Look for paste tomatoes; it’s important that you find tomatoes as meaty as possible. Wash the tomatoes to get dirt and debris off the outside, and checking each one for blemishes or moldy spots. Soft or split tomatoes are fine to use, but cut out any black or spoiled spots. Cut the tomatoes lengthwise in quarters, as they’ll fit through the strainer better.
Follow the directions for your specific strainer. You’ll want the squeezings (the remains) to be as dry as possible. I put them back through the strainer once or even twice, to extract the most pulp that I possibly can.
Put all the tomato pulp with the onions and garlic in a wide pot, and begin cooking it. Bring it to a full boil, and then reduce the heat to a simmer, stirring occasionally, until the sauce is reduced by at least half. This can take hours, depending on the size of your pot. A wide pan is much much better for this – greater surface area will reduce the sauce more quickly. You’ll get better flavor from a slow simmer than from a violent boil.
We sometimes cook the tomatoes outside, only using the stove in the kitchen to seal the jars. We use a Browning stove with 2 30,000 BTU burners, and were able to keep two big 20-quart pots bubbling at once. It kept the mess (wash, cut, squish, AND cook) in one place, where the crew could switch jobs, chat, share jokes and stories, and laugh at the confused squirrels who hoped for handouts.
CANNING IN BOILING WATERBATH
As always, have your jars clean and hot. If you’re going to put hot sauce in jars, then the jars in hot water, you need hot jars! Thermal shock can crack glass, and your work is wasted. Pour hot water over lids, do not boil them. Add salt and citric acid to each jar.
Ladle the sauce into the prepared jars, leaving ½ inch headspace. Release any air bubbles trapped by sauce. Wipe rims clean, cap and screw on jar bands. Process in a boiling water bath: 35 minutes for PINT jars, and 45 minutes for QUART jars.
When the time is up, turn off the heat, remove the canner lid, and let the jars rest, still in the water, for 5 minutes. Remove jars, place on a towel-lined counter, and set them aside for 24 hours. After that time, remove the bands, check the seals, label, and store the jars in a cool dark place for up to a year.
ABOUT SAFE CANNING
It’s critically important to balance the quantity of low-acid vegetables with added acid, in this case powdered citric acid, which is easily available where you can buy canning jars and other equipment. The tomato sauce must be acidic enough to be safely processed in a boiling-water canning method. Do not increase the onions and garlic; do not add other vegetables; do not add oil.
Tomatoes may be pressure canned. Process pint jars AND quart jars at 10 lbs pressure for 15 minutes.
It is NOT recommended to use a steam canner. They do not have the capacity to generate steam for the long processing time required.