Because nobody likes runny mashed potatoes. 

By Corey Williams
July 01, 2020
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Never fret over a batch of “ruined” mashed potatoes again. Here’s everything you need to know about thickening runny potatoes:

Why Are My Mashed Potatoes Runny? 

There are quite a few reasons your mashed potatoes are watery. If you’re staring down at a bowl of white liquid and wondering what went wrong, ask yourself these questions:

  • Did I use soggy potatoes? It’s essential to drain and dry your potatoes well after you’ve cooked them in water. If you don’t, all that excess moisture will have nowhere to go once you start mashing. 
  • Did I use just one kind of potato? Waxy (Yukon gold) and starchy (Russet) spuds both play important roles in making the perfect mashed potatoes. Use them together instead of relying on just one variety. 
  • Did I use too much liquid? This is an obvious issue. Make sure to read your recipe well and use the proper ratio of milk or cream to potatoes.  

No matter how they happened, there are a few simple ways to fix your runny potatoes: 

1. Add a Thickening Agent 

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This is the most common, and perhaps the simplest way, to thicken mashed potatoes. You can use what you have on hand: Flour, cornstarch, or powdered milk are all solid options that are probably already in your pantry. 

For what it’s worth, we recommend sticking with cornstarch—it has twice the thickening power of flour and it’s safe for gluten-free diets. 

Stir in the thickening agent gradually, about a tablespoon at a time, until the potatoes have reached your desired consistency. 

2. Use Heat to Your Advantage

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You can also thicken your mashed potatoes by continuing to cook them on the stove. Heat draws the excess moisture out of runny potatoes, leaving you with a denser finished product. 

This is a risky move, though, as overdone mashed potatoes are gummy and unpleasant. Make sure to keep a close eye on them if this is the method you choose. 

As they cook, stir every so often so they don’t stick to the bottom of the pot. But don’t stir too much! Overworking is another way to ruin the potatoes’ texture. 

If your stove is full, you can use the oven to accomplish the same thing. Just place the potatoes in an uncovered, oven-safe casserole dish and heat them for about 10 minutes at 325 degrees. 

3. Add Dehydrated Potatoes 

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Last but certainly not least is this tip from Dr. Potato at IdahoPotatoes.com (we literally cannot think of someone with more authority on this subject): An “easy fix for watery potatoes is to break out the instant dehydrated potatoes and mix them in a tablespoon at a time, into the wet potatoes. This usually will thicken them up.” That’s right—you can thicken potatoes with potatoes!