The Starchy Secrets to Cooking Potatoes

When cooked, the cells of starchier spuds such as russets soak up more cooking water and interstitial moisture, which causes their cells to swell and push each other apart, resulting in a dry, fluffy interior that eagerly soaks up flavorful liquids such as cream and butter. Meanwhile, low-starch varieties such as red potatoes absorb less moisture into their cells and thus contain more free moisture. That water gets absorbed by pectin that’s released from the cell walls during cooking and forms a gel that holds the cells together, creating a waxy potato’s famously dense, creamy consistency. The moderate starch content and absorption of Yukon Gold potatoes is what makes them so versatile; they cook up neither dry nor dense but velvety.   

Cooking cubes of each potato type in water dyed deep blue shows the difference in absorption. The dye travels deep into the russets, seeps a little into the Yukon Golds, and forms only a thin line around the exterior of the red potatoes.

When baking a russet potato, our goal is for its starch to soak up so much interstitial water that its cells swell and separate, rendering the interior uniformly dry and fluffy. We found that this happens when the spud’s core surpasses 205 degrees, so it’s important to check its doneness with a thermometer.

Rice, Don’t Mash: Unlike conventional potato mashers, which require repeated smashing that can burst the spuds’ cells and cause them to spill gluey starch, a ricer forces each cooked spud through a perforated disk only once. Thus, fewer cells burst, and the resulting mash is creamy, not gluey.

Add Butter Before Liquid: Stirring melted butter into cooked potatoes before adding cream coats their starch molecules and blocks them from absorbing water that would otherwise make them gummy. 

For extra-crusty exteriors on our roasted potatoes, we add a dash of baking soda to the water as they parboil. The alkaline environment breaks down pectin in the potatoes’ cell walls, causing their surface layer to fall apart and release starch that forms a pasty film. Then we further rough up their surface by tossing them with the fat and salt so that the pasty film thickens. When water in the film evaporates during roasting, the starch that’s left behind crisps and browns deeply.

As the red potatoes in our recipe simmer, they soften but remain largely intact because their plump, moist cells nestle closely together, creating a dense, silky-smooth texture. Cooking them long enough that they absorb as much moisture as possible maximizes this effect.