How to Make Non-Toxic Glue From Milk

Use common kitchen materials to make your own glue. Add vinegar to milk, separate the curds, and add baking soda and water. Voila, you've got glue!

• Difficulty: Average
• Time required: 15 minutes

Materials

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5 Ways to Make Glue

By Anne Marie Helmenstine, Ph.D.

• 1/4 cup hot water
• 1 tbsp vinegar
• 2 tbsp powdered dry milk
• 1/2 tsp baking soda
• Water

How to Make It

1. Mix 1/4 cup hot tap water with 2 tbsp powdered milk. Stir until dissolved.
2. Stir 1 tbsp of vinegar into the mixture. The milk will begin to separate into solid curds and watery whey. Continue stirring until the milk is well-separated.
3. Pour the curds and whey into a coffee filter positioned over a cup. Slowly lift the filter, draining the whey. Keep the curd, which is in the filter.
4. Squeeze the filter to remove as much liquid as possible from the curd. Discard the whey (i.e., pour it down a drain) and return the curd to a cup.
5. Use a spoon to break the curd into small pieces.
6. Add 1 tsp hot water and 1/8 to 1/4 tsp baking soda to the chopped curd. Some foaming may occur (carbon dioxide gas from the reaction of baking soda with vinegar).
7. Mix thoroughly until the glue becomes smooth and more liquid. If the mixture is too thick, add a bit more water. If the glue is too lumpy, add more baking soda.
8. The finished glue can vary in consistency from a thick liquid to a thick paste, depending on how much water has been added, how much curd was present, and how much baking soda was added.
9. Use your glue as you would any school paste. Have fun!
10. When not in use, cover your cup of glue with plastic wrap. Over time, its consistency will become smoother and more clear.
11. Unrefrigerated glue will 'spoil' after 24 to 48 hours. Discard the glue when it develops a spoiled milk smell.

Tips for Success

• The separation of curds and whey works best when the milk is warm or hot. This is why powdered milk is recommended for this project.
• If the separation doesn't work well, heat the milk or add a bit more vinegar. If it still doesn't work, start again with warmer water.
• Clean dried glue by loosening/dissolving it in warm water and wiping it away. Glue will wash out of clothes and off surfaces.

Reaction Between Milk and Vinegar

Mixing milk and vinegar (weak acetic acid) produces a chemical reaction that forms a polymer called casein. Casein is essentially a natural plastic. The casein molecule is long and pliable, which makes it perfect for forming a flexible bond between two surfaces. The casein curds may be molded and dried to form hard objects that are sometimes called milk pearls.

When a small amount of baking soda is added to chopped curd, the baking soda (base) and residual vinegar (acid) participate in an acid-base chemical reaction to produce carbon dioxide, water, and sodium acetate. The carbon dioxide bubbles escape, while the sodium acetate solution combines with the casein curds to form a sticky glue. The thickness of the glue depends on the amount of water present, so it can be either a sticky paste (minimal water) or a thin glue (more water).