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I want to make a tomato soup, but my girlfriend tells me that, from the tomato we have, the soup will be too watery. Now I've read that one could use tomato paste/puree as a thickener, and still keep a rich tomato flavour. But what would be the right dosage of paste? Is there any other advice/method to make a good tomato soup from my watery tomatoes?

UPDATE: Thanks for all your answers, unfortunately the most accepted answer seems to be quite time consuming, and I won't have that much time before tomorrow, the big day. It's my fault really, as I should have told that I had some time constraint. However, I want to try @Michael's solution another time, as it seems really interesting. In any event, I'll give a further update the day after tomorrow.

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I always start my tomato soup with a roux anyway... If you don't mind the flavor, this will certainly thicken nicely. – Shog9 Dec 15 '10 at 16:09
up vote 4 down vote accepted

You can add quite a lot of tomato paste/puree but this will mask the fresh flavour of your tomatoes.

I think I'd just reduce the soup down once it was made or add carrots. Carrot flavour really complements tomato soup and many tomato soups recipes require carrots. The starch will then help you thicken the soup.

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Be warned, carrots will noticeably sweeten the soup. Fine if you like that, but... – Shog9 Dec 15 '10 at 15:42
@Knives, @vwiggins: The recept needs 800g of Tomatoes, and I have 2 cooked potatoes at my disposal (so maybe it would compensate for the sweetening effect of the carrots). To my knowledge, no thickener is used in the recept, as the intent was to use ripe tomatoes with a lot of meat. (But I'll have to use the tomatoes we have, otherwise it will be a waste) Which quantity of tomatoes should I replace with carrots/potatoes? – Eldros Dec 16 '10 at 8:50
Sweetening the soup was just what I needed! – Eldros Dec 19 '10 at 6:57

One thing you can do is dry off much of the water by slow-roasting the tomatoes in the oven first, similar to what I do in this risotto. I think you will get a more complex flavor than if you boil the heck out of them in a pot to reduce. I was also going to suggest pureeing them and then hanging them in a cheesecloth bag to drain the water, but you'll lose too much flavor that way.

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It seems like I will have time, so I would like to have some clarifications: As I want to make a soup from the tomatoes, do I need to let the tomatoes in the oven, as long as for your risotto? – Eldros Dec 17 '10 at 12:39
@Eldros: I've done quite well roasting tomatoes at 350°F for around an hour (maybe up to an hour and a half). This gets you plenty of good flavor, and takes out a lot of water - sometimes I end up adding liquid back in to make soup or sauce. You could check in on them now and then and stop when they've lost enough water for you, though you'll lose some of that roasted flavor, of course. – Jefromi Dec 17 '10 at 18:21
I didn't use your method, so yours is not accepted answer, but you deserve at least a +1 for the innovative way. If I have the occasion I'll have to try eat and see if it makes a difference. – Eldros Dec 19 '10 at 6:56
Your second suggestion would work if you collected the liquid and boiled it down, adding it back to the tomato solids after it was sufficiently reduced. – Callithumpian Jun 4 '12 at 4:35

One trick I use for thickening soups is instant mashed potatoes from a box (we also freeze leftover real mash for soups, but it doesn't work quite the same way). I would think you'd want to be careful about using too much in a tomato soup, but it might be worth considering if your soup only needs a little help.

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Instant mashed potatoes taste like nothing except cardboard from the box to me... – justkt Dec 15 '10 at 15:36
@justkt: That's why we use them for thickening soups. They are a fairly pure starch that doesn't add much flavor, and yet doesn't seize in the way that flour or cornstarch/tapioca starch can. Instant mash served as actual mashed potatoes is an abomination and should be avoided at all costs. But it works well as a mild thickener. – bikeboy389 Dec 15 '10 at 15:39
I have heard this is quite effective, good answer! – Jenn Dec 16 '10 at 16:09

Add potatos! You generally won't taste them but they'll add thickness to your soup.

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It might be too late to help you, but for others -- consider not using the whole tomato.

Rather than using whole tomatoes, if you slice them in half (through the equator, not along the stem/blossom line), and then take out the gel in the seed cavities, you'll have almost all 'tomato flesh'. I just use a clean finger (shove it in the cavity to loosen the seeds, then a flick of the wrist over a garbage can to extract any bits still left).

If you're going to be peeling the tomatoes, too, peel first, then take the seeds & gel out, but it's going to get messy (and I'd work over a garbage bowl, not the garbage can directly, as they're going to be slippery). Of course, if you use Michael's recommendation, you don't have to separately peel the tomatoes, as the skin will come off easily after roasting)

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I do this when I want to remove water, but Cook's Illustrated has noted that most of the flavor is in the gel. Still, it's useful at times. Another way to remove the gel and seeds is to whirl tomato slices in a salad spinner. – justkt Dec 17 '10 at 17:45
I understand some people don't care for the added bitterness of seeds, but not using the whole tomato would feel like an immense waste to me. – zanlok Dec 17 '10 at 21:23

Corn starch shouldn't effect the flavor much. Or try wheat flour which is usually handy, though that does have the more "bready" taste. This is basically the same as the roux comment. For variety and less flavor impact try rice flour or starch.

If you've already got it mostly done and you're on a tight schedule, adding one or both of those will thicken any soup/sauce after simmering for another 2 minutes. I must have rescued a hundred dishes this way.. sauce mostly, but also an occasional stew, chili, or soup.

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I made a tomato broth as the recipe called for and loved the taste, but it was thin as broth should be and I just wanted something thicker with more body. So I added a 6 oz can of tomato paste, 1/2 cup of cream and another pinch of salt and white pepper to the 2 1/2 cups of tomato broth I had already made. It worked out perfectly! it was thick and creamy just as I had wanted with great tomato flavor.

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