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Mar 26, 2011 08:20 AM

Dutch Oven: Onion Caramelizing Problem / Questions / Chemistry

Caramelized onions came out of my Dutch Oven with a bitter, (sulfurous?) taste and I'm wondering why.

The dutch oven is a 6 Quart enameled model. I used about 3 pounds of Oso Sweet onions - generally a very sweet variety.

I followed what has been described as the Cook's Illustrated method: sliced onions placed in oiled DI with butter & salt, then put in 400 degree oven for an hour, stirred, put back in oven with lid ajar another hour, then finished stovetop with a browning deglazing iterations.

When the DI was removed from the 400 degree oven, the onions were greatly reduced in volume, and the top layer of onions were taking on a hint of gold color. But there was a lot of water in the bottom - most of the onions were simmering / steaming. After another hour in the 400 degree oven with the lid ajar there was still a large amount of water. Finishing on the stovetop, it took quite a while at medium heat to dry it out.

The onions had a somewhat acidic bitter taste. I am wondering what went wrong.

Is 400 degrees too high? It seems a bit much for what I think of as low and slow. Certainly this is a lot higher then the crock pots some people use to caramelize onions, and it seems higher then what I have used stovetop in my cast iron skillet for this purpose. I would have guessed a temperature in the range of 250 to 300 might have been better.

Might the onions have been too wet for too long?

Onions with too much acid for good Maillard reaction?

Would plain cast iron be much better for the Maillard chemistry?

Thanks for your thoughts!


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  1. Perhaps it was the variety of onion. Remember CI does not recommend sweet onions for their recipes (especially their onion soup recipe). Thus, there may have been too much sugar that eventually burned and provided the off tastes. Try the recipe with regular onions. Spanish or yellow onions are typically my go to onion.

    1 Reply
    1. re: wanker

      The taste seemed sulfurous or acidic, and was present without any significant darkening or burning. And I thought the sweet onions generally have less acid. Not to say that a yellow onion might not have worked better though...


    2. I'm guessing the acidity of the onions may be the culprit. You can add a pinch of baking soda at the beginning of the process and it might reduce the acidity of the onions. It also helps with the browning process.

      1 Reply
      1. re: madtheswine

        I wouldn't cook using that method again if I were you:

        Here's how I would caramelize onions for onion soup for example.

        !.) I sautee the sliced onions in a Dutch oven OR sautee pan medium heat with lid OFF on the stovetop. We don't want to steam our onions, we want to keep them on the dry side.

        I would use a high heat oil like Canola and stir the onions in it and use medium heat to cook them.

        You steamed/braised yours in the oven making them soggy and then burnt them on the stovetop.

        2.) I would expect the onions to take some time to cook properly, so I would check them often

        and adjust the heat as necessary to keep a balance of dryness to enough oil to keep them from burning. Your bitter / overly sweet taste is because you burnt your onions.

        3) I would give the onion elbow room to brown properly...if they're crowded they steam/braise.

        If it's necessary to achieve space, I cook the onions in batches and set the caramelized ones aside as I cook the next batch.

        4) I would be patient and attentive.