Step by Step Instructions for Canning Oven-Roasted Tomato Sauce

Note: Each quart jar is about 2 lbs of oven roasted and boiled tomatoes (about 4-4.5 pounds raw). I try to process about 50 pounds raw at a time, which usually yields me about 25 or so roasted, drained and skinned tomatoes. (Processing 25 pounds at a time would be a great amount to start with for pint jars; it should yield close to a dozen pints.)

Preheat oven to 375 convection roast or 325 bake to oven roast tomatoes. Full directions can be found here.

Cut ends off tomatoes and slice in half lengthwise.

Let cool and slip skins off. Leave seeds.

Lift off parchment, removing skins, and place into a blender (we prefer a vitamix). Blend until smooth – or until your desired texture.

Transfer to large stainless steel stockpot and bring to a boil. I usually boil for about 30-40 minutes. This process will thicken your sauce slightly. If you want your sauce thin, you can simply bring to a boil for 10 minutes and then skip down to hot packing the jars.

Meanwhile, wash your jars and lids and rings. It’s important to even wash your new lids, too. We prefer the brand name lids (Ball and Kerr).

Racks are essential and you can either use one that is divided for quarts (fits 7 total) (below) or one that has no dividers, which is what I use when processing pints jars or smaller as it can fit more jars and has more flexibility. If you were to only invest in one, I’d recommend the flat-bottomed rack.

For all canning, I fill the the pot to this line. With quarts, I will have to remove some water as I fill the canner with my full quart jars. (See below)

Place your clean jars into the canning pot and warm the water to a simmer (no need to boil as the processing of the tomatoes will sterilize the jars). You’ll need to dunk a few in to allow them to sink. Place all the clean lids and rings into a clean bowl adjacent to the canner. (I find conflicting information about whether or not to keep these in a warm water, but I no longer do, again because of the processing time/sterilization.)

When the sauce is reduced a bit and the jars are warm and prepped, set up an area adjacent to your canner where you can lift a jar out, fill it, and return it to the canner one by one.

For each quart: add 1/2 tsp citric acid or (2 Tablespoons bottled lemon juice) to each warm quart jar before you fill with tomato sauce. (1/4 tsp citric acid or 1 T lemon juice for pints)

Using a funnel, carefully ladle your hot sauce into the hot jar. (This is called hot packing.) I fill to just above the lip of the threads where the jar narrows, a generous 1/2” of headspace, which is the recommended height. Overfilling will impede proper sealing.

Run a plastic knife or canning bubbler around the filled jar to remove any air pockets and adjust headspace as needed. I usually find a few bubbles but it rarely causes a dramatic drop in my overall volume.

Our bubbler has a graduated measuring tool on one side that you can check your fill after removing air pockets. Once you can a few times, you’ll get pretty confident in your fill height but it’s a good idea to double check yourself seasonally.

Using a damp cloth or paper towel, clean the rim of the jar off so it’s free of all debris that would prevent proper sealing.

Center the clean lid on the jar and finally hand tighten the ring.

I’m gonna be honest, the lid tends to move a bit as I work to get the ring threaded, but it always works out in the end.

Using the canning tongs, gently lower the jar into the hot water bath.

Once you start filling the canning pot with filled jars, you’ll need to dump 2 or more quarts of boiling water out into the sink to prevent the canner from overflowing. I start this process about halfway through hot packing the jars.

Repeat process as needed.

When the final jar is filled and in the hot water bath, be sure the hot water bath covers at least 1” above the top of the jars.

Bring the pot to a full boil and start your timer for 40 minutes (adjusting for latitude as needed). Lower to a gentle boil, medium or medium low depending on the burner. You need to maintain a boil for the duration of the 40 minutes. I leave the lid slightly cracked too otherwise it sputters the entire time!

When the boil is complete, shut off burner and let sit for 5 minutes before removing jars.

Place jars on a smooth towel and let sit for 12-24 hours before removing lids, checking seals, and moving to their storage location.