Caramelised Onions: The Time Requirement

López-Alt's testing of caramelised onion technique produced one of his most cited findings: properly caramelised onions take 45–60 minutes minimum, not the 10–15 minutes claimed by most recipes. The shortcuts — baking soda, high heat, added sugar — produce different results that are faster but not equivalent. Understanding what is actually happening during the long slow cook explains why shortcuts fail.

Onions cooked in fat over medium-low heat for 45–60 minutes until deeply browned, sweet, and reduced to approximately one-fifth of their original volume. The transformation involves water evaporation (the onions lose 75–80% of their weight as moisture), sugar development, and Maillard browning — all of which require time.

Properly caramelised onions provide a sweet-savoury depth that raw, sautéed, or quickly browned onions cannot replicate. They are the foundation of French onion soup, the base of a great burger topping, the soul of a tarte aux oignons. The time investment cannot be bypassed without producing a categorically different ingredient.