(Why) do onions taste sweeter when cooked at lower temperature?
I use onions to add a sweeter taste to some dishes, for example in tomato sauce for pasta. I cook them in oil, with some salt, before adding the other ingredients. It seems to me that when I turn the temperature too hot, the onions don't become sweet at all, but rather retain some of their spiciness. They also look less "glassy". Why is this?
Best Answer
Well, you're definitely right. Onions cooked at a high temperature act differently than ones cooked at a low temperature, per "the bible" aka On Food and Cooking. However, it doesn't go in to much of an explanation as to why. Probably the most relevant aspects of what is in there are:
When onions and their relatives are heated, the various sulfur compounds react with each other and with other substances to produce a range of characteristic flavor molecules. The cooking method, temperature and medium strongly affect the flavor balance. Baking, drying, and microwaving tend to generate trisulfides, the characteristic notes of overcooked cabbage. Cooking at high temperatures in fat produces more volatiles and a stronger flavor than do other techniques. (p.311)
Since a low temperature produces less volatiles, I assume that the natural sugars of the onion shine through instead.
It's probably also important to understand where the oniony flavor comes from. The spice, as you describe it, is the onions natural defense mechanism. However, it doesn't exist defacto in the onion, but is rather the result of a chemical reaction. The onion stores very reactive sulfur in the cell fluid, and a seperate trigger mechanism in a storage vacuole. When you cut / crush / cook/ peel the onion, you break the vacuole and the enzyme and sulfur cause a chemical reaction giving off the spice. (p272 & 310)
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Quick Answer about "(Why) do onions taste sweeter when cooked at lower temperature?"
This reaction of breaking down larger sugars into single sugar molecules is what causes sautéed or caramelized onions to brown and develop a sweeter flavor. Heat causes the sugar molecules that make up polysaccharides (at top) to separate into monosaccharides (at bottom) in a process called pyrolysis.Why do onions turn sweet when cooked?
When onions caramelize, one of the main things that happens is the sucrose, or natural sugar hidden within their cells, is transformed into other, simpler forms of sugar, including glucose and fructose. Those sugars taste sweeter than sucrose, which accounts for the increase in sweetness as the onions caramelize.What happens when you cook down onions?
Onions are naturally sweet; and as caramel comes from the simple cooking of sugar when you slowly cook onions over an extended period of time, the natural sugars in the onions caramelize, making the result intensely and wonderfully flavorful.How do you take the sweetness out of onions?
You can remove some of their astringent flavor by soaking them in cold water before adding them to the dish. Quick Cooking Over High Heat \u2013 A minute or two over high heat is just enough time to take the edge off the oniony flavor, but leaves the texture nicely crisp.Why do onions go sweet?
The main reason sweet onions taste so much sweeter than other onions is that they are low in sulfur compounds, especially pyruvic acid, which gives regular, or storage, onions their pungency.Why I cook my onions for 4 hours
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