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1
Heat oven to 325 degrees.
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2
Core and halve tomatoes and scoop out seeds and gel.
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3
Pile tomatoes into a large roasting pan, or on 2 sheet pans, cut side up.
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4
Do not add oil.
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5
Roast tomatoes for 2 hours.
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6
Thoroughly puree tomatoes using a blender or immersion blender.
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7
It should be smooth and velvety, with no pieces.
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8
Put a rack in a large stockpot or line pot with a folded kitchen towel, then fill pot with water and bring to a boil.
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9
Add pint jars and boil for 10 minutes.
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10
Jars may be left in warm water until ready to fill.
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11
Alternatively, sterilize jars by running them through a dishwasher cycle, keeping them warm in the machine.
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12
Place canning rings in a small saucepan, cover with water and bring to a boil.
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13
Turn off heat and add flat lids to soften their rubber gaskets.
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14
Rings and lids may be left in water until jars are filled.
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15
In a nonreactive pan, bring puree to a brisk boil for 5 minutes.
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16
Ladle hot tomato puree into warm jars leaving 1/2 inch head space, plus room to accommodate lemon juice.
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17
If using citric acid, fill to 1/2 inch head space.
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18
Into every pint jar, add one tablespoon lemon juice or 1/4 teaspoon citric acid.
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19
If using salt, add 1/2 teaspoon to each pint jar.
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20
Wipe jar rims clean with a damp towel.
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21
Place lids on jars, screw on rings and lower jars upright into boiling water.
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22
Return to a full boil and process for 35 minutes.
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23
Transfer jars to a folded towel and let cool for 12 hours.
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24
Jars will ping as they seal.
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25
Once cool, test seals by removing rings and lifting jars by flat lids.
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26
If a lid releases, the seal has not formed.
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27
Unsealed jars should be refrigerated and used within three days or reprocessed.
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28
Rings and jars may be reused, but a new flat lid must be used each time.
