What sugar does in cake
Sugar grabs water and holds on. With less free water, flour proteins form less gluten, and egg and starch need more heat to set. The cake keeps rising longer and ends up with a softer, moister crumb.
Sugar keeps working after baking
Sugar keeps holding water after the cake leaves the oven, so a well-sugared crumb stays moist into day two. At the surface it browns through caramelization and reactions with proteins, giving a golden crust.
Test yourself
Questions from the interactive lesson, with the answer and the why.
A cake made with much less sugar comes out tougher and drier. Why?
More free water reaches the flour, and the batter sets sooner. More gluten forms and the structure sets earlier, so the crumb is tighter.
True or false: In a cake, sugar only adds sweetness, so you can cut it without changing anything else.
False. Sugar also softens crumb, delays setting, holds moisture and browns the crust.
What went wrong? You halve the sugar in a vanilla cake to make it less sweet. It bakes up pale, tight and dry.
Less sugar held less water and let the batter set sooner. Without sugar holding water, more gluten forms and the structure sets earlier.
Fill the blank: Sugar softens a cake because it ___ water that flour and eggs would otherwise use.
Sugar softens a cake because it binds water that flour and eggs would otherwise use. Bound water is not free to build gluten or help egg and starch set.
You want a cake that is still soft on day two. Which move helps?
Keep the full sugar in the recipe. Sugar holds water in the crumb after baking, so the cake stays moist.