Lumps in milk that aren’t due to curdling are likely the cream component of the milk separating from the milk, which happens when the milk isn’t homogenised.

Homogenisation refers to a process where fat globules in milk are passed through a high-pressure machine to break them up into smaller droplets. This results in a more uniform milk product, with a more consistent and full-bodied flavour and colour. Unlike pasteurisation, which is required by Australian law to make sure any unwanted bacteria in milk are killed off, homogenisation is optional in the milk making process.  

What that means for you: If you buy non-homogenised milk, the fat portion or cream of the milk may separate from the liquid component and may result in lumps when the milk hasn’t actually curdled.