Why cooked onions turn sweet
Cutting an onion breaks its cells, so an enzyme meets sulfur compounds and makes the sharp, tear-causing gas. That gas is the raw bite. Heat destroys the enzyme and mellows the compounds that are left.
Slow heat concentrates the sugar
Onions are about 5 percent sugar. Cook them slowly over medium-low heat for 30 to 45 minutes. The water evaporates, the sugars concentrate and brown, and the onions turn deep golden and sweet.
Use a wide pan and a splash of water
Use a wide pan so steam can escape, or the onions steam instead of browning. If the bottom starts to scorch, add a splash of water and scrape. The browned film dissolves into the onions.
How to caramelize onions
Keep the heat medium-low and stir every few minutes. Onions go from pale to golden to deep brown over 30 to 45 minutes. If it took only 10, they browned fast but never got that jammy sweetness.
Test yourself
Questions from the interactive lesson, with the answer and the why.
A raw onion is sharp, but a sautéed one is mild. What happened to the sharp compounds?
Heat broke them into milder compounds. Heat changes the sharp compounds into milder, sweeter-tasting ones.
True or false: Onions cooked slowly lose water, so their flavor gets more concentrated.
True. Water evaporates as onions cook, leaving the sugars and flavor in a smaller volume.
Fill the blank: When onions cook, ___ is driven off, which concentrates the sugars.
When onions cook, water is driven off, which concentrates the sugars. Water evaporates, which concentrates the sugars and makes onions taste sweeter.
What went wrong? You crank the heat to caramelize onions faster. They turn dark and taste bitter.
The heat was too high. High heat burns the sugars before they can brown slowly.
Quick onions vs slow onions
Patience, measured in sweetness.
Do the 40-minute experiment
