My Goals

  • Quick start

  • Deep color and intense flavor

  • Extra sweetness

With nothing more than heat and time, onions can undergo an extraordinary transformation. Sweet and complex caramelized onions can improve everything from soups, dips, and sandwiches to pizzas, casseroles, pastas, and salads. The traditional approach is long, careful cooking over a low flame for upwards of 1¼ hours. There are shortcut recipes that rely on cranking up the heat, but the results are never as richly flavored as the real deal. I’ve also found that when I cut one of these quick-caramelized strands in half, I reveal a pale, watery interior lurking beneath the brown exterior. I set myself the challenge of finding a way to shave off time and still produce exemplary caramelized onions.

First, I reviewed the science behind the traditional approach: Cooking causes the onions to break down and soften, releasing water, sugars, and proteins. The water evaporates, concentrating flavor. Given heat and time, the sugars and proteins undergo two reactions. One is caramelization, in which sugar molecules recombine into hundreds of new flavor, color, and aroma compounds. The other is Maillard browning, where sugars react with amino acids to produce a different diverse array of flavors and colors.

Caramelizing onions the traditional way can take well over an hour. Could we find a way to reap the same benefits in a fraction of the time?

In the test kitchen we often turn to baking soda to speed up browning. This is because it creates a high-pH (basic) environment, which allows browning reactions to occur more readily. It’s also handy for softening vegetables because altering the pH helps weaken their structure. I wanted to speed up both processes, so why not add baking soda here?

I sliced three large onions and added them to a nonstick skillet (its surface would ensure that the fond stuck to the onions, not to the pan) with 2 tablespoons of oil and ⅛ teaspoon of baking soda. After just 45 minutes over a moderate flame, they were impressively browned, sweet, and complex-tasting. In fact, they were much sweeter than any I’d had before. Our science editor explained that the baking soda sped up the conversion of flavorless compounds called inulin into the simple sugar fructose. So while many recipes for caramelized onions call for adding sugar or honey to boost sweetness, there was no need for that in my recipe.

To find a faster path to caramelization, we first needed to understand how altering the onions’ pH affects browning and cell structure. To do that, meticulous note-taking was in order.

But there was a drawback to the baking soda. It caused the onions to break down too much; by the time they were browned, I had a skillet full of onion jam instead of the tender, distinct strands I wanted. To keep the flavor benefits of baking soda without ending up with mush, I added it at the last minute. Doing so, even at the last minute, deepened the color and flavor. But I still had to cook the onions for well over an hour. I’d have to look for other ways to speed things up.

Here’s the thought that came to mind. Moisture is usually regarded as the enemy of browning, since food needs to rise above 212 degrees in order to brown, and that can’t happen until most of the moisture burns off. But I knew that adding water and covering the skillet could help speed up the cooking without working against me. After all, the first part of the cooking process isn’t about browning but rather softening the onions and breaking down their structure. Surrounding the onions with steam (and submerging some of them in the added water) would heat them more quickly and thoroughly than just relying on the heat generated by the cooking surface of the skillet alone. When cooked with ¾ cup of water, the onions wilted about 10 minutes faster. I then uncovered the skillet and turned the heat to medium-high. Since browning occurs only where the onions are in direct contact with the hot pan, I gently pressed the softened onions into the bottom and sides of the skillet to allow for maximum contact. I let them sit for about 30 seconds and then stirred them; I repeated the pressing and stirring process for the rest of the cooking time. Repeating this technique thoroughly softened and deeply browned the onions in just 15 minutes; start to finish, the entire cooking time took less than half an hour.

To speed up the cooking process in a fraction of the time, we turned to an ingredient that you might think would be counterproductive: water.

There are countless ways to use these tender, sweet, richly flavored onions, and I came up with just a few: I combined them with sour cream, yogurt, chives, and vinegar for a quick dip; I layered them on puff pastry with tomatoes and goat cheese for an elegant tart; and I tossed them with pasta, pepper, and salty Pecorino. And that’s just a start.

Keys to Success

  • Quick start

    Starting the onions over high heat in a covered skillet with ¾ cup of water causes them to soften and start browning in just 10 minutes instead of the usual 15 to 20 minutes of traditional recipes.
  • Deep color and intense flavor

    Uncovering the skillet, reducing the heat to medium-high, and gently pressing the onions into the bottom and sides of the skillet ensures that the onions undergo the browning reactions that create the characteristic burnished color and complex flavor of caramelized onions. The flavors concentrate as the water evaporates.
  • Extra sweetness

    Finishing with baking soda boosts the onions’ sweetness—without the sugar or honey called for in many recipes—by encouraging the breakdown of flavorless inulin into sweet fructose.