It's really tempting to reduce the sugar in a cake recipe. The average vanilla layer cake recipe is made with at least one cup of granulated sugar. A whole cup of sugar to make two layers of vanilla cake does seem like a lot, but that sugar does more than just sweeten the cake layers. Here are the most important ways sugar impacts your cakes.
The most obvious role sugar plays in a cake is to sweeten it, which also helps enhance or bring out some flavors and suppress others, making desserts baked with sugar more appealing.
Moisture and Tenderness
Sugar is hygroscopic, meaning that it absorbs water, and by doing so, it helps prevent your cakes from drying out when you store them. Without sugar, your cakes would go stale much quicker. The presence of sugar in a cake batter also interferes with the formation of gluten, preventing those proteins from arranging into a network. Less gluten formed means a softer, more tender cake with less "chew." Chewy bread is great, but chewy cake? Not so much.
GBD (Golden-Brown Delicious)
If you've ever baked something with little to no sugar in it, you've probably noticed that it didn't brown much (unless you left it in the oven for a long time). Sugar is essential to two key processes that contribute to the flavor and appearance of the cake crust: caramelization and Maillard browning. Caramelization occurs when sugars are subjected to high heat (around 340°F), which transforms them into various flavorful, golden-brown compounds. Maillard browning happens at lower temperatures than caramelization, and requires the presence of proteins (from milk, flour, or eggs), which react with sugars to produce complex brown compounds. Whenever caramelization and Maillard browning occur, those colored compounds that form also change the flavor of the crust, leading to a more complex flavor in the crusts of cakes, with caramel, toasted, and nutty notes.
To make a cake batter, the first step is usually to cream the butter with the sugar, beating them together for several minutes. This step aerates the butter, lightening it and incorporating lots of tiny air bubbles and pockets that will make your cakes lighter and more spongy. The same goes for foam-based cakes (like génoise and sponge cakes), where the eggs are whipped with the sugar. The eggs lighten with the tiny bubbles that form as you whip the mixture, and the sugar helps stabilize the foam as it forms. Sugar helps you get air into cake batter.
When you list off all the roles that this one seemingly simple ingredient plays, you can imagine how reducing the sugar in a cake recipe can greatly impact how the recipe turns out. It's understandable why most recipe writers don't recommend to reduce the sugar in cake recipes.
Are there any extra steps you take, or substitutions you can recommend, for successfully reducing the amount of sugar in a cake recipe?