We’ve Discovered a New Trick: The Science of Slice Reheating
While I enjoy cold pizza, I frequently wish for the glory days of fresh pizza. I remember when you could get away with stingy mozzarella if you could get your hands on a tasty, tangy tomato sauce with whatever toppings you wanted. Fresh pizza made precisely to your specifications. Once your order was in, a craftsperson created it and slid it gently into the hot oven. Grab the pizza box, head to the door, and get in the car.
It was always hard not to sneak a slice out of the hot pizza box while driving, as the smell was overwhelming. Allow that hot slice to cool before biting into it to avoid burning the roof of your mouth. Understanding that it’s hard to turn back the clock on a pizza, which begins to degrade after it comes out of the oven, I’d never considered whether there was an optimal way to reheat cold pizza. The best you could do was put it in a hot oven until it was heated and accept that the crust on a reheated slice would never approach the texture of a freshly baked one. When a piece is still fresh, the stove can bring back some of its crispness and flexibility, but it will lose most of its moisture. No matter how tasty, a reheated slice will always be crispier, drier, and more rigid than the original because some of the water in the authentic piece will have evaporated.
Nevertheless, I’ve now discovered a better approach for minimizing moisture loss. It is crucial to keep the moisture in the pizza when reheating, or the crust turns into a substance that is too hard to eat. I found it by chance when I chose not to waste time heating my entire oven to reheat a few little pieces. I didn’t have a toaster oven, which most people use to reheat pizza slices, so I tried cooking my articles on the grill on my stove, which I use sparingly. When not in use, they are beneath the stainless-steel lid.
The slices would roast significantly more quickly and efficiently than in the oven. The lid would form a shallow oven-like compartment, allowing them to be baked thoroughly rather than just from below. But I was so hungry then that I couldn’t wait for the grill to heat up. Instead, I just placed the slices on the chilly grill, covered them, and turned it on. I didn’t want to scorch or overcook the pieces because they’d be so close to the gas burner, so I set the skillet to its lowest setting (200 °F).
After about 30 minutes, a puff of steam and my completely transformed slices emerged under the lid. They were no longer the rigid, somewhat bent pieces they had been when cold; the cheese on them was gooey and glossy. While these slices were not nearly as excellent as they had been while fresh—they were slightly sharper and drier—they had a significant fresher feel than I had ever tasted in a reheated slice. The crust was soft on the inside yet crunchy on the outside, the cheese melted, and the toppings were supple and hot.
I experimented with the process a few times. I had leftover pizza to ensure I understood the technique. I knew the moisture- and the heat-trapping cover was critical, but I needed to find out how to heat it. I tried placing the slices on a preheated grill, which helped to over-crisp them and dry them off, leaving them as hard as boards. Therefore, I found that the three most important aspects of the procedure were starting from scratch, covering the grill, and heating the slices below the boiling point of water (212°F).
Retrogradation
To understand why this strategy worked so effectively, it’s first necessary to grasp what happens to the crust once a slice of pizza starts its inevitable post-bake slide. It doesn’t only stiffen because it’s cold; it ages like a loaf of bread.
Staling, or retrogradation, is how the bread starches release the water they hold and firm up. Let’s say you reheat the bread above 140°F, which is the point at which the wheat starches soak up water and turn gelatinous. In that case, you can stop some of the staleness from happening if the water released by the starches stays in the gluten and makes it soft and pliable, so toasting a slightly stale slice of bread can bring back its suppleness.
But, if the water produced by the starches escapes from the bread, either gradually or quickly, when heated over the boiling point (212°F), the starches will no longer have water to reabsorb, and all hope is gone.
Pizza in a hot oven acts like toast: the outside (including the cheese and toppings) gets hot, loses water, and gets hard immediately. Only the slice’s inside retains enough moisture to re-gelatinize. So, to make the best-reheated pizza slice, heat it above the gelatinization threshold but below the point where it steams. The cut is to the gelatinization point when heated gently on a covered grill. A trace of water dissipates in evaporation, primarily in the one spot you want it to happen: the bottom crust. Less water evaporates by rewarming the slice in a small, closed space. When I removed the skillet’s cover, a puff of steam came out, which helped soften the cheese and toppings. Fortunately, no. The process works just as well in a covered skillet, especially one with a lid that fits tightly and is as shallow as possible to keep as little water as possible from escaping as steam. The only problem with the skillet method is that you can only heat two or three slices simultaneously.
Retrogradation happens most quickly at temperatures just above freezing. Instead of putting leftover pizza in the fridge, leave it on the table and eat it before it goes bad.