How Play-Doh Works

Anyone who's ever played with the stuff knows that it's not just for modeling. Sure, you can shape it into a dog, a flower, a fish or a tree, and if you leave it to dry, your creation will harden into a sturdy, solid piece. But you can also mash it, squash it, pull it, roll it and cut it just for fun.

The most popular use for the dough, besides eating, is extruding. Many Play-Doh toys let you press the dough through a mold to create long ropes and other shapes. The first of these toys -- the Fun Factory -- hit the market in 1960, and versions of it are still available today. In other Play-Doh toys, extruded dough turns into a range of long, noodly objects, like a dog's tongue, soft-serve ice cream and hair that can be cut and styled.

Play-Doh compound can do all of this because of the interactions between its ingredients. The exact ingredients are a closely guarded secret, but Hasbro, the company that makes and distributes the compound, does reveal a few facts about its basic composition. The dough contains water, salt and flour. It doesn't contain peanuts, peanut oil or milk, but does contain wheat.

­According­ to the current Play-Doh patent (U.S. Patent 6,713,624), the compound is essentially a starch-based binder mixed with water, salt, lubricant and preservative. To be more specific, it contains:

Each of these ingredients has an effect on the compound's texture, fragrance and appearance. One of the major contributors to the softness and texture of Play-Doh compound is the interaction between its two primary ingredients - starch-based binder and water. To understand how the dough works, you have to know a little about starch and what happens when it comes into contact with water.

We'll look at the chemistry behind starch in the next section.

Starches are polysaccharides, or strings of sugar molecules. Starch consists of two types of molecules:

In a starch granule, amylose and amylopectin strands arrange themselves in a starburst around a central point called a hilum. Hydrogen bonds between the strands give the granule its shape. Granules come in a range of sizes, and different starches have different proportions of amylose and amylopectin.

If you add cold water to a starch, the granules absorb a little bit of it, but they remain pretty much unchanged. But if you add right amount of warm water, the starch granules swell, break down and release some of their contents into the water. In other words, they gelatinize. You can get a similar affect by mixing starch with cool water and heating it to its gelatinization temperature. Or, you can stir the mixture vigorously -- the mechanical action of stirring will help break the granules down. Check out the animation below to see just how this happens.

Lots of factors can affect the consistency of this gelatinous mix:

So that's the first clue to the chemistry of Play-Doh compound. The compound needs to be firm, but pliable. The starch it uses needs to have enough amylose to create sturdy, moldable dough. For these reasons, Play-Doh compound contains wheat starch, which contains around 25 percent amylose and 75 percent amylopectin.

We'll look at how other ingredients affect how Play-Doh compound works in the next section.

Amylose helps make Play-Doh compound sturdy and cohesive, but it has one drawback. As a starch-and-water mixture cools, the strands of amylose left in the water bind to each other. This is known as retrogradation, or set back. Retrogradation can cause dough to harden permanently.

For this reason, Play-Doh compound includes a retrogradation inhibitor -- a substance that keeps the amylose strands from sticking together. Play-Doh includes amylopectin or a waxy starch to act as a retrogradation inhibitor.

Extra amylopectin, though, can cause Play-Doh compound to become a sticky paste rather than a smooth gel. For this reason, Play-Doh includes ingredients to improve its texture and consistency -- a lubricant, like mineral oil or vegetable oil, and a surfactant.

You can find surfactants -- also called surface active agents -- in cleaning products in your home. Surfactants are artificially manufactured molecules whose jobs are to suspend substances in water. They can do this because of their unique molecular structure. One end of the surfactant molecule is hydrophilic -- it likes water. The other end is lipophilic -- it likes fats. The lipophilic end is also referred to as being hydrophobic.

If you add a solution of surfactant and water to a fat, the lipophilic ends of the surfactant molecules will bind to fat molecules. The hydrophilic end of the molecules will bind to nearby water molecules. In this way, the fat becomes suspended in the water. (With different proportions, water could also become suspended in a fat). In Play-Doh compound, surfactants bind to molecules of lubricant and suspend them in the starch-and-water solution. This reduces the compound's stickiness.

So, with this combination of ingredients -- starch, water, retrogradation inhibitor, surfactant and lubricant -- you get a pliable compound that's smooth instead of sticky. The rest of the Play-Doh ingredients fine-tune the dough and give it its color and fragrance. Salt adds some antimicrobial properties and reduces the number of free water molecules. Hardeners and humectants can make the compound harder or moister if needed. Preservative increases the shelf life, and fragrance and color add the final finishing touches. Manufacturing Play-Doh compound essentially requires mixing all of these ingredients together and placing the mixture into sealable containers.

We'll learn about several recipes for making homemade Play-Doh in the next section.

Some people would prefer not to buy Play-Doh compound at the store. They'd rather save a little money and give children a modeling compound that's actually edible. (Play-Doh compound is nontoxic, but it does include some ingredients that aren't really meant for eating. For example, the lubricant is most likely petroleum based.) For these reasons, recipes for homemade dough usually use common food ingredients that have similar qualities to what you find in Play-Doh compound.

In the interest of science, we made several of these recipes. We wanted to explore how their ingredients and consistency compare to that of store-bought Play-Doh compound. We also wanted to judge the all-important factor of flavor -- after all, just because Play-Doh compound isn't made for eating doesn't mean that people don't eat it. Here's what we found.

Cooked Flour Dough

(We found this recipe at Kids' Turn Central.)

The first recipe we tried used flour, cold water, salt, vegetable oil, and cream of tartar. Like Play-Doh compound, this dough is a mix of starch, water, salt and a lubricant, and it uses heat to help the starch gelatinize. But one of the most important ingredients in the recipe is cream of tartar, another term for acid potassium tartrate. Cream of tartar is a byproduct of wine fermentation, and it's used in cooking to stiffen liquids like egg whites. In this recipe, it makes the dough stronger and stiffer.

The cooking step is a little challenging -- you need to stir the mixture constantly. After a while, it becomes a thick, hard-to-stir mass that may stick to some cookware.

This recipe produces dough that's pretty fun to play with. It's a little stickier to the touch than store-bought Play-Doh compound, but it has about the same softness and can be kneaded easily. The dough also holds its shape very well, thanks to the cream of tartar's stiffening ability. Although all of its ingredients are edible, it does contain a lot of salt.

In the next section, we'll take a look at an edible Play-Doh recipe.

(We found this recipe at Lisa's Kids Page.)

Our second test recipe uses peanut butter, light corn syrup, powdered milk and powdered sugar. After reviewing the sugar-heavy list of ingredients, we suspected that the result would be a sticky mess.

However, the peanut oil found in peanut butter adds a substantial amount of lubrication. The recipe's moist ingredients -- the peanut butter and the corn syrup -- are also fairly thick. The result is a cohesive ball of peanut butter dough that quickly sets up enough to bog down a mixer.

Surprisingly, the peanut butter dough isn't sticky -- it's oily. Even though it appears dry at first, it becomes oily to the touch within a few seconds of kneading. It also requires refrigeration, and the resulting dough is like a stiff, cold log. It's also brown, so you can't really add color.

On the other hand, it's edible, except by people with peanut allergies or diabetes, and unlike the other recipes, it tastes very good. In fact, the main benefit of this recipe is its flavor. Its oiliness doesn't encourage lots of play, but its taste encourages lots of eating. It's more like a dessert than a modeling compound.

A similar recipe uses honey instead of light corn syrup.

(We found this recipe at Kids' Central.)

The no-cook dough recipe we tried has many of the same ingredients as our first experiment did -- water, salt, vegetable oil and flour. It also includes a little cornstarch as a thickener. The big difference is that it uses cold water and does not require cooking.

Getting the right balance between flour and water was a little tricky with this recipe, and getting a smooth ball took lots of mixing -- a side effect of working without heat. In the end, we had a dough ball that strongly resembled the dough we made on the stove.

At first, the no-cook dough was a little stickier and less cohesive than the cooked dough. The cooked dough recipe made a soft but firm, workable dough that held its shape well, even when we stored it in a plastic bag. As we played with it, it just got stickier. At first, we blamed the Georgia summer humidity. But when we put the uncooked dough in an airtight plastic bag, it gradually spread into goopy mush. Adding cream of tartar to the recipe might stiffen the dough enough to make it more workable.

Here's a chart of our homemade dough findings.

Check out the links on the next page for lots more information about Play-Doh modeling compound and related topics.