Not salting the water.
Like pasta, potatoes absorb the water they're cooked in. Leaving it out means you're starting off with bland potatoes. Follow this tip: Begin the process of seasoning your mashed potatoes by adding salt to the water when cooking the potatoes.
Once there is too much starch in your mashed potato mixture, the texture will quickly turn from fluffy to gummy. Instead of using an electric hand mixer, food processor, or blender — all of which will overwork the potatoes — use a ricer, food mill, or hand masher to gently break down the spuds, per The Spruce Eats.
The problem with overcooked potatoes is that they absorb a ton of water. When you go to mash them, they'll be soupy and sad. One way to fix them is by placing them in a pot over low heat and gently cooking them. The excess water will turn into steam, and your mash will dry out.
You could be using the wrong potatoes. Potatoes are generally considered "waxy" or "starchy." Waxy potatoes (like white potatoes and red potatoes) are more prone to gumminess when mashed, as opposed to starchy potatoes (like Yukon Golds and russets).
SEBAGO: A long to oval shaped all-rounder with white flesh and skin that's common in supermarkets and green grocers around Australia. This potato is great for boiling, mash, roasting, baking, chips and mash.
A word about butter: Don't melt butter before stirring it into the potatoes because the milk solids and fat will separate. You can add cold butter to your hot potatoes since the butter will melt as a whole and distribute the fat and milk solids evenly.
If your potatoes have been growing in very dry soil, the potatoes themselves will have a fairly low moisture content when harvested. What this then means is that when the potatoes are build they absorb more water and fall to pieces quite quickly.
Tips for the Best Mashed Potatoes
Start cooking the potatoes in cold water: This ensures that the potatoes cook evenly. Otherwise, if you start with hot or boiling water, the outsides of the potatoes cook and soften while the middles are still hard and crunchy.
To thicken mashed potatoes, you can add a thickening agent like cornstarch, flour, powdered milk, or tapioca. Add one tablespoon at a time until you reach your desired consistency. You can also add heat, more potatoes, or even strain the mashed potatoes in order to reach your desired consistency.
Here's how to do it: For every pound of potatoes in your mash, drizzle 1 tablespoon of melted butter over the dish and fold it gently into the potatoes. If the mash is still too gluey for your liking, repeat the process with another tablespoon of butter.
Soupy, watery mashed potatoes usually happen because the cooked potatoes were cut into pieces that were too small, weren't drained well enough, or were overcooked. Fix them: Scoop the watery mashed potatoes into a pan and stir constantly over low heat to evaporate the excess liquid.
You shouldn't let butter be the only dairy you use, however. Consider adding half-and-half or heavy cream and a bit of sour cream (even goat cheese) to get the best flavor and creamiest texture every time, like in these Best Mashed Potatoes.
Swap Out the Water
In fact, when you mix the potato flakes with the warm broth, the result is a creamier, more buttery-tasting bowl of spuds. You can also swap milk or half-and-half for the water required.
Heavy cream will make for the creamiest mashed potatoes, but whole milk or half and half will also work. Don't use anything with less fat than whole milk, otherwise, your potatoes won't be as flavorful or creamy.
Tip #4: Never try to mash up cold potatoes. It has to do with some chemical-y thing with the starch. If your potatoes go cold, heat them up again (in warm water, a microwave) and then try to mash them.
“Salting the water not only seasons the potato, but it also allows it to boil to a hotter temperature. This in turn cooks the potatoes' starch more thoroughly, resulting in a more creamy texture [for mashed potatoes],” says Sieger Bayer, Chef and Partner at The Heritage.
Potatoes can be peeled prepped and cut into water up to 2 days before boiling for mash.
Bring the water to a boil. Reduce heat to medium low. Cover the pot with a lid and let simmer until fork-tender, about 10-15 minutes for small and/or cubed potatoes or 20-25 minutes for large potatoes. Drain and cool.
If keeping potatoes in water for more than an hour, refrigerate. However, don't soak them any longer than overnight—after that, the potatoes start to lose their structure and flavor.
Soaking potatoes in water helps remove excess starch. Excess starch can inhibit the potatoes from cooking evenly as well as creating a gummy or sticky texture on the outside of your potatoes. Cold water is used because hot water would react with the starch activating it, making it harder to separate from the potatoes.
Do NOT add cold liquid. Make sure the milk or cream you add to your potatoes is HOT. This helps it absorb better so you don't feel the need to overmix. Overmixing is bad.
Melted or liquid butter will thin out your batter, giving you ultra-flat cookies or cakes that are dense and uneven.
But the most essential suggestion, per Bon Appétit, is always to salt the water you are boiling your mashed potatoes in. It acts as pre-seasoning, and Bon Appétit recommends adding a full cup of kosher salt to the boiling water.