By Harold McGee
Because it contains concentrated protein and sugar, sweetened condensed milk will “caramelize” (actually, undergo the Maillard browning reaction) at temperatures as low as the boiling point of water. This has made cans of sweetened condensed milk a favorite shortcut to a creamy caramel sauce: many people simply put the can in a pot of boiling water or a warm oven and let it brown inside. While this does work, it is potentially dangerous, since any trapped air will expand on heating and may cause the can to burst open. It’s safer to empty the can into an open utensil and then heat it on the stovetop, in the oven, or in the microwave.