The Onion Project

A peculiar fascination with alliums had been long simmering within. It started with the taste of Alive and Radiant’s Sweet Onion Veggie Krunch. I’d never knew onions could be so… sweetly concentrated. Onions were on the menu again in multifarious forms during execution of the recipes in Fundamentals of Raw Cuisine: pine nut parmesan, caramelized onions. flatbread pizza crust. A common theme amongst these is dehydration, that is slow evaporation of moisture at low temperature to concentrate flavors. It sparked the curiousity the find out the best method to achieve caramelized onions. The Onion Project, launched.

The Onion Project Summary

Part 1: To test different methods of caramelizing onions and the effect on taste, texture and appearance.
Part 2: To use caramelized onions in recipes

  1. French onion soup
  2. French onion dip
  3. Onion bread
  4. Onion tart


Onions belong to the odiferous allium family which also includes garlic, scallions, chives and leek and similar ilk with concentric rings. They are rich in organosulfur compounds which are responsible for their smell, tear-inducing effects and healthful benefits. Caramelized onions are achieved by slowly cooking down raw onions. During this process, two reactions occur – the Maillard reaction and caramelization.

The Maillard reaction is a non-enzymatic reaction involving the reaction of simple sugars and amino acids and contributes to aroma, taste and browning. The chemistry underlying the Maillard reaction is very complex. It is not just one reaction pathway but a network of complex reactions. It is mostly studied within the context of baked goods and breads. In essence, the carbonyl groups of sugars react with the amino groups of amino acids in the food, rearrange form many arcane intermedite products, and eventually heterocyclic flavor compounds. These ring compounds reflect light in such a way that the food/onion takes on the familiar brown hue we recognize. These transformations also produce a plethora of volatile flavor and aroma compounds, which combine with one another to produce even more nuanced tastes and smells. Ranging from malty to greasy, they depend on the exact composition of sugars and amino acids in the food. The Maillard process accelerates in an alkaline environment. You can see an infographic of the Maillard reaction here.

Unlike the Maillard reaction, caramelization is exclusively the breakdown of sugar molecules under high heat. Sugars decomposes into glucose and fructose and eventually the individual sugars undergo dehydration to form new flavor compoounds that taste of caramel. Some of these compounds have been identified as diacetyl (butterscorth), esters and lactones (alocholic), furans (nutty) and maltol (toasty). The ratio of the Maillard reaction to caramelization that occurs on a piece of food depends on its protein and carbohydrate content.

Onions have sugar content ranging from 5% (storage onions) to 15% (sweet onions) and 8% protein (surprising!). As they are heated the Malliard reaction and caramelization occurs, the strong pungent sulphur compounds breakdown, new sweeter flavour compounds develop and replace the bitterness. The Malliard reaction is said to proceeed from a lower temperature limit of room temperature, whereas caramelization only takes place above 120-150 degrees Celsius.

Methods tested

Caramelized onions by dehydration, slow cooker and stovetop. As a control I will use large red onions, the most common in the supermarket. Red onions are milder than yellow onions but since I had a bag of red onions I used them. This BuzzFeed article nicely summarizes the uses and tastes of different onion varieties. Recipes for the individual methods may be found at the end of the post.


Slow Cooker / Crock pot

The slow-cooker onions came out more stewed instead of caramelized. The rings remained fairly plump and retained a juicy bite, but were lacking in depth of flavor, perhaps diluted by the excess moisture and limited evaporation.

Stove Top

Cooked over one hour over low heat in a non-stick pan, two cups of onions whittled down to an infinitesimal amount. How much those cells have shrunk! They were semi-crispy with and boasted a butterscoth sweetness so incredible you’ll find it hard to believe those mahogany worms are composed of but onions and olive oil. I did add a pinch of baking soda to alkalize the conditions to speed up the process because at the 30 minute mark, things were going nowhere.

So good with balsamic vinegar. I ate all in one serving (read: two whole onions originally). Excuse the onion breath.


I decided to decompose this project into a further experiment, testing if red or yellow onions made a difference. On the left is yellow onions coated in date-tamari paste, and red onions on the right as a control. It did not make a noticeable difference in taste, although the yellow onions were somewheat meatier and did not shrink as much as the red.

As mentioned in the introduction, the Maillard reaction is sped up at warm temperatures and caramelization occurs only above 120 degrees Celsius. Since in the raw version the onions are dehydrated on low heat not above 48 degrees Celsius, date paste and tamari are used as seasoning to give the caramelized effect. But not to worry, inauthentic as it sounds, the seasoning does not detract from the onion. After 10 hours in the oven/dehydrator, the final product resembled chewy onion leather with the flavors of both the onions and seasoning paste intensified into a delicious lattice mess. I used a regular oven; ideally the texture is supposed to be crispy if made in a dehydrator. On hindsight, Using maple syrup instead of date pasta might have been a better choice as sweetener instead of dates as dates result in generally stickier products.


For meaty juicy onions and occasions when you are strapped for time, slow cooker is recommended.

For true caramelized onions with an intense sweetness, the classic stove top works best. You also have more control over the level of doneness, caramelization and crispy factor.

If you are intending to keep your onions “raw” and/or crispy (ideally), use the dehydator method. It is also great if you are strapped for time.

Enjoy them onions in salads, with cheese or with your favorite vegetable burger. You wouldn’t want to miss my devine raw and vegan French Onion Soup, coming up next!


Caramelized Onions Three Ways
Three methods to enjoy caramelized onions, with different textures and time demands to suit your needs.
Recipe type: Condiments
Serves: ½-1 cup onions for each method
Slow cooker caramelized onions
  • 2 medium red or yellow onions, French cut into ¼-inch (6 mm) slices
  • 2 teaspoons extra virgin olive oil
  • 1 teaspoon balsamic vinegar
Stove top caramelized onions
  • 2 medium red or yellow onions, French cut into ¼-inch (6 mm) slices
  • 2 teaspoons extra virgin olive oil
  • ⅛ teaspoon baking soda (optional)
  • 1 teaspoon balsamic vinegar (optional but highly recommended)
Dehydrator caramelized onions
  • 2 medium red or yellow onions, French cut into ¼-inch (6 mm) slices
  • ¼ cup date paste (from 8 Medjool dates, see Notes)
  • 4 teaspoons tamari
  • 2 teaspoons extra virgin olive oil
For slow cooker method
  1. Place the sliced onions and oil in the slow cooker. Toss well so that the onion slices are well coated with oil. Cook on high for 6 hours, checking periodically to ensure the onions are not burnt. You may also cook on high for 2 hours, then change the setting to low for 4 hours, and finish up on high again for another 1 hour or so. The final texture should be soft and juicy.
  2. Remove onions from pot and mix in balsamic vinegar if desired.
  3. Store refrigerated for several days in an air-tight container.
For the stove top method
  1. Heat a large non-stick skillet over low heat. Place the sliced onions and oil in the skillet. Toss well so that the onion slices are well coated with oil. Spread the onions out evenly over the pan and let cook for 40 minutes to an hour or more, stirring every few minutes.
  2. As soon as the onions start sticking to the pan, let them stick a little and brown, but then stir them before they burn. Continue to cook and stir until the onions are a rich, brown mahogany color. If the carmelization process is too slow, you may speed it up by adding a pinch of baking soda.
  3. Remove onions from pan and mix in balsamic vinegar if desired.
  4. Store refrigerated for several days in an air-tight container.
Dehydrator method
  1. In a small bowl, make the seasoning paste of date paste, tamari and oil. Coat onions very well with the seasoning paste. Spread on dehydrator sheets or a parchment-lined baking tray and dehydrate until crispy. For oven method, dehydrate on the lowest setting for 6-8 hours.
  2. Remove onions and mix in balsamic vinegar if desired.
  3. Store refrigerated for several days in an air-tight container.
It is recommended to add salt while caramelizing to draw out the moisture. I omitted this time but had I known, I would have added a pinch.

To make date paste, soak dates in water for 20 minutes to soften. Remove skin and pits, then blend in a food processor or for small quantities, grind into a smooth paste with a mortar and pestle. Add reserve date water as necessary.


Cuisitive: Caramelization.


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