Sweet potatoes or yams make a delicious and vitamin-filled mashed dish, especially when mixed with butter and spices like cinnamon. Cooking the healthier sweet potato is similar to cooking white potatoes, although the harder flesh of the sweet potato means it needs a longer cooking time. Like white potatoes, sweet potatoes can be baked or boiled before mashing, and each has its benefits. Note that what some areas of the United States call yams are really sweet potatoes; these are from a different genus than true yams, which are not the orange potatoes so common in fall foods.
Faster Boiling
One advantage to boiling yams or sweet potatoes before mashing them is that they cook a lot faster than if you bake them. Small pieces of sweet potato boil within about 10 minutes, if not less. Technically, the potatoes could bake just as fast as they boil if you cut them into small enough pieces, but that has its own disadvantages when mashing them afterward.
Skins
Baking sweet potatoes, even if you’ve peeled them completely, allows every exposed surface on each piece to thicken a bit and become almost like a second skin. Think of the thickened -- if not downright crispy -- sides of a peeled french fry. That thickness won’t go away when you mash the sweet potato pieces, instead mixing in, possibly in large pieces. Of course, if you like that thickness, then baking the potatoes first and mashing the “skin” in could be delicious. You can avoid this if you keep the real peel on and bake the sweet potato whole, but that takes much longer.
Water Saver
On the other hand, baking has a major advantage in that it doesn’t waste water. Usually the amount of water needed to cover the sweet potato pieces is more than you need to keep them moist while mashing them. Recipes tend to call for draining this water out, which means you lose a lot of water. It could be possible to save the water for use in soup, but you’d have to coordinate that menu to ensure you were making both dishes the same night -- once the water has bits of food in it, you can’t store it indefinitely.
Vitamin Loss
Vitamins can both be destroyed by cooking and leach out into water if you’re boiling food. So if you boil sweet potatoes, you could potentially lose more vitamins than you would if you just baked them. Heat destroys some vitamins, so you’ll have to deal with loss either way you go. If you still decide to boil the potatoes, save that water and, as with the water-loss issue, use the water in soup so you can still eat some of those vitamins.
