How Starch Content Affects Cooked Texture
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.