I usually make the French onion soup with white onions. The prodecure I normally use is as followed:

  1. I slowly caramelize them on a low heat for around 40min.
  2. Then I add some sugar, salt and oil before finally adding broth.
  3. I let this come to a boil.

I followed the same procedure with the red onions expecting something sweeter, but the end result was a tasteless soup. Since all the ingredients and steps were the same except for the red onion, why did my French onion soup come out tasteless and bland?

2 Answers 2


Typically you should use yellow onions for cooking. They have a higher sulphur content and are more flavorful after cooking. Raw, a red onion will taste more pungent. However, once cooked it is more mild and sweet than a soup would require. Red, as well as other sweeter onions, have more sugar and water than their yellow counterparts. For more details on the profile, seriouseats has good primur.

If you wish to improve your results, you might slice more thinly and add some salt in advance of sweating (rather than before adding broth) to draw out the excess moisture, as the onion's moisture (more prevalent with red onions) will inhibit browning, ergo inhibiting caramelization and the maillard reaction that break the bigger sugars into little ones and lend flavor through browning. The explanation at norecipes also adds that deglazing with sherry can slow down the process if you are experiencing uneven browning. Another possible tactic would be adding a 1/4 teaspoon of baking soda per pound chopped onion; this will speed up browning.

Ultimately, unless the recipe calls for red onions, you are going to get better results with yellow onions in terms of raw, "sweet and tangy" onion-y flavor. You can use the tips above to try to overcome that, but a nice big bag of yellow onions are going to do you better in the long run, and if you put the same effort into the it will take less time, taste better and be less expensive.

  • great answer, thanks. Red onions on burgers taste great with perfect taste compared to yellow ones, and I wanted that taste, but maybe in a soup it does not work out. Could it have been because I had put a bit of water in the first stage of boiling??
    – Vass
    Commented Mar 9, 2012 at 18:52
  • The water would delay the process minimially, it's really just the onions. Red onions are best raw or grilled. A bunch of water would start a sweat, and delay until the water evaporated. Caramelizing onions is slow and tedious and a labor of love
    – mfg
    Commented Mar 9, 2012 at 18:53
  • so the boiling prior to frying until max caramalization did not do it. Could having used butter instead of olive oil been responsible?
    – Vass
    Commented Mar 9, 2012 at 21:54
  • 1
    @Vass To be clear, I wasn't recommending using a bunch of water in the beginning, or any actually. The water will ultimately inhibit the reaction. My recommendation is just to use yellow onions. Caramelizing red onions serves no purpose. Here is another question about using water in that way
    – mfg
    Commented Mar 9, 2012 at 22:01
  • 3
    @Vass, using butter instead of olive oil definitely might have adversely affect the carmelization as butter is not 100% fat and contains a significant amount of water. Approximately 16-17% water.
    – Jay
    Commented Mar 21, 2012 at 14:43

One of the things that I noticed when making onion or French onion soup is that you need to use a good amount of onion. Definitely caramelize them. Personally I like to use more than one type of onion as well. Adding leeks and two or more other types of onion make for a nice flavorful soup. Then finally it is important to use a good flavorful stock or broth. So to answer your question it could be one of a few things. Maybe there weren't enough onions, the broth was bland.

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