What’s in your milk and why permeate is a dirty word

“We only drink milk that doesn’t have any of that permeate stuff you guys add to your milk,” a friend told my husband yesterday.

We don’t add anything to milk. At the farm, milk comes straight from the cows through a cooler into a refrigerated stainless steel vat for collection by the co-op. What happens there is more complex but no more sinister. Basically, fresh milk on Australia’s supermarket shelves has been heated (pasteurised) to make sure any bugs are killed, mixed so the cream doesn’t rise to the top (homogenised) and filtered.

Filtering the milk means you get to choose milk with your favourite protein and fat content – whether that’s skim or milk with an “extra dollop of cream”. It also helps the co-op deal with the natural variation in the protein and fat content of milk over a season. Yesterday, for example, our herd averaged 4.49 per cent butterfat and 3.39 per cent protein whereas, back in October, it got as low as 3.57 per cent butterfat and 3.28 per cent protein.

Dairies have been dealing with this variation in milk production and tastes for hundreds of years by separating cream from milk to make other foods like butter, cream and yoghurt.

So, where does “permeate” come into it? When the milk is filtered to even out fat and protein, the sugars, minerals and vitamins in milk are separated before going back into the milk. Some nerd gave them this ugly name (I think it sounds like plastic) and it’s been used and abused ever since.