A couple of days ago I got an email from Ochen Kaylan , a producer of American Public Media’s Weekend America. He was gathering information about the differences between Sweet Potatoes and Yams, for a Thanksgiving show , and invited me to participate. We all know the sweet, sticky, gooey side dish that is loaded up with brown sugar, spices, lots of butter and the ubiquitous marshmallow topping. But people always wonder which to use, sweet potato or yam? Really what is the difference?
It turns out that sweet potatoes and yams that we find here in the States are really all sweet potatoes. What we think of as yams are called this by mistake. It started long ago when the slaves were brought over and identified sweet potatoes with the “nyami” from Africa. The name stuck and we’ve been eating a misnomer ever since. To further the complication, neither of them are really potatoes at all! They are both tubers, although not even related to each other. In fact, the sweet potato is a cousin of the morning glory flower. There are about 200 varieties of true yams, of which none grow in the States. They are all different colors and sizes, the largest measuring almost 7 feet!!! I was so hoping to find one of those.
Still confused at which one to use for Thanksgiving, we set off to find out what the differences are and how they will effect your recipes. I’ve baked, boiled, sauteed, mashed and grated them both, but until now I didn’t really know what I was dealing with. Our journey started at an Asian Market called Shuang Hur  on Nicollet Avenue in Minneapolis. They had bins filled with things that looked like sweet potatoes or yams, sort of. They weren’t orange or tan like I am used to seeing, but the shape suggested a relationship. They were black, white, red and some had rough, even “hairy” skins. The bins weren’t market so one of the employees acted as our guide through this exotic produce isle. It turned out they were authentic yams, not sweet potatoes at all. We bought a bunch and I headed home to bake them along with some sweet potatoes and “yams” I’d bought at Whole Foods  and my local coop.
This is what we found:
From top: Camote (sweet potato), Purple “ube” Asian Yam, Sweet Asian Yam, Yampi Yampi, Jewel “yam” (sweet potato), Sweet Potato, Garnet “yam” (sweet potato). In order to taste all of the varieties on an equal playing field we baked them. I like baking sweet potatoes and yams over boiling because it caramelizes the natural sugars and makes them more intense. These sweet tubers are not only tasty and beautiful but they are also packed with vitamins A & C.
Here is the flesh of the sweet potatoes. Both Ochen and I thought that the Jewel “yam” was the sweetest, then the Garnet “yam”, the Camote and finally the sweet potato was the least sweet of the bunch.
These are the authentic yams that we found at the Asian market. The purple “ube” yam was the sweetest of all the yams, sweet potatoes and fake “yams!” Its color was disarming and like no other natural food I’ve ever seen. It was delicious and I will definitely be buying more. The color alone had me, although I was disappointed in how it baked in the pots de creme (below). The Yampi Yampi was dry and mealy and not at all sweet. The sweet “yam” was creamy and sweet, but not compared to the purple yam. This one I have in “” because I couldn’t find any information on it and wonder if it isn’t a sweet potato?? If you know please tell me!
Our next experiment was to bake the different “yams,” sweet potatoes and real yams in a recipe. I was curious if the differences we detected in the plain baked version would hold true in a dish with other flavors competing with it.
First I made a Pots de Creme:
1 1/2 cups mashed sweet potato, purple yam or jewel “yam”
6 large egg yolks
1/4 cup honey
4 cups heavy cream
6 whole cloves
1/2 piece of peeled ginger
1 cinnamon stick
1 vanilla bean 
1/3 cup brown sugar
Preheat oven to 325°
In a heavy bottomed pan gently heat the cream with the ginger, cloves, cinnamon, vanilla and brown sugar. Allow to gently simmer and then turn off heat. The longer you allow the cream and spices to steep the more intense their flavor will be. This can even be done the day before. When ready to prepare the custard strain the spices from the cream.
Add the yolks, honey and mashed sweet potato to the cream. With an Immersion Blender  or whisk blend everything together very well. I like to use the immersion blender because it further breaks up the potato. If you are not using one, you might want to strain the custard before putting in the cups and baking.
Neither Ochen nor I could detect any difference between the pots de creme using the different varieties of yams and sweet potatoes. The color of the purple yam mixed with the egg yolks turned the whole thing a tinge gray and it had the slightest graininess to the texture, so I’d not use it for this again.
For the second recipe I decided to use grated sweet potatoes and yams to see if the flavor would be enhanced. Otherwise the list of ingredients are quite similar.
The result was surprising. Unlike the pot de creme we really could taste a difference between the different varieties and it wasn’t all that subtle. I guess leaving it raw and coarsely grated made the difference.
This is an old recipe for sweet potato pudding that is meant to be served with whipped cream spiked with Jack Daniel’s whiskey. It is important that all the ingredients are at room temperature.
Tennessee Old Maid’s Sweet Potato Pudding from Classic Home Desserts: 
1/4 cup (1/2 stick) unsalted butter
1/2 cup packed brown sugar
1/4 cup sugar
2 large eggs, beaten
1 teaspoon ground cinnamon
1/4 teaspoon fresh grated nutmeg
1/4 teaspoon ground clove
2 1/2 cups coarsely grated raw peeled sweet potato, purple yam or jewel “yam,” well packed
1 1/2 cup warm half&half or whole milk
Preheat the oven to 350°
Cream together the butter and sugars until well blended and very light. Beat in the eggs; beat in the spices and salt. Stir in the sweet potato or yams; add the milk and mix thoroughly. At this point the mixture may appear to separate, but proceed because it doesn’t seem to effect the finished pudding.
Bake until set, about 25-30 minutes. Cool to room temperature and serve with whipped cream that you spike with Jack Daniel’s. I tended to like this pudding made with the sweet potato and Ochen liked with best with the super intense purple yam. You try and decide with you like best!
Here are more recipes to make with sweet potatoes or “yams” or real yams!
Vegetarian Cooking for Everyone  by Deborah Madison has a Sweet Potato Souffle
Suvir Saran’s American Masala: 125 New Classics from My Home Kitchen 
has a recipe for spicy Sweet Potato Chaat that will make you weep.
Lynne Rosetto Kasper and Sally Swift have a recipe for “Yams” with Ginger and Scallions in their book The Splendid Table’s How to Eat Supper: Recipes, Stories, and Opinions from Public Radio’s Award-Winning Food Show 
A Southern baking bible Biscuits, Spoonbread, and Sweet Potato Pie  by Bill Neal has amazing recipes for Sweet Potato Pie and Biscuits.
Irene Sax wrote an article recently for Saveur magazine  with a classic Sweet Potato Casserole.
Finally the quintessential candied “yam” recipe from Mark Bittman’s How to Cook Everything , albeit a healthier version.
Jeff and I have also been working on some recipes for our follow up book to Artisan Bread in Five Minutes a Day  that include sweet potatoes, maybe now I will throw in a yam recipe as well?
Due to the fact that I now have about 10 pounds of baked sweet potatoes and yams my family is eating them with everything. I just made a Sweet Potato Milk Shake that I just have to share with you.
1 cup baked sweet potato of your choice (I used jewel “yam”)
3/4 cup whole milk
3 cups extra rich high premium vanilla ice cream of your choice
2 tablespoons maple syrup
1/2 teaspoon ground cinnamon
1/8 teaspoon ground ginger
1/8 teaspoon fresh ground nutmeg
1/8 teaspoon ground allspice
2 tablespoons bourbon (optional)
Mix well in a blender and split between 2-4 cups. Seriously fabulous, like a cold creamy sweet potato pie!