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You might think that one potato is pretty much the same as the next. But bake a russet potato and a red potato and the two will emerge from the oven completely different—one light and fluffy, the other creamy and dense. What it comes down to is this: All potatoes are not created equal.
The average supermarket has at least four or five different varieties of potato. But there are more than 200 different varieties in the world! Each are different from one to the next. But they do share some basic traits. We’ll start there.
All potatoes consist mainly of two things: starch and moisture. The density of each variety correlates to the amount of starch in the potato, which can range from 16 to 22 percent. (Remember: Starch is denser than water.) Knowing the amount of starch in whatever potato you plan to use for dinner is important. This is because the amount of starch will have a great effect on the potato’s final texture.
How can you tell?
Well, you could take our word for it. But here is a fun way to figure out the density of a particular potato right in your home kitchen.
To determine the difference in density of potato varieties, we mixed up an 11 percent salt solution and split it between three containers. We then added a Red Bliss, Yukon Gold, and russet potato, respectively.
The Red Bliss floated straight to the top. The russet sank like a rock. And the Yukon Gold was suspended right in the middle. Why?
Because russets have the highest proportion of starch, meaning that they are the densest, and therefore sunk. Red Bliss are the least starchy (and thus contain more water). Yukons are right in the middle.
The second important factor to consider is the ratio of the two starches, amylose and amylopectin. Russets not only contain more starch, but they also have a higher percentage of amylose, whose long chains separate when exposed to heat. This separation opens up room for moisture like butter and cream to be sucked into the potato, making them the perfect choice for mashed potatoes.
Left: Before cooking, the potato starch amylose is held within the starch granules. Right: When cooked (or, more often, overcooked) these starch granules swell with water and then burst, releasing the amylose, which forms a gluey gel.
Red Bliss contain a greater amount of amylopectin, whose branched structure holds together when exposed to heat. Less moisture is sucked into a red bliss as it cooks, and more of their original shape is preserved. These characteristics make red bliss a great choice for potato salad, or soup.
It’s easy to talk about this, but it’s harder to show it. We came up with a way to see the difference in starches by cooking cubes of each variety of potato in water dyed with blue food coloring.
The russets’ greater amount of starch, and higher ratio of amylose, means they suck up a lot of the blue color during cooking.
In contrast, the red bliss show only a fine line of blue around the edge.
Once again, Yukon Golds sit right in the middle.
And what does this all mean? Because each type of potato has a different ratio of starch to moisture and a different ratio of amylose to amylopectin, and each behaves in different ways when exposed to water and heat, it’s important to pay attention to what kind of potato you choose for different recipe.
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Our recipe for Potato Galette is free through October 15, 2012.
Got any potato questions? Leave ‘em in the comments.