I have a soup recipe that calls for 24 oz. dried tomatoes in oil, drained and patted dry. I would like to use dried tomatoes (not in oil), but don’t have a clue how much to use.
Is there a conversion by weight? Should I substitute by volume?
I would probably substitute roughly by volume. 24 ounces in oil looks to be 2-3 cups, based on my memory of jars I've bought and a quick Google image search to confirm.
But I wouldn't do that with them fully dried - I'd rehydrate them in water or stock (the ones in oil tend to be less thoroughly dried out), and then cram them into your measuring cup (because they're certainly crammed into the jars with oil) and aim for 2-3 cups.
I might also add a tablespoon or two of olive oil to the soup to compensate for what's inevitably in the tomatoes even if patted dry.
I tried to find a good conversion by weight based on nutrition facts (usually works!) but unfortunately sun-dried tomatoes in oil are sold by weight including the oil, but the USDA nutrition facts are for drained tomatoes. For what it's worth, based on a label from a specific brand (found a photo here), the ones in oil are 6/19 carbohydrates by weight (and does seem to be including the oil - it says they're also 5/19 fat), while the USDA says dried without oil are 55.76/100. The carbohydrates are all from the tomatoes, not the oil or any additional water, so that should indicate how much tomato there is.
So: 24 ounces * (6/19) / (55.76/100) = 13.6 ounces. But I'm not terribly confident about that estimate, because it's based on so little evidence, and there's a lot of room for variation here. It's at least in the right ballpark, though - I have about 6 oz of dried tomatoes that look to be about 1.5 cups, depending on how packed they are.
Since your recipe calls for 24 ounces, I would expect that to be by weight, not volume. You could therefore simply use 24 ounces of the plain dried tomatoes.
The one caveat to that is if the recipe meant "24 ounces of tomatoes and the oil they were stored in, without the oil" instead of "24 ounces of tomatoes that have been removed from the oil in which they were stored." If the recipe intends the latter, then you can simply do the above no problem.
If however it meant the former, then you have a couple of options. You can either estimate the amount of oil that would be in the jar (for a 24 ounce jar I would estimate ~4-8 ounces, depending on how tightly packed the tomatoes were) and subtract that from the amount of tomatoes you use, or simply use the full amount and have slightly more tomatoes than called for.
If it were me I would just use the full 24 ounces-- soups are very forgiving.
Try to rehydrate before cooking and then use the same amount as in the recipe.
You can adjust the other ingredients afterwards.
(I do assume you will unlikely rehydrate 10 x the amount required).
This is because oil and water densities are not too dissimilar. Moreover the tomatoes called for by the recipe could have been rehydrated, which is a possibility when preparing tomatoes in oil vase.