When researchers from the Okinawa Institute of Science and Technology and MIT got a bunch of taffy, they weren’t interested in the taste. They wanted to analyze the sweet and see just what gives the material its unique physical properties. As it turns out, the air bubbles and oil droplets are the primary factors determining the physical properties of taffy.

Taffy rheology

Saltwater taffy is a type of candy that has been a popular treat for over a century, especially in coastal areas of the United States. Despite its name, it doesn’t actually contain sea salt water. The “saltwater” in its name is more about marketing and the seaside resorts where it became famous, rather than its ingredients.

Taffy is typically made of table sugar, water, oil, and corn syrup. Butter and starch are also often added, as are flavorings and food coloring. To make taffy, you first need to boil the ingredients together until around 270°F (132°C). Then, the mixture is poured onto a cooling table and pulled. Traditionally, it’s pulled by hand, although taffy-making machines also exist.

This pulling process is what makes taffy ‘taffy’. It aerates the candy, giving it the distinctive texture and chewiness. Researchers would call this “rheology”.

“Taffy is a viscoelastic material — it has properties between a viscous liquid and an elastic solid,” said author San To Chan. “Comparing the deformation behavior of commercial taffy to those of different lab-made sugar syrups and lab-made taffies allowed us to identify the most important taffy ingredient (and material structure) that governs taffy rheology.”

Rheology is a branch of science that studies the flow of matter, primarily in liquid states, but also as soft solids or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force. A part of what makes rheology so interesting is that it explores how common substances like creams, shampoos, molten plastics, and even lava flow and deform.

So Chan and colleagues analyzed different components of taffy and how they influence the overall structure and flow. They found that the air bubbles and oil droplets are the primary factors determining the rheological properties of taffy.

“Taffy is composed of oil droplets and air bubbles of various sizes dispersed in a viscoelastic matrix (sugar syrup),” Chan said. “In some sense, oil droplets and air bubbles are like rubber balls. When deformed in the taffy, they tend to return to their original, spherical shape because of surface tension. In other words, emulsification and aeration make taffy more elastic, hence, chewier.”

Designing better sweets

From there on, researchers looked at how they could improve the properties of sweets. They found that emulsifiers, substances that help other substances mix better, can promote the formation of such small droplets, leading to a chewier, longer-lasting product.

Lecithin, in particular, was found to improve the desirable properties of taffy, and according to the researchers, this can also be used to tweak the taste of the taffy.

“Because of the larger amount of soy lecithin compared to commercial taffy, the lab-made taffy has a strong soy milk-like flavor, which I like,” said Chan.

The study comes as a reminder of the surprising amount of science inside a seemingly simple sweet.

The temperature to which the sugar mixture is heated, and the act of pulling the taffy, normally determines its final texture. Heating sugar creates different candy stages (like soft ball, hard ball, soft crack, hard crack) which result in different textures when cooled. The pulling process aerates the candy, which changes its texture from a hard, sugary lump to the soft and chewy delight we know and love. The chemistry of the mixture can also be tweaked to produce slightly different physical structures.

So, the next time you enjoy a piece of saltwater taffy, you’ll not only be savoring a sweet treat but also appreciating a bit of candy-making science.