Try gin and it mixed by tenor: extremely tasty substance? (5-6)
I believe the answer is:
nitty-gritty
'substance?' is the definition.
(I know that center can be written as nitty-gritty)
'try gin and it mixed by tenor extremely tasty' is the wordplay.
'and' means one lot of letters go next to another.
'mixed' is an anagram indicator.
'by tenor' becomes 't' (I am not sure about the 'by' bit.).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'tasty' with its centre taken out is 'ty'.
'try'+'gin'='trygin'
'trygin' after 'it' is 'ittrygin'.
'ittrygin' with letters rearranged gives 'nittygri'.
'nittygri'+'t'+'ty'='NITTY-GRITTY'
(Other definitions for nitty-gritty that I've seen before include "Essential details of a matter" , "Essential aspects" , "Most important details (of a matter)" , "Brass tacks" , "Essence" .)