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Authors: Jeffrey Steingarten
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with water, and fills up most of the cell. Separate, swollen, and perfectly intact potato cells make for smooth mashed potatoes. But at 160 degrees the cells are still strongly bound to one another, and if you try to mash the potato now, the cells will split rather than separate, and the starch gel will ooze out of them.
This is called free or extracellular starch, and it is the enemy. Free starch turns mashed potatoes gummy.
As the cooking time lengthens and the internal temperature of the potato increases to 180 degrees, the cement between the potato cells—pectic material similar to the pectin that thickens jams and .preserves—begins to degrade, and the cells can now separate from one another. This is a good time to mash your potatoes. With further cooking, the cells begin to weaken and rupture, and some of the gelled starch leaks out. That’s why overcooked potatoes become sticky and gluey even though they are easy to mash. If 15 or 20 percent of the cells in your potato are ruptured, you will be very sorry.
Buying your potato. One common way of categorizing potatoes is by their starch content. A mealy or floury potato like the Russet Burbank is dense, high in starch, low in water, and, despite the distasteful sound of the word “mealy,” generally preferred in this country for mashing. A waxy potato like the White Rose is low in starch, high in water, and often specified in French recipes. (Joel Robuchon’s potato is the BF 15; translated from the French this means a small yellow-skinned potato with dark yellow waxy flesh.) The adjectives “mealy” and “waxy” refer to the texture of the potato after you cook it. Mealy potatoes become fluffy and almost grainy when you mash them; waxy potatoes become creamy and smooth. But waxy potatoes generally require longer cooking and greater mashing force to separate the cells. Some researchers feel that more free starch is thus released, increasing the risk of gumminess.
Once you have decided which type of potato to cook, just try to ask your greengrocer or the guy stamping prices on laundry soap at your supermarket to point out the waxy potatoes and the mealy ones. Your reward will be an uncomprehending stare. But you can test the potatoes yourself. Buy one of each and, when you get home, mix a bowl of brine with nine and a half cups of water and one cup of salt. If a potato sinks into the brine, it is high in starch and will cook up mealy. If it floats, it belongs in the waxy category—unless it suffers from a potato ailment called hollow heart, in which case it will probably float in anything. All the potatoes at my grocery sank.
I used only large mealy Idaho russets in my mashed potato experiments. Avoid recipes that fail to specify which type of potato to use. Also avoid recipes that call for something like “six medium potatoes” without giving their total weight. Potatoes vary in size even more than human beings. If the cookbook specifies neither potato type nor total weight, discard it immediately.
Peeling and cutting your potato. The potato-peel lobby would have you believe that all the nutrients are in the skin. Nothing could be farther from the truth. The peel does contain a disproportionate share of vitamins and minerals compared to its negligible weight, but most of the nutrients are nonetheless found in the flesh of the potato and not in the peel. Cooking a whole potato in its peel does prevent some vitamins and flavor from leaching out into the salted water, but cooking any potato whole, whether you peel it or not, leads to uneven cooking when the rounded ends and outside layers become overcooked before the inside is ready. Overcooked cells will rupture.
If you peel your potatoes and cut them into pieces of the same size, they will cook evenly and quickly. Tiny pieces cook fastest but lose more nutrients and flavor because their total exposed surface area is larger. The best compromise is to cut peeled potatoes into slices between five-eighths
This is called free or extracellular starch, and it is the enemy. Free starch turns mashed potatoes gummy.
As the cooking time lengthens and the internal temperature of the potato increases to 180 degrees, the cement between the potato cells—pectic material similar to the pectin that thickens jams and .preserves—begins to degrade, and the cells can now separate from one another. This is a good time to mash your potatoes. With further cooking, the cells begin to weaken and rupture, and some of the gelled starch leaks out. That’s why overcooked potatoes become sticky and gluey even though they are easy to mash. If 15 or 20 percent of the cells in your potato are ruptured, you will be very sorry.
Buying your potato. One common way of categorizing potatoes is by their starch content. A mealy or floury potato like the Russet Burbank is dense, high in starch, low in water, and, despite the distasteful sound of the word “mealy,” generally preferred in this country for mashing. A waxy potato like the White Rose is low in starch, high in water, and often specified in French recipes. (Joel Robuchon’s potato is the BF 15; translated from the French this means a small yellow-skinned potato with dark yellow waxy flesh.) The adjectives “mealy” and “waxy” refer to the texture of the potato after you cook it. Mealy potatoes become fluffy and almost grainy when you mash them; waxy potatoes become creamy and smooth. But waxy potatoes generally require longer cooking and greater mashing force to separate the cells. Some researchers feel that more free starch is thus released, increasing the risk of gumminess.
Once you have decided which type of potato to cook, just try to ask your greengrocer or the guy stamping prices on laundry soap at your supermarket to point out the waxy potatoes and the mealy ones. Your reward will be an uncomprehending stare. But you can test the potatoes yourself. Buy one of each and, when you get home, mix a bowl of brine with nine and a half cups of water and one cup of salt. If a potato sinks into the brine, it is high in starch and will cook up mealy. If it floats, it belongs in the waxy category—unless it suffers from a potato ailment called hollow heart, in which case it will probably float in anything. All the potatoes at my grocery sank.
I used only large mealy Idaho russets in my mashed potato experiments. Avoid recipes that fail to specify which type of potato to use. Also avoid recipes that call for something like “six medium potatoes” without giving their total weight. Potatoes vary in size even more than human beings. If the cookbook specifies neither potato type nor total weight, discard it immediately.
Peeling and cutting your potato. The potato-peel lobby would have you believe that all the nutrients are in the skin. Nothing could be farther from the truth. The peel does contain a disproportionate share of vitamins and minerals compared to its negligible weight, but most of the nutrients are nonetheless found in the flesh of the potato and not in the peel. Cooking a whole potato in its peel does prevent some vitamins and flavor from leaching out into the salted water, but cooking any potato whole, whether you peel it or not, leads to uneven cooking when the rounded ends and outside layers become overcooked before the inside is ready. Overcooked cells will rupture.
If you peel your potatoes and cut them into pieces of the same size, they will cook evenly and quickly. Tiny pieces cook fastest but lose more nutrients and flavor because their total exposed surface area is larger. The best compromise is to cut peeled potatoes into slices between five-eighths
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