Browning
How to caramelize onions (and how long)
Caramelized onions take time: thin slices, medium heat, steady stirring. How long it really takes, and when a pinch of baking soda helps.
Published
01
What
According to the National Onion Association, onions release moisture and their cells break down and soften as they cook. Sugars are released, and as they heat, both caramelization and Maillard browning create the dark golden brown. The first stage is mostly about water leaving the pan. The browning comes after.
That’s why this can’t be rushed on high heat: the outside scorches before the inside has softened. For the browning chemistry itself, see the Maillard page.
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Why (ELI5)
ELI5
A pinch of baking soda raises the pH, which speeds up Maillard browning and also softens the onions faster. The National Onion Association tested 1/8 teaspoon on 1 pound of sliced yellow onions with 2 tablespoons butter over medium heat, and the onions were soft and caramelized in about 13 minutes. It notes that more than about 1/4 teaspoon per pound can give an unappealing chemical-like taste.
The trade-offs, from the same test: the onions turned creamy, almost like an onion jam, so they suit blending into dips or spreading on a sandwich, but not a pizza topping where you want some bite. The pan got messier, with very dark sides, so a nonstick pan helps with cleanup.
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How
Pick the onions and the pan
Illinois Extension says any onion will do, but yellow onions caramelize nicely. Slice them about 1/8 inch thick: thicker takes forever, and thinner dries out and burns. Use a bit of oil, which has a higher smoke point than butter, or a mix of the two. Unless your skillet is bigger than 12 inches, cook only two large onions at a time.
Heat, stirring and time
- 01Slice yellow onions about 1/8 inch thick.
- 02Heat a little oil (or oil and butter) in a wide skillet over medium heat and add the onions.
- 03Cook, stirring every 3 to 5 minutes. Drop to medium-low if they brown before they soften.
- 04Keep going until they’re dark brown and soft but not mushy.
Use medium or medium-low heat, which Illinois Extension calls the temperature that caramelizes the sugars without burning them. Stir every 3 to 5 minutes, and don’t walk away for long.
How long? Illinois Extension says it may take 30 to 40 minutes to reach a dark brown color and a soft but not mushy texture. The National Onion Association says truly caramelized onions take around 45 minutes, sometimes longer, and its own recipe says up to 45 minutes over medium heat in a 12-inch skillet. So plan on 30 to 45 minutes, and go by color and softness rather than the clock.
When the pan gets brown
The browned bits left on the pan are fond, the same thing that starts a pan sauce. A splash of liquid and a scrape with a wooden spoon loosens them so you can stir them back into the onions.
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