Coffee cake is cake intended to be eaten with, or flavored with, coffee. British coffee cake is a sponge flavoured with coffee. They are generally round and consist of two layers separated by coffee flavoured butter icing, which also covers the top of the cake. Walnuts are a common addition to coffee cakes. In the United States, coffee cake generally refers to a sweet cake intended to be eaten with coffee or tea (like tea cake).
Coffee cakes, as an accompaniment for coffee, are often single layer, flavored with either fruit or cinnamon, and leavened with either baking soda (or baking powder), which results in a more cake-like texture, or yeast, which results in a more bread-like texture. Sour cream is used in traditional American coffee cakes to both impart a tart flavor and activate baking soda used as a leavening agent.
Coffee cake, which can also be known as gugelhupf or kuchen, was not invented. Instead, it evolved from other sweet items. Sometime in the 17th century, Northern/Central Europeans are thought to have come up with the idea of eating sweet cakes while having their coffee. Because the countries in the area were already known for their sweet yeast breads, the introduction of coffee in Europe led it to be known that they were a great compliment to the beverage. Immigrants from countries such as Germany and Scandinavia had adjusted their recipes to their likings and brought them along with them to America. Though the cakes varied, they all contained ingredients such as yeast, flour, dried fruit, and sweet spices. However, over time, the coffee cake recipes changed as cheese, sugared fruit, yogurt, sour cream, began to be used. This is a result of the vast use of pasteurization in America following World War I, which also led to a new type of coffee cake to be created. This was called sour cream coffee cake.