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Microwaves are often a little under-valued, forgotten about pieces of kitchen equipment. Even though a lot of people own a microwave, most of us (including ourselves…) mostly use a microwave to (re)heat food. A microwave is very good at heating food, that’s definitely true, but it can do more and in some cases, can actually be a preferred way of cooking your food!
Cooking potatoes is a great example of getting the most out of your microwave. Microwaving a potato actually has a few great benefits, that can help great better (and easier) potato dishes. Our favorite: combining a microwave + air fryer/pan frying to make deliciously crispy potatoes.
Microwaving a potato isn’t hard and we could explain that in a minute or two. But of course, we want to know what happens when you cook that potato. Why is a microwave so good at it? And, as such, how else could you use a microwave to prepare your food?
How does a microwave work?
How you ever considered how you’d always use gloves or towels when putting your hand in a hot oven, but that there’s no need to do that when putting your hand in a microwave? You might need a gloves or towel to take out your food after it’s been heated in the microwave. But your hand doesn’t get hot from just being in an open microwave that has just worked!
This is because microwaves don’t heat up your food in the same way as say an oven or a stove do. A gas stove burns gas to create heat. An electric oven uses electricity to heat up coils, that become hot to the touch. A product heats up from the outside going in through conduction of the heat. Especially for large food products, it can take a long time for the heat to travel all the way through.
Microwaves on the other hand don’t create this direct heat. Instead, they use radiation to warm up food. This radiation is made up of waves of a specific length and frequency (0,3 – 300 GHz, but most consumer market microwaves work at 2,45 GHz). Humans can’t see microwaves, they’re not the correct length to be registered by our eyes.
Microwaves fall on the so-called electromagnetic spectrum. This is made up of ways of very short to very long wavelengths. Visible light, X-ray, UV-light, but also radio waves are all similar electromagnetic waves, but with different wavelengths.
Exciting water molecules
In a microwave, these ways move through your food. The waves themselves aren’t warm. However, this specific type of wave is very good at ‘exciting’ various types of molecules in your food, water especially. If microwaves travel through water, the water molecules will start to vibrate considerably. This causes the temperature to increase (the kinetic energy increases). Microwaves are especially good at heating up liquids and so will have more trouble with solid (frozen) ice.
Potatoes contain a lot of water (over 80% of the weight of a raw potato is water). This makes microwaves suitable for heating up potatoes.
You may have noticed that microwaves aren’t always great at evenly heating up food. Instead, microwaved food might contain hot spots where the food is very hot. Other areas might not yet be as warm. This is because of how the waves travel through the food. They can strengthen but also weaken one another. It is why some microwaves contain a rotating platter, to have the food move through these different areas. In other cases, you might be advised to mix your food midway to even out the heat.
For potatoes specifically our experience is that the bottom of the potatoes cooks faster than the top. As such, you might need to rotate them mid way.
A lot of the behavior of the waves in a microwave is very similar to that of waves in water, on a lake, or ocean. They ripple through, might interact, and cause different patterns.
Waves traveling through
When heating your potatoes the waves travel through your potatoes. When a wave hits your potato it does weaken the further it gets into the potato. Also, large potatoes need a lot more waves traveling through them before all the water molecules are fully excited. Large potatoes still take longer to cook than smaller ones, but still considerably faster than if you’d cook them in a pot of boiling water or a regular oven.
What Happens When You Microwave Potatoes
So the microwaves heat up the water molecules within the potato. This is what eventually ‘cooks’ the potato. The heat will cook (gelatinize) the starch in the potato, the cell walls between cells will soften and break down. Some cells within the potato might even break down, releasing their components. All these processes are very similar to what happens whenever you cook a potato. The chemistry and science remain the same.
Drying out the potato
Even though the processes are the same, a microwaved potato will come out slightly different than that same potato cooked in boiling water. For one thing, you can microwave potatoes without any additional water. All you need to do is place them in the microwave on a microwave-proof bowl. As such, the potatoes won’t be able to absorb any additional moisture (which they would do to some extent when boiled in water). What’s more, microwaves do dry out food a little. Because they heat up water so well, some of that water will evaporate.
Drying out a potato (or at least not adding any extra water), has a lot of advantages if you’re planning to continue cooking that potato! When you’re frying, whether that’s in a pan or deep-fryer, you spend a lot of energy evaporating moisture. The moisture needs to be evaporated to get a crispy outside. If your potato starts with less water, you need to evaporate less. Also, it runs less of a risk to stick to a pan.
Did you know that a well-developed ready-to-heat meal for a microwave has a different optimal composition than one for the oven or stovetop? Developers might use a little extra water or design the packaging shape in such a way that the waves can travel through optimally!
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A microwave can cook your potato to make it ready to eat. However, it can’t brown your potatoes or truly crisp them up. Browning only happens at higher temperatures, where the Maillard reaction can take place rapidly. Potatoes in the microwave just don’t get hot enough.
When to microwave your potatoes
Knowing all of the above, when would using a microwave to cook your potatoes be a good option?:
- To cook a whole potato; because the waves travel into the food more easily than heat would travel through conduction, your potato will cook quickly
- You could use it to make a whole baked potato
- To pre-cook potatoes for (deep) frying. The microwave quickly heats up the whole potato and dries it out slightly. This provides the ideal starting point for then frying and browning those potatoes.
- Microwave + air fryer is a great combination that we tested previously!
- To cook your potatoes. If you just want cooked potatoes, a microwave does the job very well. They might be a little drier compared to ones boiled in water, but if you prefer it that way, it’s a great fit!
Of course, the microwave isn’t a magic tool and it doesn’t always add value. If you’re planning on making a gratin for instance, with thinly sliced potatoes, we don’t recommend using the microwave. Making thin slices of your potato is just about impossible after you’ve pre-cooked the potato.
Skin on or off?
The skin of a potato protects it during storage. A peeled raw potato will dry out a lot more quickly than a potato that still has its skin on. The skin performs this same role in the microwave! By keeping on the skin more moisture will remain in the potato. In our experience, it’s almost always better to keep on the skin. Peeling the potato can result in potatoes that are truly too dry. Doesn’t mean it can’t be done, but for most applications it’s not desirable.
Of course, there are exceptions to just about every rule. If you’re looking for a way to cook and really dry out your potato peeling the potato can help a lot here. In that case, be sure to also let some of the steam and water escape from the microwave midway during cooking.
To cube or not to cube?
Since we’d recommend leaving the skin on, we also recommend not cutting your potato into smaller pieces. Once you cut them, you’re effectively peeling parts of the potato, making them vulnerable to drying out. Also, a microwave is actually pretty good at cooking large potatoes. As such, the need to cut them into smaller pieces (as you would when wanting to boil them quickly in a pot of boiling water) just isn’t really there.
If you’re planning to use your microwaved potatoes for making fries, we definitely recommend cutting them after cooking in the microwave! By pre-cooking the potatoes they turn soft and just a little crumbly. Your cuts won’t be as smooth anymore and you’ll have little bits and pieces on the sides. These pieces crisp up very easily during baking or frying. As such, it’s even easier to get crisper potatoes!
Marc Regier, Kai Knoerzer, Helmar Schubert, The Microwave Processing of Foods, Chapter 1&2, 2016, Woodhead Publishing, link