It’s not that strange, if you think about it. But to explain why, we need to talk about gluten a bit more.
Close-up of wheat by Bluemoose, on Wikimedia Commons (CC license)
In wheat and some of its relatives (like barley), there are a number of proteins that are linked together with (water-soluble) starches; most of those proteins are either (alcohol-soluble) gliadin or glutenin (soluble in acid or alkaline). When you add water to flour, the starches dissolve, and the proteins start to cross-link, forming a stretchable substance that sticks to itself and we call by the Latin name for glue: gluten.
We’d previously discussed this kind of cross-linking of polymers in starch alone in the post for Yesterdish’s potato puffs. But while cross-linking of starch polymers in potatoes is never good, in wheat, it’s immensely important.
If yeast dough didn’t develop a polymer structure of some kind, it couldn’t rise–the gas bubbles would just float up and the bread would collapse under its own weight. Plus, the presence of gluten is what gives bread that chewy texture you crave in a baguette. To help achieve it, you can do certain things to encourage gluten development, like use a very wet dough that washes away starch faster, or kneading the dough for a long time, forcing the protein and starch bonds to break through brute force.
But what if you had a dough that you didn’t want to be chewy? Like, say, something you wanted to be very tender, and something that didn’t need yeast to rise?
Chocolate potato cake by Andrea Guerra, on Flickr (CC license)
Some amount of gluten formation is inevitable in wheat-based doughs; once you get the flour wet, the starches start to wash away and the proteins will start to link. But we know we can avoid some gluten formation by mixing less. Another thing we can do is use very fine, lower-protein flour, like cake flour or pastry flour.
But if you really want to minimize gluten to get the most tender, lightest, softest cake imaginable, you can substitute out some of the wheat flour for something else. We talked about using cornstarch for some amount of flour in the posts for Jiffy Cake from River Forest, Illinois and in Yesterdish’s vanilla cupcakes. (In particular, check out the Jiffy Cake for a political reason for flour substitutes.)
But you know what else is gluten free? A potato. The richness, creaminess, and delicate texture of a potato enhance a cake, and if the cake has a strong enough flavor–like, say, chocolate and raisins–you wouldn’t know it was there. And that isn’t new. Consider this version with slightly different proportions from the May 25, 1909 edition of the Goshen (Indiana) Daily Democrat:
Chocolate Potato Cake.
One cup butter, one and a half cups sugar, half cup milk, three eggs, two cups flour, two teaspoonfuls baking powder, three-quarters teaspoon each cloves, allspice and cinnamon, two tablespoonfuls chocolate, one cup grated boiled potatoes, raisins and chopped nuts as may be desired. Bake for about an hour.
From the box of Evia Marie Sands of Louisville, Kentucky.
Chocolate Potato Cake
1/2 c. butter
1 c. sugar
1/2 c. mashed potato
1/3 c. milk
1 tsp. baking powder
1/2 tsp. baking soda
1/2 c. cinnamon
3-1/2 Tbsp. cocoa
1 c. flour
1 cup nuts
1 cup raisins]
Cream 1/2 cup butter. Add 1 cup granulated sugar; cream.
Add 1/2 cup freshly boiled and mashed potato (the potato should be free from lumps).
Add one by one, beating after each addition, 2 eggs. Add 1/3 cup sweet milk.
Sift tsp. baking powder, 1/2 tsp. baking soda, 1/2 cup cinnamon, 3-1/2 Tbsp. cocoa, 1 cup flour. Sift three times.
1 cup nuts, 1 cup rasins.
Cook full 1 hour.