If a recipe calls for canned diced tomatoes and all you have are canned whole tomatoes, can you dice up the whole tomatoes and use those?
We made batches of soup and macaroni and cheese following recipes that call for tomatoes. We found that the canned diced tomatoes were firmer than whole peeled tomatoes cut to resemble diced. But while the differences were detectable, we decided that in cooked preparations in which intact pieces of tomato aren’t the focus, cut-up whole peeled tomatoes work perfectly well in place of canned diced. When used raw, however, hand-chopped canned whole peeled tomatoes did not perform as well. In salsa, tasters found the diced tomatoes pleasantly resilient, while the chopped whole tomatoes were “squishy” and “limp.” Likewise, in our Maque Choux (see related content), a stewed corn-and-tomato dish, diced tomatoes kept their shape, while chopped whole tomatoes stewed into a pulpy puree.
Why are diced tomatoes firmer and more durable? The juice in which diced tomatoes are packed is treated with calcium chloride, which fortifies the cell walls and helps the tomatoes hold their shape. Many whole tomato products are also packed in calcium chloride–laced juice, but the solution acts only near the surface of the whole tomatoes, leaving the interior fragile.
THE BOTTOM LINE: Hand-cut canned whole peeled tomatoes will stand in for diced when you don’t need the diced to hold their shape. When distinct chunks are important, stick with canned diced.