Diced tomatoes promise neatness and convenience: There are no juice-filled water balloons to crush or snip or coax into softness, slowly and patiently, on the stove.
But here's an ironic surprise: Diced tomatoes—which you'd expect to break down much faster (since, duh, they're smaller)—are actually packaged to keep their shape. Those diced tomatoes you bought to save time are making achieving a smooth, homogenous sauce harder (and slower). Those liars.
Food science expert (and whole canned tomato evangelist) J. Kenji López-Alt doesn't call for diced canned tomatoes in his book The Food Lab because...
Calcium chloride is a common food additive used to keep canned fruits and vegetables firm; to coagulate soybean curds into tofu; and to ensure crisp pickles without the hassle of a lime-water soak (lime being another source of calcium). In the case of diced tomatoes, the addition of calcium chloride means they'll retain their bite and shape even as they're cooked.
So, the rule of thumb
If you do find canned diced or chopped tomatoes (like Pomì) that don't list calcium chloride as an ingredient, however, you can use them as you would their whole brethren without worrying that they'll retain their cube-like shape no matter how long they're simmered.
As for avoiding the mess of crushing tomatoes (which, if you're wearing an apron, can be a satisfying tactile experience), we've got some recommendations below; Kenji pokes a hole in every tomato before he squeezes out to direct the spray of juice.
a fresh tomato post-script
While canned tomatoes sure are handy—and we on the East Coast are pulling our reserves from pantries (and bookshelves and bedroom closets)—, let me offer just a brief reminder of the fresh (!) summer tomatoes we can look forward to...
How's that for a little sunshine in the middle of February?
When do you used canned diced tomatoes versus whole or crushed? Tell us in the comments below.