Starch and potatoes
There’s a lot more to potatoes than meets the eye, and the choice of which potato to use in a recipe can have a huge impact on the results. The most important variation comes in the form of starch, the long, sometimes branched chains of bonded sugars that store energy in potatoes and most plants. In the kitchen, we know that it thickens pastry cream and helps cookies set, and it also plays an important role in the texture of this soup.
When the starch granules in the potatoes encounters hot water, they take in water and swell. If they cook long enough or if you beat them up, the granules burst and release individual starch molecules into your cooking liquid. Too many of these long, sticky strands form a network that holds the soup together–also known as making it into too-thick, sticky glue.
I originally made this soup with russet potatoes, but it all went downhill once I brought out the immersion blender. It tore apart the swollen cooked starch granules in the potatoes and I became all too familiar with the gluey soup situation. Luckily, a simple switch made a big difference: Yukon gold potatoes have lower levels of starch, leading to less bursting, less networking, and less stickiness. I made the two side by side and the Yukon golds made a creamier, finer-textured soup without the problematic starch breakdown of the russets.
Starch information from Shirley Corriher’s CookWise.