Grammar fix
be off
(food) has gone bad
if milk or other food is off, it has gone sour or bad and no longer tastes or smells right
expressionB1common
Hear it in context
Notice where the phrase sounds natural.
I think this milk's off — it smells a bit funny.
Give the cream a sniff; I reckon it's a bit off.
Fix the pattern
One small grammar move makes it sound right.