It turns out that heating milk to 180 degrees Fahrenheit (almost boiling but not quite) causes a chemical reaction called denaturing. This process breaks down the whey protein of the scalded milk. For example, if the protein in some baking recipes isn’t modified in a dough, it can interfere with gluten’s interaction with the yeast. The heat dismantles the structure of the milk molecules, releasing peptides, amino acids and sugars, which the yeast feasts on (via Savory Experiments†
In addition to this necessity for proper yeast activation in a dough, hot liquids — including scalded milk — are excellent carriers for flavor. For example, infusing dairy with garlic for mashed potatoes or vanilla in custards makes for a tastier result. Warm milk can also help set the butter in a batter and speed up the rising process when making bread.
Be careful when boiling milk, because milk burns quickly. It too boils over quickly and is a hassle to clean up. Further, food network recommends lowering the heat of your milk to less than 139 F before adding the yeast or you’ll kill it.
Following this seemingly finicky process of boiling milk will yield significant results in baking, such as nuanced flavors and silky custards. In addition, Busby’s Bakery agrees that scalded milk makes a more tender crumb and lighter cookies.
