In this activity (on page 2 of the PDF), learners make a plastic protein polymer from milk. Adding vinegar to milk causes the protein casein to solidify or curdle. After allowing the casein to dry, learners can investigate its plastic properties. This activity is a great way to introduce learners to polymer chains, and how they form from individual molecules. Learners can imagine polymer formation by having individual learners link hands to form a line. This is one of three activities in the Take Home guide for the Industrial Chemistry unit in OMSI's Chemistry Lab. Also included in the PDF are: Chalk it up and Shrinkers.