Engineer Shows What Happens When Steam Pressure Forces an Apple to Peel Itself

Engineer Shane Wighton set out to answer a simple question that industrial food processors have quietly solved for decades. What if you could force a potato or apple to shed its own skin without a blade ever touching it? His answer involved building a high-pressure steam system dangerous enough that he ran every test from behind a blast chamber, operating valves remotely so he would not be standing next to something holding the energy of several sticks of dynamite.

Steam peelers have long been utilized in industrial potato chip production. A sealed vessel is filled with produce, and the chamber is saturated with high-pressure steam. The epidermis absorbs heat substantially faster than the underlying flesh. The water right beneath the epidermis gets fairly heated. When a fast valve is opened, the pressure lowers dramatically. The skin just peels away as the trapped water rapidly vaporizes and expands aggressively. Wighton had never seen such clear, fast-moving film of the incident before. He reasoned that it was time to create one that was transparent so that everyone could see the problem for themselves.

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He started by building a boiler out of thick-walled stainless steel tubes and plates. He machined the ends flat to provide a firm seal and installed high-temperature silicone gaskets between the faces. He held the whole thing together with some long threaded rods, but he knew stainless steel expanded far more than the rods when heated. Standard washers would have allowed the joint to slacken. Wighton piled some Belleville washers, which are conical spring disks that may be arranged to provide a continuous clamping force even as the metal increases. He had a 2 kW immersion heater submerged in the water, a mechanical safety valve to keep the pressure at 200 psi, and an air cylinder to safely open the outlet valve from a distance.

The produce was stored in a second chamber, which was similar to the first but included a quick-release valve and a viewing window. The window itself required meticulous design. A portion of an aluminum disk with o-rings squeezed a glass disk against the chamber. Since water under pressure retains far less energy than steam or compressed air, steam pressure plays an important role in seal retention. Leaks emerged, but the welds were repaired and the seats were cleaned. Only after that did steam enter the system.

Potatoes went first, and at 20 pressure, the skin barely moved, but at 40 psi, it began to crack open. Higher pressures provided full performance. In slow motion, the skin lifts, stretches, and peels away in large sheets that slap against the glass. Flesh loss remains minor. In one test, almost no real potato remained on to the discarded skin, indicating near-perfect separation, which is what commercial systems strive for on a daily basis.

Apples were followed by steam, which charged the valve and opened. The skin broke cleanly from the meat, and the apple itself deformed into something that appeared to have been hit by some fairly mean magic. The chamber was filled with the aroma of warm apples. Tomatoes shed their skins without any drama. Lemons developed several unusual surface blisters, necessitating even higher pressure or faster venting to complete the operation. Grapes have gotten mealy. Blackberries emptied themselves out, leaving hollow skins. Strawberries, on the other hand, performed something even odd, fragmenting into a mix of flesh and seeds that Wighton still cannot entirely comprehend. The high-speed footage simply prompted additional doubts.