Casein plays a huge part in what makes Real Milk Paint such a durable and versatile medium, seeing contemporary use in arts and crafts products such as glue, paints and photography emulsions. Composing up to 80% of the protein in cow’s milk, casein gets separated from other milk components via an ultrafiltration process where casein molecules unfold and bind to one another forming long chains. These chains intertwine with each other to form a mesh-like structure that strengthens the milk’s gel matrix and makes casein possible to be used for a variety of purposes, including making cheese and protein supplements.
Recently, casein has seen new use as an edible biopolymer food packaging, and this use harkens back to one of its original uses called casein plastic. Introduced in the United States in 1919, casein plastic has a consistency similar to celluloid and was often used to mimic the look of natural materials.
The History of Casein Plastic
The first plastic, cellulose nitrate, was developed in the mid-19th century and popularly used in the manufacture of cuffs and collars. In 1897, however, enterprising German printer Adolph Spitteler and his associate W. Krische made the scientific discovery that casein could be hardened with formaldehyde solution and patented their milk plastic process in 1911. This early form of wet casein plastic dough had a dyeable formulation and had the durability to handle washing, ironing and even dry-cleaning solvents, making it exceptionally popular for use in buttons, knitting needles, fountain pens and hair combs and for making artificial horn that mimicked the look of ivory. Though mostly replaced by modern petroleum-based plastics in the 21st century, some manufacturing firms that produce high-quality goods still make casein plastic.
Uses for Casein-Based Products
Currently, a USDA research team from the American Chemical Society in Philadelphia is researching milk protein-based food packaging. This milk protein, called casein, has excellent film-forming and coating properties that offer molecular flexibility that helps with emulsifying and stabilizing plastics formulations, and the team hopes to take advantage of these abilities to create food film. Though early attempts didn’t provide an effective moisture barrier, current iterations utilize a casein plastic reaction and chemical reaction with glycerol and citrus pectin to make biopolymers with structural soundness that protect food from oxygen, light and some humidity.
This innovation means we may end up seeing casein used to wrap single-serve products like string cheese and to make dissolvable packets for things like condiments, which has the potential to make modern life more sustainable by minimizing waste. And while scientists have pondered infusing these biopolymers with vitamins and nutrients to help boost the nutritional value of the foods they wrap, casein is used already in lots of food and technical products for a variety of other reasons we explore below.
Edible Casein Products
One of the most popular uses for casein in 2021 is in making protein powders, nutritional supplements and pharmaceutical tablets. This milk-based material is also extensively used to stabilize processed foods. For example, meat processors often use casein to improve texture and boost nutritional levels, while cheesemakers utilize the casein protein to bind fat and water while facilitating matrix formation. Known for its ability to thicken liquids, casein also adds texture and stabilizes ice cream as well as fat in whipped toppings.
Finally, casein’s ability to disperse rapidly when added to water makes it a main ingredient in dehydrated mixtures such as coffee creamers, processed cheese slices, powdered milk and instant cream-based soups.
Technical Casein Products
Technical casein products, or those used for something outside the food industry, have myriad uses. Since at least the Middle Ages, craftspeople have used wood glues and proto-cements derived from casein proteins, and glues created by combining the material with sodium hydroxide and calcium hydroxide have been in use from the mid-19th century to the current era. In fact, some industries prefer using water-soluble caseinates for labeling bottles, even though synthetic substitutes are available.
Since casein is one of the main ingredients in Real Milk Paint, you already know it’s a common paint additive. But you may not realize that in addition to use in milk paint, casein is also a component in water-soluble tempera paint thanks to its fast-drying properties. Andy Warhol even used this medium when he famously painted “Popeye” and “Dick Tracy” in 1960, and some artists continue to use this casein-based paint for current projects due to its superior ability to bind pigments — which also helps Real Milk Paint stay put on furniture, walls and artwork.
In the early 20th century, casein-based fibers and textiles were developed, though usage peaked around World War II when companies combined the medium with wood, cotton and rayon to create proprietary fibers like Aralac. These milk-based materials weren’t that strong, so manufacturing firms often wove them into other materials. For instance, since wool was scarce during wartime, casein-based fiber blends added to pure wool expanded the supply, though these utilitarian pieces were mostly plain-looking as the materials didn’t hold dye well.
In most instances, casein-based technical products like glue, paint and fiber were replaced by more cost-effective or durable synthetic materials. As society keeps searching for eco-friendly solutions to modern problems, however, we may yet see a return to using milk proteins for constructing everyday goods. For example, the Real Milk Paint Co. uses casein proteins in our Real Milk Paint colors, and a German company is currently making silky casein-based fabric.
Making Casein Plastic at Home
Whether you’re an artist, craftsman or dabbler, making a new milk-based material at home is a fun project to do alone or with kids. This DIY project renders a soft ball with the feel of processed cheese slices that you can mold and let dry in the shape you desire. To turn milk into plastic, you need the following supplies:
- Whole milk
- White vinegar
- Paper towels
- Fine mesh strainer
- 2-cup glass measuring cup
- Stirring spoon
First, stack five to six paper towels together, then pour a cup of milk into your glass measuring cup. Next, microwave the milk for 1 minute to heat it through without bringing it to a boil. Use a potholder to remove the measuring cup and add 4 teaspoons of white vinegar to the hot milk, stirring gently. You should see milk forms curds or casein clumps in your cup now, so use your stirring spoon to fish out as many as possible and place them on the paper towel stack. Once you finish this, use the fine mesh strainer to filter the remainder of the milk and white vinegar mixture.
Next, tap the strainer on the paper towels to add the solid casein clumps to your collection, then use more paper towels to gently pat them dry and soak up all the moisture you can. When the casein solids dry a bit, gather the dough-like paste balls that form together and knead them to create a smooth ball. Use this solid material just like clay, creating shapes by rolling it flat and stamping it with a cookie cutter. For a more artistic experience, you can also add food coloring to the solid mass for a completely customized casein plastic milk creation.
The Future of Casein Products
How much casein plastic will the future need? While casein-based plastics may never become as common as solid plastics or polymer-based plastic, these milk protein derivatives may aid modern humans more than expected. A need for more sustainable building materials continues to point to natural alternatives to polyester resins and oil-based polymers used in many plastic products, and modern innovations continue to make it easier to manufacture materials from natural components like casein. These developments may eventually make solid casein milk plastic a viable option for industries that require environmentally friendly solutions to contemporary problems.