Sugar: The Metabolic Accelerant
Sugar is viewed by many purists as a "cheat." But biologically, it is simply high-octane fuel. While flour starch must be broken down by amylase before the yeast can eat it, sugar provides an immediate, ready-to-eat feast.
Milk: The Chemical Softener
Water is neutral. Milk is complex. By swapping water for milk (as in Shokupan or Sandwich Bread), you introduce three new variables: Fat, Protein (Casein), and Sugar (Lactose).
Butter: The Gluten Lubricant
Butter is the bridge between bread and pastry. In small amounts, it softens. In large amounts (like Brioche), it transforms the dough into a foam-like structure that is more air than wheat.
Olive Oil: The Lipid Softener
Sourdough is traditionally lean (Flour, Water, Salt). When you introduce a lipid like Extra Virgin Olive Oil, you are entering the territory of "Enriched Dough." You are trading some crust crispness for crumb tenderness.