Does the sniff test work for milk and dairy food?

It's not safe to use the sniff test for any food with a use-by date.  The sniff test won't work as you can't smell the bugs that cause food poisoning.

Milk and some other dairy products like yoghurt can have either a use-by date or a best before date.  The manufacturer decides which date marking is the best for the food they produce.  Whether these foods have a use-by or best before date is down to the manufacturer and the way the food is processed.

If a food has a best before date the sniff test can be used - the best before date is about quality, not safety. You can smell food with a best before date to see if it has spoiled.  You can also use visual cues, such as whether you can see mould or if there are any changes to texture.  Food with best before can be eaten after the date on the pack, however they may not taste as good as they did before.

It's always better to check the storage, use-by and best before dates when you buy food so you can help ensure it's safe and to prevent waste.