So, what IS permeate?

Today I butted in on a twitter conversation. [View the story “So what is permeate?” on Storify] The question that caught my eye was this:

What is permeate?

I’ve been following the discussion about permeate and I knew that Lynne Strong from Clover Hill Dairies had recently posted something on the subject.

Now my friends who were having the original discussion are not your average consumers. They are scientists! They felt frustrated that they could not find the answers that they were looking for. They could find out that permeate was a natural by-product of milk processing, but could not find out what it actually was.

So I decided to do some research and find out for myself.

I should add that I find the biochemistry of lactation fascinating and I very nearly did my PhD on it. Lactation defines and unites us as mammals on a biological level as well as having a huge social and cultural role in human society. But I digress. Before I talk about the ‘science’ of permeate, I need to describe the chemistry of milk.

What is milk?

Milk is just amazing really. Of course the composition differs with species but essentially milk has the same components: water; proteins; fats and carbohydrates.

Milk proteins include caseins, which are large (in molecular weight) and will become solid in acidic conditions (pH4.6 for cows milk) which is how we make cheese. The proteins which stay in solution during cheese making are called whey proteins (or milk serum proteins) and include lactoglobulin, lactalbumin etc.

There are a number of different types of fats in milk and it varies between and within species. In non-homogenised milk, the fat of milk will eventually float to the surface.

Milk carbohydrates include lactose (milk sugar) but there are other carbohydrates aswell such as glucose and galactose..

Other milk constituents include milk salts (some of which include calcium) that can be bound to proteins or not, cellular metabolites, trace elements (vitamins and minerals) and a few other things.

So what IS permeate?

The diagram in Lynne’s post shows milk entering a factory and some of it going of for cheese making through a process called ultrafiltration. This filtration separates the large proteins (the caseins) and the fats for cheese making and leaves the rest – the permeate. Although whole milk is used in cheese making, adding extra fat and protein makes a better cheese (according to my quick scan of websites etc).

At this point it’s important to remember that permeate is a word meaning stuff that passes through a membrane full of pores, in the same way that filtrate is what passes through a filter. It’s about as meaningful on it’s own as the word ‘leftovers’. It is also why whole milk does not contain permeate, but it does contain all the things that are in permeate.

So what’s in the milk permeate?

This fact sheet from the Dairy Manufacturers Sustainability Council describes ultrafiltration as removing molecules with a molecular weight of 10,000 – 150,000 and a pore size of 0.005-0.1 micrometre. A quick scan for research articles on the composition of milk permeate pulled out this article which states it contains water, lactose, minerals and some nitrogenous compounds (presumably amino acids). The precise composition of milk permeate will vary from factory to factory and season to season, depending on the size of their filters, and the lactose and other content of the milk from the cows supplying the factory.

So what does this all mean?

Lynne has explained what this all means for her dairy and other producers like her in this post. Permeate comes from milk and was added to some milk to standardise it in terms of fat and protein content. While the move to ‘permeate-free’ does mean more whole milk is needed, it also means potentially that a ‘waste’ product from milk production won’t be used. However, while researching for this post I found that groups such as the Dairy Manufacturers Sustainability Council have been promoting ways to remove everything from milk, leaving behind the water that can be used in other processing operations. And that sounds like a good deal to me!


10 thoughts on “So, what IS permeate?

  1. Well done Heather It was a lack of transparency in explaining the “ins and outs” of permeate by processors and industry bodies that has led to all this confusion in the first place and you have done a wonderful job of explaining what they all should have years ago. The question begs to be answered why was it so difficult for them. One just shakes their head in sheer disbelief as all this procrastination has potentially sullied the reputation of natures perfect nutrient cocktail and the cows aren’t happy about this nor am I!

  2. Reblogged this on The Milk Maid Marian and commented:
    Among the most popular posts on Milk Maid Marian are those about permeate, so I thought that, for only the second time, I’d break my “never reblog” rule and highlight this post from science communicator, Heather Bray.

  3. Thanks for this simple explanation seemingly made very complex by milk advertisement that is been shown on Australian TV , ( Farmers pours milk in a glass where milk floats on some liquid inside !)
    For a while I thought that I am sipping chemical called “permeate” !

    I have been trough following stage of my life;
    1) Full cream Milk good for health
    2) Fat free milk is now better for me
    3) May be homogenized, skim milk is best for me
    4) Perhaps Emulsified and cholesterol free milk is strongly recommended….
    After seeing Australian TV advertisement …. I feel red wine is best…

    1. Hi Thomas, no ‘permeate free’ is not ‘lactose free’ because lactose is a normal milk constituent. You can interpret ‘permeate free’ as meaning ‘not watered-down’

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