Does it matter if I sauté onions for high liquid foods

onions

Many (most?) recipes ask that you sauté onions before adding other ingredients when making soups, stews, or other dishes that contain lots of liquid (as opposed to something like a stir fry).

I'm not taking about caramelization — I understand the purpose of that. I mean recipes that ask you to "sweat" the onions or cook them until they're just translucent, with no browning.

Cooking the onions this way makes sense if you want to reduce the moisture and concentrate the flavors. But it seems to me that if you're adding the onions to soup, for example, you're reducing the moisture just to put moisture back in it.

Does it really make a difference in a soup or stew, as opposed to simply adding the raw onion along with other ingredients?

Best Answer

I make soups both ways and there is a clearly different end result. I'm not sure the exact mechanisms going on but I'll list some hypotheses/thoughts:

  • I'm sure if you boil the soup for a very long time any differences will approach imperceptibility, but many soups aren't cooked for a super long time.
  • Anyone who has experimented with this knows that the texture of onions changes much faster when you are sautéing or sweating compared to boiling. Thinly sliced onions will still have some of their firmness even after an hour of a slow simmer.
  • Even on low heat the cooking temperature will be much hotter than simmering water. Although you aren't cooking them long enough for caramelization / obvious Maillard reactions, you will still be introducing some of those flavor compounds into the mix.
  • On the flipside, the heat of the initial sweat will also destroy some compounds present in raw onion, much like how raw garlic is different than sautéed garlic which is different from roasted garlic. Many recipes probably include a sweat purposefully to remove the "bight" you get from raw onion. Of course those flavor compounds may also be desirable for some dishes.
  • Sweating also introduces evaporation, but this probably isn't one of the bigger factors.
  • Finally, a lot of the above arguments also pertains to the oil as well. Olive oil that's been sautéed with something is going to taste differently in the end compared to just throwing it in while the soup is boiling. (As Anastasia Zendaya points out, the flavors of the thing you are sautéing will be added to the oil, but I'm focusing more on how the heat itself is changing the fat you are using).
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