Plastic Milk

by Deb on October 6, 2011

Milk Plastic

I‘ve been wanting to do this for ages but didn’t think it would be good with the girls because it needs cooking. But now I’ve done it without them a couple of times it’s so simple and I think they’d love it, it will be coming out again.

It’s using just milk and vinegar to make a bio-degradeable plastic. Although it looks similar to cottage cheese it is slightly different – cheese uses rennet to digest and change the casein. I’ve been drying it for a few days and it isn’t oily like old cheese but hard and quite brittle. You can do any amounts, I’ve just used a cup here to try it.


  • About a cup of milk. Most recipes I’ve seen call for full fat, but I did it with skim milk and it worked.
  • 1 Tablespoon of white vinegar.
  • Pot for heating
  • Stirrer
  • Cloth for straining, I used a teatowel.
  • Mould (optional)


  1. Heat the milk until it is simmering. This is the reason I didn’t do it with the girls, although they could do the rest of it quite easily and now I’ll do it with them as a demonstration. Watch until you get the steam and small bubbles but don’t let it boil.
  2. Pour in the vinegar and stir for about a minute. You should see it separate straight away. separating
  3. Strain it through the cloth strainer, you can strain straight into the sink. Be careful in case it is still hot.  draining
  4. Gently squeeze the cloth to get the moisture out. If you are just playing with it get as much out as you can. If you want to mould it into something you need to leave some liquid in or it won’t stick together. done
  5. If you are playing, let it cool and you’re done. Drying time will depend on how thin it is and how much air it gets.

Optional moulding

I used biscuit moulds to make little stars for the girls to paint and play with. It would make good Christmas decorations. I found pressing the curd down into the mould worked the best. Waxed paper would probably have helped but alfoil was ok.


The first attempt. Too thin, and it is easier to pack the casein into the mould than cut it.

If they are too thin and you leave them out to dry they will curl up because they shrink as the water evaporates. My first attempts were about 2 mm and they were too brittle and curly. My second attempt was about double the thickness, then I put a teatowel over them and a weight on them to dry. I’ve been moving the teatowel regularly to help them dry quicker but it’s still taking a couple of days. However, they are nice and flat and much smoother than my original attempt. Hopefully they will be stronger.


The second attempt drying. They are nice and smooth because they had a weight on them, but it is taking a long time to dry.

What’s Happening?

Milk is mostly water with various proteins, sugars, acids and of course fat floating in it. The most common protein is called casein and comes in insoluble microscopic balls. When you add the acid vinegar the casein clumps together into curds and the rest of the liquid is the whey, just like Miss Muffet was eating (although hers wouldn’t have tasted like vinegar).

It’s the tangled clumps of casein that form your plastic. In the 19th and 20th centuries there was much greater use of biological plastics before oil-based plastics became so common. Casein was used in plastic for buttons, as a basis for tempera paint before acrylic, in glue and even for fabrics.

It’s still fun to use for homemade ornaments, buttons, tags or game counters. A mouldable and fun alternative to dough or wood. Now I just need my gorgeous girls to come home so they can paint them.

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{ 4 comments… read them below or add one }

Catherine October 7, 2011 at 6:59 am

Wow! I never knew you could do that. I’m definitely going to try.
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JenT October 9, 2011 at 6:52 am

Neat! I’ve never heard of milk plastic before. Definitely want to try this with my kids!


Susan, the Book Chook October 9, 2011 at 9:31 am

I always learn something from your newsletters, Deb. Thanks for this, and for the explanation of Blood Falls -fascinating!
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Sheryl October 11, 2011 at 12:30 pm

Wow, interesting, I want to try that
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