In Yorkshire town, large fruit’s guarantee of freshness? (4-2,4)
I believe the answer is:
sell-by date
'guarantee of freshness?' is the definition.
(something should be fresh on its sell-by date)
'in yorkshire town large fruit's' is the wordplay.
'in' indicates putting letters inside.
'yorkshire town' becomes 'selby' (Selby is a town in North Yorkshire).
'large' becomes 'L' (eg in clothes sizes).
'fruit' becomes 'date' (date is a kind of fruit).
'selby' enclosing 'l' is 'sellby'.
'sellby'+'date'='SELL-BY-DATE'
(Other definitions for sell-by date that I've seen before include "Mark on a perishable" , "Food shop marking" , "Perishable deadline" .)