As you can see from the picture in the last post, I grow a lot of different types of tomatoes, many of which are pretty small. It's obviously not feasible to skin a cherry tomato, so my method works well for a big batch of different sized fruit.
To avoid having your finished tomato sauce separate, you need to minimise the time between breaking the tomato up and getting the sauce boiling. This is because there is an enzyme in tomatoes (the snappily-named polygalacturonase) which will degrade the natural pectin in the tomato once it is exposed to the air and will turn the fruit and the resulting sauce runny. You want to get the tomatoes onto the heat pronto to stop the polygalacturonase breaking down the pectin.
My method is to quickly process the fruit in batches of about two pounds at a time and to liquidise the tomatoes in a food processor before putting them through a food mill.
If the tomatoes are large, I cut out any hard white parts and chop them into halves or quarters. With the smaller tomatoes, I just remove the stalks and put them whole into the food processor. The picture above shows what was left after I'd done that to ten pounds of tomatoes: not a lot, really.
After 20 seconds of processing, the tomatoes are a runny sauce, which I then put straight through the food mill set over a large pan which is already on a medium heat. It only takes another 20 seconds to pass the liquidised tomatoes through the mill, which takes out the skin and most of the seeds. My mill is just the right size to hold the two-pound batch of sauce.
This picture shows the leftover seeds and skin, which go into the compost bin. Big tomatoes have a lot more flesh in proportion to the seeds than small ones.
Once the first batch of sauce is bubbling away, you can trim, process and mill the next two pounds, and so on, until you've done five batches and the pan is nearly full. I estimate this ten pounds took about twenty minutes to get to this point (well, not counting the picking part. Or the seeding/planting/growing/staking parts...).
The next stage is easy - you just leave the pan on a medium heat for about two hours, or until the sauce is at the consistency you want. I cook mine until it's about half the original volume. And it's always a good idea to set a kitchen timer, because it's easy to forget about it. I give mine a stir about every half-hour.
The reduced sauce:
Up until this year, I always froze the batches of sauce in medium-sized freezer bags. But with an investment a few months ago in a pressure canner, I now use that to further process it. I add a little lemon juice to the jars to make sure that the sauce is acidic enough to be canned. It takes 20 minutes at high pressure to make the jars safe to store in a cool, dark place.