bread with mozzarella cheese and tomato in a toaster oven
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When you buy a shiny new toaster oven, you’ll probably want to keep it clean and new-looking for as long as possible. A common way to do that is by lining the broiler pan and crumb tray with foil to catch any droppings. If you look in your toaster oven’s manual, though, you’ll see that most brands tell you not to do this. It’s no surprise that foil and microwaves don’t go together, but foil is used a lot in regular ovens. So why is it an issue in toaster ovens?

It’s Not a Question of Basic Technology

There’s no fundamental reason to prevent the use of aluminum foil in a conventional oven as there is with a microwave oven. Putting foil in a microwave interferes with the way it operates, because foil blocks the microwaves themselves from reflecting around the oven as they’re supposed to.

Even worse, unshielded metal – like a bare piece of aluminum – can cause an electrical arc to occur inside the microwave oven, possibly damaging it or setting it on fire. At the very least, it’ll scare the heck out of you; at worst, it could potentially start a house fire.

None of this applies to toaster ovens, though. Toasters use the same basic technology as any regular oven, and people use foil in those all the time. So why do the manuals for some toaster ovens tell you not to use foil?

Aluminum Foil In a Toaster Oven

A toaster oven looks like a much simpler piece of equipment than a microwave, and in most ways, it is. It’s a relatively straightforward box with a couple of heating elements inside and some basic controls to make it do what it needs to do. Older models used simple mechanical timers, and modern ones have digital controls with microprocessors, but the basic design is still pretty simple.

That said, there’s a surprising amount of engineering that goes into a toaster oven, and most of it centers around how heat is managed. A toaster oven’s main job is to make good toast, and that means manipulating the heat so it’s evenly distributed around the cooking surface. You want your toast to be nicely browned from edge to edge with no dark or light patches, so that’s important.

Heat management also includes keeping the temperature inside the toaster oven within acceptable limits. Because they’re so compact and the heating elements are so close to everything else, the temperature in a toaster oven rises quickly. That’s a good thing up to a point, because it means your toast will happen faster. The downside is that if the temperature gets too high, your toaster oven can fail spectacularly.

Appliance designers and engineers manage heat largely by how air flows through the toaster oven. Foil can interfere with that airflow, and it’s one of the reasons why it’s dangerous in your oven if it’s not used properly.

Airflow Is Important in Your Oven

Let’s say, for example, that you’re going to broil yourself a pork chop. Heating up your regular oven for a single serving would be pretty wasteful, so you decide to broil it in your toaster oven. Rather than soaking and scrubbing the broiler tray afterwards, you may opt to line the tray with foil to catch the grease and drippings. It’s something people often do in a regular oven or in a toaster oven.

In the confined space of a toaster oven, though, it poses a problem. The foil that overlaps around the edges of your broiler pan interferes with airflow inside the oven, and it can cause excessive heat to build up at various points around the oven. This can cause the toaster oven to fail, or the edges of the foil itself could ignite.

Using foil to line the crumb tray at the bottom of your toaster oven can create similar issues. Air is meant to flow in around the crumb tray, and lining it with foil may block or sharply reduce that airflow. The buildup of heat you get as a result might kill your toaster oven.

Aluminum Conducts and Reflects

Lining the bottom of your toaster oven with foil can have another unfortunate effect. Foil reflects heat pretty capably, and the bottom of your toaster is usually quite close to the heating elements. The heat bouncing back from a foil-lined crumb tray can raise a heating element to a point higher than its design temperature, especially if airflow is also restricted. The end result is a heating element that fails, which is why so many manufacturers warn against this in their user manuals.

Aluminum reflects the indirect heat passing through the air from a heating element, but it’s also an excellent conductor of heat when it’s in direct contact with a heat source. That’s why it’s used so much in cookware. If you’re careless with your foil and it makes contact with the walls of your oven itself, it can conduct heat from point to point with unfortunate effects. The foil itself can melt – not something you want getting into your food – and it can create scorched or damaged spots inside your oven.

Aluminum is also a fine conductor of electricity, so if it comes into contact with the heating elements in your oven, it can arc or carry a current to places it shouldn’t go.

Best Intentions Meet Daily Use

One further argument for not using foil to line your crumb tray is simply human nature. It’s great that the foil catches crumbs and drips that might otherwise leak through the bottom of your toaster oven and get onto your counter. The flip side to that convenience is that those crumbs and dribbles of fat and juices build up on the foil. A mess on your counter is right out in the open and keeps you motivated to clean it up. A mess that’s hidden neatly inside the toaster oven doesn’t, and that’s a problem.

Most of the nasty stuff that builds up on the foil is flammable, and if you aren’t replacing the foil regularly, it can quickly build up to dangerous levels. Even if you’re normally something of a “neat freak,” it’s easy to overlook something you might only use in the bleary first-thing-in-the-morning hours. If you forget about the crumb tray or procrastinate a bit too long, that buildup can ignite and take out your toaster oven or possibly your kitchen.

The Answer Is Still Yes (Usually)

Despite all of those cautions and dire warnings, it certainly is possible to use aluminum foil in a toaster oven and use it safely. The general rule is to use it in ways that don’t block airflow within the toaster oven and that don’t create an opportunity for the foil to make contact with the sides, back or heating elements of your toaster oven.

Warranty is another factor to bear in mind, because manufacturers often advise against the foil and may consider your warranty void if you’ve used it. Oster’s toaster oven FAQ bluntly says not to use foil at all. Cuisinart’s manuals describe it as “not recommended” and explicitly warn against using it on the crumb tray or letting it touch the sides or elements of the toaster oven. Hamilton Beach and KitchenAid offer similar cautions.

If your toaster oven is out of warranty or if it’s inexpensive enough that replacing it on your own dime isn’t an issue, there’s no reason not to use foil. You just have to do it right.

Some Specific Uses for Foil

In some cases, you might still use foil to line a pan. Cuisinart grudgingly allows for the possibility, as long as you’ve wrapped the foil tightly at the pan’s edges, so it can’t come into contact with the oven’s walls. You can also trim a piece of foil to fit neatly at the bottom of a broiler pan, rather than going up and over the sides. You’ll have a bit more cleanup than you would if the pan was fully sheathed with foil, but it’ll keep food from burning and sticking directly to the pan.

A lot of toaster oven recipes suggest covering a pan for part of the cooking time to keep the food from getting too dark on top. Again, as long as you’ve wrapped it tightly and don’t let it contact the walls of the oven or the upper elements, this is fine. Roasts, cakes, loaves, casseroles and other foods may get darker in a toaster oven just because the upper element is so much closer. Loosely covering the top with foil can keep that from happening.

If your oven has convection, you’ll usually want to turn that off if you’re using loose foil. Otherwise, it can blow around the oven and get into places it shouldn’t.

If you prefer your potatoes in foil, there’s no reason not to do a baked potato in a toaster oven. On the rack or on a pan, they’re fine as long as the foil doesn’t touch the oven’s walls or elements. For crisp, unwrapped potatoes, oil them and salt them lightly and place them on a pan lined with a piece of cut-to-size foil. They’ll bake just as they would in a regular oven, but with an even crisper skin because they’re closer to the element.

You can even use foil to cook delicate fish or shellfish “en papillote,” which means in a pouch. Ordinarily, you’d use parchment, but parchment can ignite if it puffs up and gets too close to the element. With foil, spray it first with oil to keep the food from sticking; then fold and crimp the edges to make an airtight seal. Place the pouches on the toaster oven’s broiler tray and cook them according to your recipe.

Using Foil Bakeware

Aside from the roll you keep in your drawer, there’s another kind of foil to use in your toaster oven. There are several kinds of toaster oven-safe bakeware, including the usual metal, glass and porcelain options, but disposable foil bakeware is one of the most useful.

Normal casseroles can be converted to toaster oven recipes for one or two, for example, by just dividing the full batch into smaller takeout-style foil containers. They’re also a great tool for foods that don’t reheat well in the microwave, like fried chicken. Start them in a covered pan to keep moisture in as they reheat; then remove the cover and let them crisp up quickly once they’re warm.

Foil pans are also ideal for small-batch baking in the toaster oven. You can use conventional pans, but often a pan that should fit won’t because it’s got a built-in lip or handle that makes it just a bit too big for your oven. With foil, that’s not an issue. If the lip of a pan touches the sides of your oven, you can simply fold it up or crimp it down to make it fit. You can even gently squeeze the sides of the pan together to make it just a bit smaller or spread them out to make it lower and wider, as needed. You can’t do that with glass, and it makes foil one of the most useful forms of toaster oven bakeware.