There are a lot of canned tomato products. I mean, seriously, it's a little silly. Last night, while grocery shopping with my wife, I was asked to retrieve a cans of diced tomatoes, tomato purée, and tomato sauce. While searching through the mulitudes of sizes and flavors, I absent mindedly swapped purée for paste and grabbed the wrong can.
What took me back as I was searching was just how little I understood about canned tomato products and why they exist in such variety. So I decided to do some investigation: what types of canned tomatoes can one find in a typical American grocery store and what are they used for.
Starting from the largest and working our way down, we have whole tomatoes, both peeled and unpeeled. Peeled tomatoes are the most common variant and are made by first briefly boiling them to make the skin looser, removing the skin, and then placing them into a jar or can. While not particularly appetizing by themselves, they're easily turned into other "states" of tomato. Some sources that I have found suggest that canned, whole tomatoes are of a higher quality than other, more processed varieties, with the manufacturers sending dud tomatoes off to be chopped up.
A variant of whole tomatoes, stewed tomatoes have been cooked — boiled longer than a typical whole tomato. This releases the flavor and makes them more suitable for adding to many recipes. Of course, it's easy enough to cook whole tomatoes, especially if the dish you'll be adding them to will be cooking further anyways. It is common to find stewed tomatoes with added ingredients and seasoning.
Diced (or chopped) tomatoes save some of the labor involved with working with whole tomatoes. Fairly self explanatory, they work well in salsas and sauces where you want full pieces of tomato. On the grocery store shelf, I found plain old diced and petite diced, as well as a myriad of flavor additives such as garlic, pepper, and oregano. Hunt's website lists no less than 14 different varieties. Yes, you read than correctly, one-four - fourteen.
Take your canned tomatoes and mash them up. Boom, crushed tomatoes! Typically, crushed tomatoes will be run through a strainer to remove seeds and other large chunks. They're great for sauces and chilis where you're looking and some of the texture of tomatoes without the chunks.
Crushed tomatoes still too chunky for you? Try purée. Take the same, whole tomatoes but blend them instead of just crushing them. You'll still need to strain them to get the seeds and other large chunks out. This is what foods like pizza sauce and ketchup start as.
So far as I can tell, tomato sauce is to tomato purée as stewed tomatoes are to whole tomatoes. It's been both liquified and then cooked. It will often have seasonings added to it as well. This is different than your typical "pasta" sauces, mind you, which almost certainly have added seasonings and non-tomato ingredients and may include chunks of tomatoes.
Tomato paste is the last major variation that canned tomatoes come in (to my knowledge). You take the tomato purée or sauce from the prior categories and then you cook it more. And then you cook it more. And then some more. Tomato paste is effectively highly reduced tomato sauce that has had most of its liquid cooked off. This is used when you want to add tomato flavor to a dish without adding extra liquid to a dish. It can actually help to thicken a dish to a modest degree.
If you've made it this far, you should be pretty amazed at the various phases of matter that tomatoes can exist in. I mean, holy crap, that's a lot of tomato. I don't even like tomato all that much and I am impressed. If you start throwing in all the flavors, extra ingredients, and low-sodium varieties, the multitude of options is staggering.