I haven't tried the tomato soup yet, but if it makes you feel any better, I am always a bit over on my yields on anything I have to boil down. Usually only by a pint, but always over. I think it is because I am always worried about boiling down too far and making it too thick so I take it off too early. I have actually considered etching into my most commonly used stainless steel pot where my levels are because their descriptions of things "piling up on spoons" mean absolutely nothing to me ;)

A yield that far off, that different, often indicates an issue of some kind. +/- 1 jar is common but 2x as much isn't common. It could be something as simple as mis-measuring or not cooking down enough.

I'm not saying it isn't safe just that the results shouldn't normally be so far off. So in the future rather than sticking with the 15 min. cooking time (which is just an approx.) try cooking it longer to a thicker texture. It can always be diluted a bit after opening if necessary.

Dave

Dave, maybe it's just me but that makes very little sense. You cook the soup to evaporate the moisture, then open the jar and just add it back in? Why not just leave it there in the first place and save time and electricity?

I do agree that having twice as much product is unusual and I'd look carefully at my methods and ingredients, but I wouldn't cook it longer if the texture was acceptable to me.

Annie

I agree that when the yield is so far off it's a concern. I was wondering if it was a typo, actually. With a new recipe I'm always going back to the book so I'm pretty sure I measured correctly (although I greatly prefer it when preserving recipes measure in weight instead of cups or quarts...5 lbs of tomatoes seems clearer than, say, 5 quarts or whatever).
The other thing that made me curious is the recipes instruction to simmer until the vegetables are soft, and then run it through a blender or food mill. I ran it through the blender. If I'd used my food mill a lot more fiber would have come out, and that would really reduce the volume. So maybe that's the difference? Or perhaps my "simmer until soft" was not as long as the recipe's, and less liquid evaporated?
If I think I'll have enough tomatoes I may try it again just to see what happens.

Dave, maybe it's just me but that makes very little sense. You cook the soup to evaporate the moisture, then open the jar and just add it back in? Why not just leave it there in the first place and save time and electricity?

Just that the recipe might intend for it to be more concentrated, more like canned condensed soup, so further cooking is an option if that is what one wants. And as we know from other 'cooking down recipes' the time called for in the recipe is often not enough.

Dave