Boiled Potatoes - How long?

Potatoes need to be boiled for about 25 minutes to be cooked, but this can vary from 15 minutes to 40 minutes, depending on four factors:

• Potato Size - Large potatoes take longer to cook than small potatoes. If you cut the potatoes into pieces an inch large, it takes about 25 minutes once the water is poiling. Medium-sized potatoes which are not cut take about 30 minutes and large uncut potatoes can take 40 minutes. If you cut the potatoes into very small pieces (for example, about a centimeter in size, to be used in a soup) then they can cook in as little as 15 minutes.
• New or Old - New potatoes (harvested in early summer, before they have a chance to develop a thick skin) cook faster than ordinary potatoes, by about 5 minutes.
• Mashed or not - If the potatoes are being served unmashed, then they can be a little firm. However, mashed potatoes should be soft and creamy. So, if you are going to mash the potatoes, boil them 5 minutes longer then otherwise to be sure.
• Variety - Some varieties of potato are firmer and can be cooked longer. However, in practice this is a small difference and can be ignored.

Since the cooking time depends on potato size, one should use potatoes of approximately the same size, or cut the potatoes to the same size. Otherwise, you will find that the large potatoes are still raw in the centre when the small potatoes are already over-cooked.

Likewise, it is simplist not to cook new and old potatoes together, as the new potatoes will tend to be cooked before the old ones.

There are two ways to test if a potato is cooked. One is simply to stick a small knife through it. If the knife goes through easily then the potato is cooked, if there is more than a little resistance, it is not cooked yet. If you are still not sure, remove a potato from the pot, place it on a place and cut it in half, they eat a piece from the centre of the cut potato to see if it is ready or not. If your potatoes vary in size, pick a larger potato (or piece of potato) for this test, as it is better to have the smaller potatoes slightly over-cooked than to have the larger potatoes under-cooked.

Peeling

New potatoes (see above) can be cooked with the skin on, as the skin is very thin. One needs only remove the loose bits before boiling by rubbing the potato in your hands while holding it under cold water. If you have very soft hands, you can use the rough side of a dish-washing sponge instead.

Older potatoes should have the skin peeled off, as most people dislike the taste and texture. As the skin has useful nutrients, peeling the potato after it is cooked increases the nutritional value. However, most people prefer to peel the potato before cooking because a cold potato is easier to handle than a hot one, and also it is usually more convienent to peel the potato in advance rather than when the meal is about to be served.

If you peel the potatoes before cooking, you can do this either with a knife or with a 'potato peeler'. The following photo is courtesy of Wikipedia, which provides a user guide in their potato peeler article.

If you peel your potatoes after cooking, the easiest way is the hold the potato in the air on a potato fork in your left hand and peel it with a knife in your right hand (reverse the above if you are left-handed). A potato fork is simply 3 prongs with a handle; following is a deluxe version:

Washing

The dirt should be washed off the potatoes before cooking. You can wash them before or after peeling. In both cases you can either wash them individually, or all together (in a sink, strainer or pot).

Green Potatoes

A green potato, or a potato with green spots, is generally a potato which has been exposed to sunlight (either before or after being harvested) and has produced chlorophyll (the chemical which is present in leaves, giving them their green colour). Although chlorophyll is safe, the potato also produces a poison known as 'solanine' in any part of the plant where chloropyhyll is produced. This is why the leaves and stems of the potato plant are poisonous.

Although a healthy adult would have to eat a large quantity of green potatoes to be in serious danger, a small amount can make one feel unwell (vomiting, diarrha, headaches). So, the best option is simply to discard any potato with a green tinge.

This article is provide as part of our How to Cook series, written to provide basic cooking skills.