Why did my tomato soup turn thick and brownish?

Question

I tried to improvise a tomato soup following these steps:

• Slice tomatoes, briefly stir-fry for aroma, together with some onions, garlic pepper, salt, and a bit of sugar.
• While still hot, purée all together into the blender.

The result was quite bad: the soup thickened (a bit like jelly) and turned red-brown, rather than fresh red.

Questions:

• Do tomatoes have to be skinned for a reason? Does the skin contain all the starch/jelly-ish stuff?
• What went wrong with the color? Do you have any advice to keep it truly fresh red?
• The above combination with garlic, onions, spices can't be all wrong, can it?

Answer

One of the first things I learned in Indian cooking is that the combination of tomatoes, onions and ginger is self-thickening. As time went by, I realised that the thickening effect is far more noticable with old varieties of tomatoes - "beef" tomatoes and a lot of the modern varieties are difficult to thicken unless partially fried first.

Despite the absence of ginger, I suspect that the thickening is purely a natural action between the tomatoes and the onion, and that the tomatoes used were some particularly nice old variety.

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