I made a toaster waffle for myself this morning. Growing impatient, I popped it out before it was all the way done. As I was buttering it, I noticed parts of the waffle were still cold. Since there was already butter and syrup on it, I couldn’t put it back in the toaster. I threw it in the microwave for 20 seconds and it came out floppy instead of crispy. What gives?
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Your toaster doesn’t heat things with microwaves. It heats them with heat. Microwaves heat the thing itself by moving the water around in it really really really fast. The toaster is a hot thing itself which heats other things.
Microwave heating penetrates into food a little bit – certainly enough to get to the middle of a slice of bread. It heats all the bread evenly, and microwaves are really good at heating up water (no, this is not because they’re set to the resonant frequency of water – that is a myth). So all the water in the middle of your bread gets heated up, some of it turns to vapor, and your bread gets steamed. Steaming foods generally makes them soft and floppy. This also prevents the heat from reaching above 100 C – any more heat than that will just go into boiling that water – and 100 C is not enough to have crispification occur.
Toasters, on the other hand, use infrared radiation which cannot penetrate food that well. This heat hits just the surface of the bread, boils off the water on the surface, and goes on to get the surface much hotter than 100 C. This is hot enough to set off the famous Maillard reaction, which combines sugars and amino acids in the bread into those yummy brown polymers we love to eat.
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Toasters heat bread from the outside. The heat gets concentrated on the outer layer of bread. Water evaporates from this outer layer, which lets it get even hotter (the presence of water keeps stuff below water’s boiling point), to the point that it browns and crisps up. It also helps that the bread is placed vertically between grills (or laid horizontally on a grill, if it’s a toaster oven) that allow air to circulate around the bread, so water vapor can escape.
Microwaves (1) heat bread from the inside (sort of) and (2) they don’t (typically) allow air to circulate around the bread. Let’s start with number 1. Microwave ovens heat stuff by sending electromagnetic waves (microwaves, specifically) into the stuff. These waves make the atoms inside the stuff jiggle faster (faster-jiggling atoms are hotter – that is basically what heat, or at least temperature, is). Microwaves can penetrate some distance into food. How far depends on the food, and it’s not super far. You won’t heat up the inside of a frozen chicken before the outside has thawed. But they do go deep enough into a slice of bread to basically be heating the bread evenly.
As the bread is heated, water is evaporating from it, but because the slice of bread is resting on a plate (most likely), it can’t actually escape from the bottom. Instead, it condenses onto the plate below, and this liquid water gets reabsorbed into the bread. And even the top surface of the slice is staying moist, as water from the interior of the slice is getting forced out. So, no crisping can occur as the surface doesn’t get hot enough. Meanwhile, the (relatively) mild and moist heat is causing the starches in the bread to (re-)gelatinize. You know that moist, soft texture that freshly baked bread has? That’s because the fresh, warm bread still has gelatinized starch. As the bread cools, the starches harden a bit and so you get a drier, firmer texture. If you reheat bread, you will re-gelatinize the starches (somewhat) and return it to this softer, freshly baked-like texture, which for a slice of bread will make it rather floppy. Meanwhile, the water that condensed onto the plate may also get absorbed into the crust of the bread, which turns soggy when it gets wet.
If you keep heating the bread longer in the microwave, and especially if you allow for better air circulation (e.g. by standing the slice on its end some how), you will find that the bread does get crispy, and may even burn. Only, it (probably) won’t get the same nice consistency as a well toasted slice. Because the bread is heating all the way through, water evaporates everywhere too, and so the slice will dry out and harden as you are basically boiling the bread from the inside until most of the water is gone. Whereas, in a toaster, the interior of the slice will stay somewhat soft and moist (at least if you don’t take it too far) because the heat is applied from the outside.
Microwaves (the electromagnetic waves) are particularly well-absorbed by water molecules.
When you “microwave” something you’re basically heating up all the water molecules really-well and the other molecules only kinda-well; if you heat things up *enough* you’ll turn more and more of those water molecules into steam.
The reason why microwave-versus-toaster is giving you different results is because you are essentially cooking by steaming (hot wet) in the microwave oven and essentially cooking by baking (hot dry) in the toaster.
Because a microwave does not generate heat. It generates a specific kind of electromagnetic wave that is really good at exciting (i.e. making hot) water and fat molecules.
So, really what you are asking is “why is my steamed bread floppy, but my dried burnt bread crispy”. Which should be kinda self explanatory.
The thing you need to understand about a microwave, is that it is not filling the box with hot air. Ovens using whether gas or electric are heating the entire space within the oven. A microwave is using electromagnetic radiation to excite water molecules within the food. Because heating food is just a transfer of energy. Using radiation to excite molecules in the food, heats it up. You’ll notice that aside from the steam coming off your now heated food, the air inside the microwave isn’t even warm. That’s the power of microwave radiation.
Unfortunately, as others have said, because you’re heating the water molecules within the food and not directly heating the food, sometimes the water boils off and steams your food making it soggy. This is also why, some foods just aren’t the same when you re-heat them in the microwave.
This is also why you should add a cup with some water in it when heating up a heat pack. Without the cup of water, you run the risk of burning the grains in the heat pack.
Same reason going to Florida will frizz your hair while going to Arizona will dry out your skin, it’s the humidity.
Because it doesnt produce heat Like an oven or a toaster and roasts the bread with it. It makes the water inside the bread hot and stramy, which of course makes the bread floppy
It depends, the microwave heats stuff from the inside by heating up all water molecules. Give it just a little bit more time in the microwave and your floppy dish will turn into a hard brick because all the water evaporated
If you use a toaster, you’re heating from the outside, most stuff with a crust doesn’t transfer heat very well, so it’s easy to burn it at the outside while it’s still frozen on the inside. All in all, the water is also evaporating slower using a toaster which compared to the microwave doesn’t steam the outside and makes it floppy
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