shlelf life expiry date

hai mm gurus,

i want to know how the system will pick the shelf life expiry date automatically, for that what settings we have to do (and where).

i have maintained classification (class type) in material type and given expiry date, but while generating GR it was not picking the expiry date(but it is showing shortfall message when we have given below date)

please tell me the procedure,

thanks in advance

subramanyam