Our mum's spiking another mum's whiskey (4,4)

'whiskey' is the definition.
(I know that sour mash is a type of whiskey)

'our mum's spiking another mum's' is the wordplay.
'mum's' becomes 'ma's' (ma can mean mother).
'spiking' means one lot of letters goes inside another (the word is spiked with inserted letters).
'another mum' becomes 'sh' (both are used to tell someone to be quiet. I am not sure about the 'another' bit.).
'our'+'mas'='ourmas'
'ourmas' inserted within 'sh' is 'SOUR MASH'.