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The Science of Purée: How to Make Homemade Mashed Potatoes

The Science of Purée: How to Make Homemade Mashed Potatoes

A not-to-miss guide for the perfect potato purée: from ingredients to the cooking techniques, find out how to make homemade mashed potatoes.

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The kitchen is a magical place, where marvellous spells can be created, and well-established beliefs can be undone. Both events often occur when making a purée. But are you sure to know how to make homemade mashed potatoes? While it’s true that the modest potato can be transformed into one of the tastiest of dishes, the idea that making them well is easy is a commonly-held belief that should be re-evaluated. A great dish of mashed potatoes takes a great deal of attention in order to turn out perfectly: I’ve learned this personally, after years of attempts that I considered more or less adequate, I’ve discovered the tricks and secrets to making this beloved side dish, so here is my guide explaining how to make homemade mashed potatoes.

The first secret is in the main ingredient – the potatoes – which are rich in starch. Starch itself contains 20% amylose and 80% amylopectin – two words that may be unfamiliar, but should be understood if hoping to really master the art of the homemade mashed potato. Their main feature is that neither one of them mixes well with water: amylose will melt if the water is above 55°, while amylopectin is totally insoluble. This is why, when we mash the potatoes and add hot water, the amylose tends to ment, while the amylopectin takes on a disordered structure, rendering the mixture pasty and puffy – nothing like the velvety texture that we want to find on our plates. This is why instant mixes that require the addition of water, are incomparable to the homemade versions. With milk, however, the result is different, as milk is rich in a protein called casein, which makes the mixture more fluid and compact. And when casein is combined with fat, its structure becomes even more ordered, which improves the quality and taste. This is why any mashed potato recipe worth consulting calls for the addition of butter, as it provides the needed fat. To this end, olive oil could also be used, although that would mitigate the typical milky aftertaste.

Now we’re ready to cook. Naturally, we begin with the potatoes: while the exact variety isn’t important, they should be floury. Bring a large quantity of salted water to a boil and then add the potatoes. Once their tender, turn off the heat, drain and peel the potatoes. Make sure you work quickly, as the potatoes should stay as hot as possible: dice them, put them in a potato masher and reduce them into a smooth pulp. Pour the mixture into the same pot used to boil the potatoes (since it’s still warm, it will speed the process) and then place on a burner over low heat. Mix everything with a wooden spoon for a minute, then add chunks of butter, still stirring. Once the butter is melted, add the hot milk (best if fresh and whole), just a bit at a time, stirring continuously. 120 grams of butter and 300 ml of milk are enough for every kilo of potatoes, but use more or less in order to obtain the desired consistency.

When done, add salt and a bit of grated nutmeg. To finish, a dash of grated cheese (although traditional recipes don’t call for it). Now that you know how to make homemade mashed potatoes, you can serve a delicious dish of warm potato purée: although in the summer months it can also be enjoyed cold. Once chilled, in fact, we can add a bit of soy sauce or chives and serve it as a delicious finger food. This is a great way to use up leftover mashed potatoes – although if you originally intend to serve it cold, it’s best to use olive oil instead of butter.

Still interested in Food Science? Don't miss our focus on the Science of Sauces, the Science of Fried Eggs, and the Science of Meat: you'll find some gourmet tips to apply science and physics in your kitchen!

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