By Published Aug. 30, 2023.
A few weeks ago, you wondered if you could toast bread in the microwave. Turns out you can’t, because microwave ovens don’t heat food the same way a toaster does.
But, you replied, what about Hot Pockets? Those get crisp and brown in the microwave.
Good point. The special “crisping sleeve” provided with a Hot Pocket and some other microwaveable snacks is the key.
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A microwave oven cooks food by bombarding it with energetic waves at a particular frequency. When the microwaves hit water molecules in the food, the molecules heat up, and the food cooks from within.
In order for food to get crisp, though, the exterior of the food needs to get hot enough to evaporate water. As the water is driven off, it leaves behind a crisply porous shell; because water is no longer keeping the temperature below 212 degrees, the surface also starts to undergo the delicious browning reactions that start at around 250 degrees.
That doesn’t happen in the microwave. As water evaporates from the surface, the surface absorbs less energy, not more, and the microwave energy starts to concentrate on the interior of the food. As a result, the interior can scorch while the surface just becomes dry, tough, and pale.
A crisping sleeve essentially behaves like a miniature standard oven inside a microwave oven. The sleeve is made of a thin layer of a specialized metallic material known as a susceptor. It is designed to absorb microwaves—much more than food does—and get very hot when it does.
Since the sleeve encloses the food, the heat from the sleeve cooks the surface of the food with radiant heat, just like a tiny toaster oven would; where the sleeve touches the food, heat is conducted directly, like cooking in a pan. In fact, the presence of the food is necessary to draw heat and prevent the sleeve from overheating and combusting.
Hot Pocket sleeves are single-use, because the conducting film inside them is fragmented during cooking and loses its susceptive ability.
In principle, yes, any food you wrap tightly in a microwave susceptor will get surface browning. In practice, the sleeves that come with Hot Pockets are engineered pretty specifically for the density, moisture content, and contours of Hot Pockets, and trying to wrap one around a frozen burrito will not give ideal results.
In the 1990s, there were several brands of generic susceptor sleeve on the market, such as Microcrisp and Brown & Crisp. The packaging of Brown & Crisp—vintage lots are still available on eBay—shows beautifully browned roast chicken and burgers, as well as Hot-Pocket-like turnovers. Evidently these products did not catch on, since they’re no longer made, and that’s probably because they didn’t work all that well. If I succumb to eBay curiosity, I’ll keep you posted.
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