Learn the science behind:
When & Why to Microwave Your Potatoes
Over 90% of what I use my microwave for (and with me, many others) is to reheat food. Only a small sliver of my microwave activity actually involves cooking food in it. And within that narrow realm of microwave cooking, there’s one food I cook in a microwave most often: the humble potato*.
Microwaving a potato has several great benefits. For one thing, the microwave slightly dries out a potato, making it easier to crisp it up later. The other: it cooks a potato incredibly fast. The reason it works so well? Microwaves just happen to be great at heating up water molecules, and a potato consists of a lot of water.
*Another great food to make in the microwave? Popcorn!
- Microwaves cook a potato fast
- But a microwave won't turn a potato crispy, nor brown
- Though makes it easier to crisp it up later
- Turn your potatoes to prevent hot spots
- Bigger potatoes take longer
- More potatoes take longer to cook
- Skin on or off?
- Keep the potatoes whole
- Cooking a whole potato – fast!
- Fast oven baked potatoes
- Just don't use a microwave when needing thin slices
Cooking a potato: softening and browning/crisping
When you prepare a potato, there are generally two things you’re after:
- The potato should be cooked throughout and as a result the inside should be tender and easy to chew. This transformation is mostly a result of the cooking and gelatinization of starch within the potato.
- Optionally, you might also be after a crunchy or crispy piece of potato. Maybe, you’d also like it to turn a slight light brown color, for extra flavor? Browning occurs because of the Maillard reaction, a chemical reaction that needs enough heat. Crisping up happens once the outside of a potato turns sufficiently dry.
To achieve one or both of these goals, there are plenty of ways to go about. You can deep fry them, boil them in water, fry them in a pan, bake them in the oven, or use an air fryer. So when would you choose to use a microwave to cook the potato? Mostly to speed things up. And, more often than not, you’d still use one of the other methods after it’s been microwaved.
Microwaves cook a potato fast
A microwave can cook a potato fast. Depending on the size and quantity of your potatoes, you can cook a whole potato within 6 minutes or so, from start to finish. Compare that to baking them in the oven, which can easily take an hour, or boiling them in hot water, often taking over 15 minutes. This is because microwaves do not heat up potatoes in the same way an oven or a stovetop does. Whereas ovens heat up air, and stoves heat up pots and pans, microwaves use waves – appropriately called microwaves – to heat potatoes. Whereas conventional methods heat potatoes from the outside-in, microwaves cook the whole potato in one go.
To do so, microwaves consist of waves of a specific length and frequency that are great at ‘exciting’ water molecules. That is, their frequency is such that they can get water molecules moving very easily. When molecules move more and more quickly, they heat up, the temperature increases. Potatoes contain a lot of water, over 80% of the weight of a raw potato is water. As such, a microwave is great at heating up a potato, but only up to about 100°C (212°F), the boiling point of water.
By heating up the water, the starch in the potato will start to cook. It will absorb water and gelatinize, softening the potato as a whole and making it digestible. This process requires temperatures well below the boiling point of water, so can take place in a microwave without any issues.
Microwaves fall on the so-called electromagnetic spectrum. Visible light, X-ray, UV-light, and radio waves are also made up of electromagnetic waves, but with different wavelengths. Humans can’t see microwaves, but we can see visible light.
But a microwave won’t turn a potato crispy, nor brown
That said, a microwave can’t create a crunchy, crispy potato, nor have it turn brown due. Both of these processes require temperatures above the boiling point of water. As a matter of fact, to turn a potato crispy you’ll need to evaporate significant amounts of water from the outside of a potato. The microwave is simply too humid and not hot enough, to do so. It’s why your potatoes will turn out cooked through perfectly, they won’t be brown, nor have a super crispy skin.
Though makes it easier to crisp it up later
Even though a microwave itself can’t create a crunchy potato, it can help you make a crunchy potato fast in a next step. This is because a potato pre-cooked in a microwave is relatively dry. You can cook potatoes in a microwave without adding any additional water. Just place them in the microwave and get going. This has a great advantage: potatoes don’t turn moister than they were to start with. If anything, they’ll dry out slightly. So compared to a potato pre-cooked in boiling water, or even steamed, it’s a lot drier. Compared to one cooked in the oven, it has a similar dryness, however, you got there a lot quicker.
Drying out the potato has a lot of advantages. During frying, 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. As such, it takes significantly less time to start crisping up and turning brown.
How to microwave potatoes
Microwaving potatoes is simple and doesn’t depend much on the type of potato you’re using:
- wash them;
- poke them – this helps steam escape through the skin and prevents little explosions of starch in your microwave;
- microwave them at max. wattage (eg. 900W).
If you feel comfortable trying it out, that’s all you need to know. But if you want some more guidance, or need some help troubleshooting, here’s a few things to watch out for.
Turn your potatoes to prevent hot spots
To ensure even cooking, make sure to turn your potatoes over about midway during cooking. Generally speaking, the bottom of your potato cooks faster than the top. This is because microwaves aren’t always great at evenly heating up food. Some parts of the food may be very hot, whereas others are still cool. This is because of how the waves travel through the food. They can strengthen but also weaken one another, causing these temperature differences. Microwaves with a rotating platter tend to have less of an issue with this problem, but if yours doesn’t have one of those, definitely make sure to move your potatoes around.
Bigger potatoes take longer
Size matters. Bigger potatoes do take longer to cook than small ones. That said, the difference isn’t as big as it is when cooking them in boiling water. If sizes don’t differ that much, you can easily cook them all together. Potatoes don’t easily overcook in the microwave, so some variation isn’t an issue. If you have some very small and some very large potatoes, it’s best to take the small ones out once they’re cooked and leave the large ones in to cook a little longer. As a starting point use the cooking times mentioned below:
- Small potatoes (2-5 cm / 1-2 inches) tend to take anywhere from 3-6 minutes to cook
- Medium-sized potatoes (5-8 cm / 2-3 inches) tend to take 5-8 minutes to cook
- Large potatoes will take >8 minutes to cook
More potatoes take longer to cook
The more potatoes you add to a microwave, the longer it takes for the potatoes to cook. This may feel contradictory if you’re used to cooking potatoes in boiling water. Once the water is boiling, it takes the same amount of time for the potatoes to cook, whether you’re cooking 1 or 20. That is not the case for a microwave, again, due to those waves. The power of your microwave is fixed with a certain wattage. If you add twice as many potatoes, let’s say 20, instead of 10, it still has a similar amount of energy available to cook those potatoes. As a result, it takes longer. It won’t take twice as long necessarily, but keep in mind that if you’re cooking potatoes for a party, it will take a lot longer than just cooking them for a few people.
Skin on or off?
You can cook a potato in the microwave with and without the skin. Which method you choose mostly depends on your personal preference. If it definitely easier to remove the skin of a raw potato, than it is to remove it from a cooked one. So, if you’re not a skin fan, taking it off in advance will be easier. However, removing the skin does impact the result of microwaving.
The skin protects potatoes during storage and helps keep moisture within – this is why it’s best to poke a few holes in whole skin-on potatoes, to allow some excess steam to escape. A peeled potato dries out more quickly than a potato that still has its skin on. In the microwave, the same applies. A potato cooked skin-on will remain moister. If you’re planning to fry or bake the potatoes afterwards, you won’t truly notice the difference, but if you’re using the potatoes in let’s say a salad, they can become a little chewy.
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.
Keep the potatoes whole
Cutting a potato has the same effect as peeling a potato, you’re removing the protective layer. But, it’s even a little worse since you’re also increasing the overall surface area. Potatoes cut into smaller pieces do run the risk of drying out in the microwave. As such, it’s often best to cook the potatoes whole and cut them once they get out of the microwave.
When to use the microwave for potatoes
Knowing all of the above, it’s clear that the microwave has a few key advantages for the following preparation scenarios.
Cooking a whole potato – fast!
Looking to cook a potato whether it’s for a salad or to eat as such, the microwave is your best friend. Potatoes cook fast and require barely any prep, especially if you decide to leave the skins on. It’s also a great step to take if you need cooked potatoes for another dish, such as samosas. Since it requires very little prep and tools, it’s a fast way to get started.
Fast oven baked potatoes
Baking wedges or pieces of potatoes in the oven can easily take an hour. You can cut down that time by half, if not more, if you pre-cook the potatoes in the microwave. Just cut them up and continue baking in the oven. Since the potatoes are cooked when you cut them, the cuts won’t be super smooth. This is actually a great advantage when you’re looking for crispy, crunchy potatoes. Those uneven bits and pieces crisp up a lot more easily.
Just don’t use a microwave when needing thin slices
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, a microwave is probably not your best bet. Making thin slices of your potato is just about impossible after you’ve pre-cooked the potato.
Marc Regier, Kai Knoerzer, Helmar Schubert, The Microwave Processing of Foods, Chapter 1&2, 2016, Woodhead Publishing, link