tomato paste for canning

 Today I'm canning tomato paste.  These are all San Marzano tomatoes that I grew in my garden, and as I got overwhelmed with processing them in the summer, I just cleaned them and tossed them into Ziplocs in the freezer.  I pulled out a couple of bags last night and filled the pot and put in the refrigerator to thaw overnight.  Spoiler: they didn't really thaw, but they were thawed enough to be able to chop them.  

I'm using the official recipe from here, with some modifications.  Yield they say is about 4-4.5 half pints (though I'm putting into quarter pints and reusing other small jars). 

Tomato paste recipe

Ingredients

•  7 pounds tomatoes - paste variety
• 1/2 tsp citric acid or ** lemon juice
• 2 bay leaves
• 1/2 tsp salt
• 1 clove garlic

Instructions

• Prepare jars (4-5 half pints worth) and lids; keep warm.
• Clean tomatoes if not already done.  (Recipe calls for coring which I did not do.)
• Chop tomatoes.  I chopped them in half or quarters depending on size (they were small); recipe calls for 1/2-3/4 inch size.
• Bring to a boil, then slowly simmer until volume reduced by half (an hour or more).  Keep stirring regularly to keep from burning or sticking.
• Remove from heat and run through a food mill or a sieve.  (Recipe specifically says not to use food processor or blender but I"m not sure everyone follows that)
• Return to pot, add remaining ingredients.
• Cook slowly until reduced by half again (two or more hours).  Stir frequently and be careful of hot spatter.
• Remove bay leaf and garlic.
• Put into prepared jars, remove air bubbles, 1/2" headspace, clean rims, lid.
• Process for 45 minutes in half pint jars.