The first thing you will need is about 50+ Roma tomatoes.
So I forgot to take a picture of this process with my camera, did with my cell phone....but I can't figure out how to get those on here easily. But you put the tomatoes through a food mill, it separates the seeds and skin and leaves you with the meat of the tomato and all its juices. It looks like the picture below.
I filled this pot full and a 2.25 quart pitcher full of the tomato juice and tomato meat.
I used a ladle and scooped out the mixture and put it into the pitcher and then poured it through cheese cloth and a strainer, this helps get rid of all the extra water. If you don't it would take hours to cook off all the extra water. Even doing it this way took a lot of time, if I had a larger strainer I could have done more at one time.
This is what my oven looked like for a whole day, it was hot in the kitchen.
So I used the crock pot on high and it still took hours to cook off the extra water that was left over and to make it thicker.
Once it is thick enough, something about putting it on a spoon and it holding its own, I couldn't wait much longer, it was already 7pm and I still had not put them in the jars yet. (why do they call it canning when you use jars?)
Again forgot to take a picture of my homemade funnel, it was a sports bottle cut in half so it wouldn't spill everywhere. I had the jars in the dishwasher because they were all nice and clean and sanitized, you boil the lids and rims to sanitize as well. Just leave them in there and take out as needed, keeping the water hot. Make sure the rim of the jar is nice and clean, no tomato paste on the rim of the jar.
Pack the jars leaving 1/4 inch at the top and add 2 tablespoons of lemon juice to help it not to spoil.
Make sure you have enough water to cover the jars with 1 inch of water in the pot. Boil for 45 minutes, keep a tea pot full of hot boiling water to add to the pot as the water boils off.
Take out and let cool over night, you should hear the lids pop and that is a good sign, that means that it sealed. If the lid can push down and it pops back up then it didn't seal and you should either put it in the fridge to use within 2 days or throw out and start all over again. Thank goodness that all mine sealed. I also canned the left over tomato juice...why not, can be added to soups, sauces when ever water is called for...you could also drink it.
I got 8 jars of tomato paste
and 12 jars of tomato juice. I think next year I might just roast the tomato paste and freeze it, then use the jars and can something else.