A Popsicle

History has it that the Popsicle was invented (or discovered) by an 11-year old California boy who accidentally left his soda, with a stirring stick still in it, outside on a cold night. The next morning he had frozen soda on a stick. He called it an Epsicle, a play on icicle and his name, Frank Epperson. It took him nearly 20 years to obtain a patent for the Epsicle ice pop, which was later renamed “Popsicle“by the encouragement of his kids.

Popsicle has come a long way since the days of Frank Epperson. Instead of soda, the ingredient list contains sugars, stabilizers, colors, and flavors. Color and flavor are important for consumer appeal, but it’s the choice of sugars and stabilizers that governs the physical attributes of the Popsicle. Without sugars and stabilizers, it would just be a colored ice cube.

Sugars reduce the freezing point of water. That is, sugared water freezes at a lower temperature than pure water, which means that, even though it seems pretty hard, there is still some liquid water in a frozen Popsicle. A Popsicle is essentially a bunch of ice crystals held together by a slush that contains dissolved sugars, colors, and flavors. The more ice (less slush), the harder the Popsicle.

Frank Epperson

The manufacturing process is also much more high tech than what Frank Epperson did. Thousands of Popsicles are made every hour in modern continuous automated Popsicle freezers. The sugar concoction is deposited into molds and then submerged in a very cold brine (saltwater) to induce rapid freezing. Sticks are added just as the mixture freezes. This type of freezing, called quiescent freezing because there is no stirring, results in long, needle-like ice crystals. They form initially at the mold surface where it’s coldest and then grow radially inwards, toward the center of the mold. All ice crystals lead to the stick. Next time you bite into a Popsicle, check out the pattern of ice formation.

Popsicles have also developed beyond the single stick variety. There are numerous variations to the traditional one-stick Popsicle of Frank Epperson. There are twin pops, with two sticks and two Popsicles, joined at the hip. There’s the rocket pop, a multicolored ice pop made by sequentially freezing three or four different layers of sugar syrup. There are Popsicles that glow in the dark, with a glow stick inserted down the middle. You can even make your own frozen ice pop, just like we did as kids, by pouring liquid Jell-O, Kool-Aid or fruit juice into molds and letting them solidify in the freezer.

Next time you pull one out of your freezer, study the ice crystals while you enjoy the cool refreshment. A Popsicle may be a simple treat, but there is still a lot of science involved.