Caramelized onions are one of those ingredients you can add that immediately makes any dish feel a little fancier. They have that delicious savory-sweet combination, they're great in almost anything, and they're surprisingly easy to pull off at home. So why don't more people make them?
They take freakin' forever.
The depth of flavor in caramelized onions comes from cooking for a long time over low heat. It allows the sugars to release and caramelize slowly rather than burning. As they cook, the sugars break down into different compounds, which is why caramelized onions have such a complex flavor profile.
Most of the time, caramelizing onions properly takes around 45 minutes, sometimes even longer. What if I told you it was possible to cut that process down to as little as 15-20 minutes? You'd probably give it a try, right?
J. Kenji López-Alt from Serious Eats found that adding a pinch of baking soda helps onions to caramelize much faster by raising their pH level. A higher pH level speeds up the Maillard reaction, which is responsible for the browning of the sugars in food. It can increase the browning rate by over 50%, and it doesn't take much—about 1/4 teaspoon of baking soda per pound of onions is all you need.
Others, however, recommend using only a pinch of baking soda and no more—blogger Brenda J. Wiley found that using just 1/8 teaspoon to caramelize three large onions altered the taste in an undesirable way.
Some people like to add a bit of sugar to the onions while they cook to increase caramelization and to counteract any potential bitter aftertaste from the baking soda, but plain sugar doesn't really speed up the process, it just makes them sweeter. Lopez-Alt caramelized his sugar before adding the onions and took another 5 minutes off the total process.
Check out his full guide over on the Food Lab for details on the best onions to use, how caramelization works, and more tips for making the process faster.