagrammed gives 'ra'.
'ra'+'isin'='RAISIN'
'this' acts as a link.
Can you help me to learn more?
(Other definitions for raisin that I've seen before include "Fruit for the Christmas cake" , "Partially dried grape" , "fruit product" , "A dried grape used in cake" , "Dried fruit" .)