1) Food preservation makes me happy. I enjoy taking a fresh, raw product and turning it into something beautiful that safely sits on my shelf in glass. It's almost like creating home decor and food at the same time.
2) I can control the quality of the ingredients.
3) Tomatoes canned in tin might leach metal, and most cans are lined with plastic to prevent the leaching. I'm not sure that the plastic is that much healthier than leaching metal! A lot of cans say "BPA free," but I'm just waiting for the other shoe to drop on plastic all the time. I don't think BPA is the only problem.
So, with all those considerations in mind, I got me a 25-pound box of tomatoes from Bulk Natural Foods. I roasted about a third and made salsa, and the rest I processed into tomato paste.
Here's kind of a conceptual framework I work with in making tomato products, by levels of concentration:
1) You can just peel, can, and preserve whole tomatoes.
2) You can cook them down a little and make stewed tomatoes, sauce or puree.
3) You can cook them down further and make tomato butter, ketchup, or add sugar and make tomato jam.
4) You can cook it down even further and make paste.
It's all about how much liquid you're trying to get out of the tomatoes before canning.
So here's what I did.
I slashed the bottom of each tomato, dropped it into boiling water for 2-3 minutes, then removed it into a bowl of icy water. Leave it there for a minute or so.
When they were cool enough to handle, I slipped the peel from each tomato and put it in the compost. I also cut out the cores. Then I sliced them in half through the middle and used my fingers to ream out the seeds and juice. I strained this juice into a jar and saved! Fresh, delicious tomato juice. Yum.
I put the squeezed tomatoes into my crockpot, set to low. I left them there overnight, with the lid slightly vented.
In the morning, they were soft and had released a lot of liquid. Working in batches, I pureed them in my blender. An immersion blender would have been ideal for this, but I don't own one!
After running through the blender, back into the crockpot the tomato puree goes. I left the lid off for about 8 hours that day, and here's what it looked like:
Wow! Big difference, huh? It's cooked down to almost 1/8th of its original volume. You can tell you're getting close when it turns brick red and gets very thick. So thick it won't even pour off a spoon. I added about a teaspoon each of sucanat and sea salt at this point, but that's strictly optional.
Then I sterilized some 4-oz jars in boiling water, filled with the hot tomato paste, wiped and lidded, and processed for 30 minutes in the water. Voila! Tomato paste. 25 pounds of these tomatoes yielded 32 oz of tomato paste, but your mileage will vary based on what kind of tomatoes you have and how juicy they are.