Baking – What purpose does coffee serve in a chocolate cake recipe

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I have a recipe for a chocolate buttermilk cake. It's not constructed like most cakes, but it's always turned out OK. I've always wondered what does the coffee in the recipe do?

Is the coffee just there as an additional flavor? (The cake never tastes strongly of coffee.) Can I use a cheap instant coffee, or will a higher quality coffee make a difference? Does the acid in the coffee do something? Does the temperature of the coffee really matter?

Here's the recipe:

3 cups flour, 2 1/2 cups sugar, 1 1/2 tablespoons baking soda, 1/2 tsp salt, 1 cup unsweetened cocoa powder, 1 1/3 cups vegetable oil, 1 1/2 cups buttermilk, 3 eggs, 1 1/2 cups freshly brewed hot coffee, 1 tablespoon pure vanilla extract

Slowly combine the flour, sugar, baking soda, salt and cocoa powder. Blend (on medium speed) in the oil and buttermilk. On low, mix in the eggs, one at a time. Add the hot coffee and vanilla and mix on low speed.

Divide into two 9 inch round cake pans and bake at 350° for 30-35 minutes.

from Caprial's Desserts by Caprial Pence and Melissa Carey

Best Answer

it's probably there to add depth to the flavor, since chocolate and coffee complement each other so well. i've used the instant kind in similar recipes and it's just fine.

Fat content of cocoa powder

You cannot simply replace the cocoa powder with flour, because it compared to flour, cocoa powder:

Contains more fat (about 10-12 percent by weight, for grocery store brands; more for some premium brands up to about 25%)
Is more acidic
Is far, far more flavorful (okay, that part is not desired in a white cake)

You should use slightly less flour than there was cocoa, to avoid adding flour by weight equivalent to the fat in the original recipe which would throw the balance off. I would suggest a half cup plus 2 tbls of flour instead of 3/4 cup of cocoa as a starting point.

Flavor balance

With the astringency of the cocoa removed from the recipe, the flavor balance may be too sweet. You might want to try reducing the sugar by about 1/4 cup - 1/2 cup.

Acid and Leavening

The original recipe contains both baking soda (which requires an additional acid from another ingredient) and baking powder as leavening.

When you remove the cocoa, you are removing the acid that the baking soda was intending to react with.

Therefore, you need to remove the baking soda, replacing it with baking powder which brings its own acid. You might need a slightly larger amount, as part of the weight of baking powder is the acid, so there is less leaving per unit than with baking soda. I would suggest an additional 1/2 teaspoon as a starting point.

Boiling water

The boiling water is specifically intended, I infer from experience with many chocolate cake recipes, to bloom the flavor in the cocoa. When you remove the cocoa from the recipe, you remove the need to use boiling water to enhance the chocolate flavor.

Furthermore, the reason water is used rather than milk or another liquid is to interfere less with the perception of chocolate flavor. Therefore, you may choose to use another liquid like milk or additional coconut milk which will enhance the flavor and tenderness of your final cake.

Vegetable Oil

Vegetable oil is chosen in this recipe to avoid interfering with the flavor from the cocoa.

You may continue to use it, or you may find that butter or even coconut oil give a more agreeable flavor for the final product you are creating.

Method

With all of the above changes, there will no doubt be some changes to the method. Since you have only listed the ingredients, and not the actual steps, it is harder to be specific here.

However, what will be left is a fairly standard sponge cake, so should modify the steps to the standard creaming method:

Sift the dry ingredients together; combine the wet ingredients other than butter and sugar
Cream the butter and sugar(s) together
Add in the eggs one at a time, beating until smooth.
Add the dry mix alternating two or three times with the wet mix, beating each time for 30 seconds or so
Beat one or two minutes longer to develop structure

Flavorings

For coconut, using coconut oil in lieu of vegetable, and more coconut milk in lieu of water, and adding coconut extract should do the trick. The recipe should also be able to carry a small amount of shredded coconut if you choose, although that will change the texture.

For vanilla, try butter and milk instead of oil and water. Add vanilla extract.

For lemon, start as with vanilla, and add lemon zest to the batter (and maybe lemon extract), and possibly, should you choose, a touch of yellow food color. I would not add lemon juice as it has a profound effect on the chemistry; instead I would make a nice lemon icing or glaze that has the tartness.

Conclusion

Despite all of the above, I would not try to convert a recipe that is specifically designed for chocolate to a white cake; too many aspects of the cake will change. Instead, I suggest finding a truly outstanding white or yellow cake recipe to use.

Baking – Wouldn’t this cake batter be too runny? Would the coffee affect the texture

Compare that recipe to this very similar one from Ina Garten (complete with handy video) Chocolate Buttermilk Cake. Watch her pour. No question, that is a wet batter. Apparently it works fine, Ina's recipe is very highly rated.

Both recipes use volumetric measurements (ugh), so I'll use cups.

Ina's recipe (sugar is wet (sort of), subject for another question) - Wet ingredients (2 + 1 + .5 + 1 + .5 (eggs) = 5 cups wet to 2.5 cups dry (flour plus cocoa) 5/2.5 = 2

Your recipe: Wet ingredients (2.5 + 1.5 + 1.33 + 1.5 + .75 (egg) = 7.58 cups wet to 4 cups dry (flour plus cocoa) 7.58/4 = 1.9

So they're very close, Ina's actually a bit "wetter".

I am not aware of anything special the coffee would do to the baking chemistry here. It's got some acid, but I don't think that is relevant. As far as the "wetness" of the batter, it's the same as water as far as I know. The temperature might help dissolve the sugar, but that would be a minor thing at best.