You know you’re on the right track if your most trusted recipe sources agree on procedures for classics such as this one. This recipe for dulce de leche, a thick caramelized milk sauce essential in South American desserts, is adapted from Alton Brown, Saveur, and Wayne Gisslen.
While the instructions and cooking times differ slightly, all three sources agree on the use of baking soda, a key ingredient which may be a bit unexpected. The baking soda tips the slight acidity of milk towards alkalinity. This is important for two reasons (excuse me while I put on my lab coat):
- Alkalinity keeps milk proteins from curdling
For the same reason adding vinegar to milk makes cheese, mildly acidic milk, along with heat, may cause grittiness when milk proteins solidify. Adding the baking soda controls curdling to a certain degree, giving you a smoother dulce de leche.
- Alkalinity helps with browning
Since dulce de leche is all about caramelization, a little help with getting that deep brown hue can’t hurt. One reason pretzels and bagels are boiled in a lye solution is the alkalinity of the liquid — it helps brown the crust while baking.