From a Liquid to a Solid

9 04 2011

It’s no secret that at ACM we love to play with our food. It helps us with build upon our math and science skills. Plus, it is just so much fun!

We have an experiment that will turn one of your favorite beverages into plastic.

All you will need is:

  • 4 ounces of milk
  • 1 teaspoon of vinegar
  • a small pan
  • a small, clean jar

First, you will put the milk in a pan and heat it on the stove until it curdles. This happens when the milk begins to form lumps. Next, you will slowly pour off the runny liquid. Then, put your lumps in the jar and add vinegar. Let it stand for about an hour.

After an hour, you will notice the milk has turned into rubber! Finally, you can shape the lump into a ball or some other simple shape. Be sure to pour out any excess liquid before playing with the rubber. After doing this, let it sit on a paper towel for a few more hours. Once it is completely dry, you will now notice the milk has finally turned into plastic!

You can also paint your new plastic toy like these at Discovery Kids.

How did this experiment work? When milk and an acid (the vinegar) mix together, the milk begins to change properties. The milk begins to separate into a liquid and a solid. The solid material consists of minerals, fat, and a protein called casein. This protein is made of long molecules. Those molecules allow us to bend the lumps like rubber until it hardens and resembles plastic.

Let us know what shapes you managed to create with your milk.

To learn more about proteins and milk or to find new ways to play with your food, visit some of our other experiments.

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11 responses

14 04 2011
Kate

Cool idea. It would be neat to be able to make my own toys. But wait, is this plastic or cheese?

15 04 2011
austinkids

It’s kind of both – it is a polymer made from ingredients used to make cheese. Here’s a good explanation from the Times Online:

You have used the combination of an acid – in this case vinegar, which contains acetic acid – and heat to precipitate casein (a protein) from the milk. Casein is not soluble in an acid environment and so, when the vinegar is added, it appears in the form of globular plastic-like lumps. Casein behaves like the plastics that we see in so many objects around us, such as computer keyboards or phones, because it has a similar molecular form. The plastics in everyday objects are based on long-chain molecules called polymers. These are of high molecular weight and get their strength from the way their billions of interwoven criss-crossing molecules tangle together.

15 04 2011
Kate

I’m going to try this one! Do you think it will work with milk that has passed it’s expiration date? I promise I won’t eat my plastic! I will let you know how it turns out.

15 04 2011
austinkids

I haven’t tried it with expired milk, but I bet that if it’s not too far gone, it should be fine. Milk that is really old starts to separate on its own, so that might be too far gone. Worth a try though, as long as it’s not too stinky!

27 04 2011
Kate

I made the milk plastic and it turned out great! When I heated the milk, it started to form lumps after a while. When I added the vinegar, the lumps really came together. I drained it in a strainer and the solids were pretty crumbly. I kneaded them for a while and that made it feel more rubbery.

Once it felt nice and rubbery, I added food coloring to part of the mixture. It colored the pieces pretty well and I pressed those into dinosaur shaped candy molds. When they were dry I pulled them out and I had made my own dino action figures!

I pressed the rest of the plastic into fruit-shaped molds and let them dry. They were still white when I took them out of the molds so I painted them with acrylic paint.

All in all this was a very fun activity and I ended up with toys that I had made all by myself!

11 10 2011
Holly

I ‘m going to try this tomorrow with my 2 preschoolers.

30 10 2011
jd785

Love this idea and will try it with my students!

9 12 2011
Jessica

I have tried this twice and it isn’t working. What temperature are you heating your milk at? Does it work with whole milk and 2% or a specific milk? Does white vinegar work if it is distilled?

18 01 2012
Teresa Wilson

I found it amusing that this is almost the same recipe I use for ricotta cheese. Check out the sites below. Very good information about the science of cooking.

http://www.seriouseats.com/2010/02/how-to-make-fresh-ricotta-fast-easy-homemade-cheese-the-food-lab.html
http://www.seriouseats.com/recipes/2010/02/how-to-make-fresh-ricotta-fast-easy-homemade-cheese-the-food-lab-recipe.html

14 02 2012
Willoe

This is amazing! Does anyone know if the ‘plastic’ will start to smell/rot? It would be great if they lasted as long…

17 07 2012
Anonymous

Can you heat the milk in the microwave? We can’t use a stove in our classroom.

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