08 Sep 2015 • • by Heather Lou

Tutorial: A Guide to Canning Tomatoes

Canning tomatoes tutorial // Closet Core Patterns

I don't think this blog is at risk from shifting over to general "lifestyle" anytime soon, but I do enjoy sharing non-sewing related tutorials every once and a while, especially because I think a lot of crafty people are crafty outside the sewing studio, too. If you're making your own clothes, chances are the DIY inclination seeps into other areas of your life as well.

Every summer around this time of year, I dedicate a day in the kitchen to canning tomatoes. I've been doing this since I was a child, and the labour and results serve not just a practical purpose, but a nostalgic one as well. I learned to can with my mother (and she from hers, and on and on down a long line of kitchen-savvy women through history). She would put on Joni Mitchell and we'd spend the day together (in chatty or silent company depending on what level of "Surly Teenager" I was currently operating on), sterilizing jars, blanching and peeling tomatoes, and singing along to A Case of You over the steamy stove.

For the last ten years or so, I've made an effort to fill my own pantry at the end of each season with canned tomatoes, just like my mother did every September. Once you've got the equipment, they are cheaper and healthier to make than the tinned variety at the grocery store, and it is also reassuring and psychologically gratifying to open a cupboard and see row upon row of summer soldiers, waiting to nourish you in the dead of winter when a real tomato is nothing but a memory.

Canned tomatoes recipe // Canning tomatoes tutorial // Closet Core Patterns

Straight talk: canning tomatoes is a lot of work BUT it's not hard or difficult. Prepare to dedicate a long afternoon over steaming pots of water. Wear sneakers since you'll be on your feet. Blare the music you used to sing along to with your mom, or play a long stream of your favourite podcasts. Enjoy the process. It's 200% worth the time and labour, and if you're in the northern hemisphere, you should still have a few weeks of tomato season left.


Canning tools and canning pot // Canning tomatoes tutorial // Closet Core Patterns

  • A canning pot. It must be large enough to completely cover your jars with water once filled. Pots designed for canning include a metal rack for your jars. You can also use a large stockpot, but you'll need a baking rack at the bottom so the jars aren't sitting directly on the heating element. You can easily buy canning pot sets like this one, which include everything you'll need.
  • A wide mouth funnel and special tongs for removing the cans. Canning accessory kits include both if you already have the pot.
  • An additional large pot for blanching the tomatoes.
  • A small pot to sterilize your canning lids.
  • Measuring spoons.
  • Tongs for lifting lids out of the water (canning kits include a small stick with a magnet on the end for just this purpose).
  • A wooden spoon.
  • Lots of dish towels and a clean washcloth.
  • Large bowls for moving tomatoes around.
  • A colander.
  • A slotted spoon or small strainer to remove tomatoes from blanching water.
  • A sharp paring knife for removing the tomato skins.
  • Canning jars. I use a mix of widemouth and regular quart jars. I also make a few pint jars for recipes that don't call for a full quart of tomatoes. You'll need new lids if you're reusing jars. DO NOT reuse metal canning lids as they do not seal properly. Also make sure to throw away and replace any rusty screw rings.
  • Optional: a food mill. If you'd prefer to make sauce, food mills like this one will separate the pulp/juice from the seed and skins. You then cook the sauce down in a big pot before canning it. I prefer to can whole tomatoes and then cook the sauce as I need it, but it can be fun to do both.


How to can tomatoes-3

  • Roma or Italian tomatoes (the long, smaller variety). You may also can regular field tomatoes, but Romas make the best tomato sauce. A bushel makes approximately 15-16 jars of tomatoes (which retails at the Montreal farmer's market for around $22/bushel). I generally buy a bushel and a half; this year I netted 25 quart jars and 4 pint jars. That will probably get me through the winter but I am only cooking for 2 most of the time. If you have a family, I suggest getting two bushels.
  • Kosher or sea salt.
  • Fresh basil.
  • Fresh lemon juice or citric acid. The secret to safely canning is PH level. You need to add something acidic to your tomatoes to help prevent bacteria from developing. I prefer using citric acid since it's easy to throw in and has no taste, but if you can't find it, a big bottle of lemon juice is fine too.


How to sterilize canning jars // Canning tomatoes tutorial // Closet Core Patterns

People are scared of canning because of things like contamination and botulism. I'm here to promise you that if your jars are correctly sterilized, you add a little acid to  your tomatoes, and you process them long enough in the canning bath, you have absolutely nothing to worry about. Those of you lucky enough to have a dishwasher can safely sterilize your jars in it (some even have sterilizing settings). The rest of us must thoroughly wash our jars in hot soapy water. You can sterilize your jars in a big bath of boiling water, but I prefer to throw them in the oven at 225 F for 20 minutes. Once 20 minutes has passed, turn the oven off and leave them in there until you need them.


Washing tomatoes// Canning tomatoes tutorial // Closet Core Patterns

You need to fill up two pots of water: your canning pot and the stockpot you're using to blanch tomatoes. This can take a long time, so get those going now. Make sure you're using pot lids to cut down on the condensation you're about to unleash. Don't fill either to the top - the water level will rise when you add your tomatoes and jars. I always make sure I have a kettle of water waiting to top off the pot if I need to.

As for those tomatoes... a bushel is A LOT of tomatoes. I've found the most efficient way to clean them is to fill up the tub (after thoroughly cleaning it, obviously) and dumping the whole lot in there. I also give the basil a little swish in the water to remove any loose dirt. The tomatoes are coming straight from the field, so letting them soak for a while helps remove the dirt and pesticides. If you have a big double sink, you can probably skip the bathtub step, but you single sinkers will need the one you have free to cool the tomatoes after they've been blanched.

Washing tomatoes// Canning tomatoes tutorial // Closet Core Patterns


Now that the tomatoes are soaking in the tub and the big pots of water are boiling, prepare a nice, organized workstation for assembly. Since you'll be cooling the blanched tomatoes in the sink, I like to set up right next door. Lay down a towel to put your jars on while you're filling them. Wash and de-leaf your basil and put it in a bowl. Have your salt and citric acid or lemon at the ready.

Get a small pot of water boiling, and gently simmer your metal lids for ten minutes or so to sterilize them and soften the rubber seal. Leave simmering while you're working.


Washing tomatoes// Canning tomatoes tutorial // Closet Core Patterns

Fill up a big mixing bowl with fresh tomatoes, making sure to rub off any dirt with your fingers. Drop them in the boiling water (a big slotted spoon will help prevent splashing).

Peeling & blanching tomatoes// Canning tomatoes tutorial // Closet Core Patterns

Leave them in there for 3-5 minutes, or until the skin starts splitting a little. The skin should slide off the tomato quite easily once they've been blanched, but if you overcook them they will be too mushy to work with. Once they're ready, use your slotted spoon to transfer them back in the bowl, and then drop them in a cold sink full of water at your canning station. Work in batches. I find a large mixing bowl of tomatoes makes 4-5 jars at a time so you'll want to blanche at least two rounds  of tomatoes for every group to get in the canning pot.


Canned tomatoes recipe // Canning tomatoes tutorial // Closet Core Patterns

Bring a jar out of the oven or dishwasher and fill each quart jar with:

  • 4-5 basil leaves
  • 1/2 tablespoon of salt (or less, as per your taste)
  • 1/2 teaspoon of citric acid OR 2 tablespoons of lemon juice

Half this ratio for pint jars.

Sterilizing jars / /Canning tomatoes tutorial // Closet Core Patterns

Once your jar is ready, remove a tomato from the sink and using a paring knife, slip the skin off the tomato into a waiting bowl. I don't bother hacking the little stems off, but you can if you want to.

Peeling & blanching tomatoes// Canning tomatoes tutorial // Closet Core Patterns

Place the funnel in the jar, and start plopping the skinned tomatoes inside. I like to use a wooden spoon to mash the tomatoes as I go so that there are no air pockets. One thing to note: you want  to cool the tomatoes off in the sink so you can handle them, but they should still be somewhat warm. You want to put warm tomatoes in a warm jar, so it doesn't crack when you put it in boiling water later.

How to can tomatoes-16

Stop filling the jar at least 1/2" from the top. The tomatoes will boil vigorously in the canning bath, so give them a little room to breathe.

PH level for safe canning // Canning tomatoes tutorial // Closet Core Patterns

Finally, using a clean washcloth wrung out with hot water, gently wipe just the top edge of the jar to remove tomato residue, as it will interfere with the seal of your jar.

Canning tomatoes tutorial // Closet Core Patterns

Using tongs or the magnetized tool that came with your canning set, remove a lid from the small simmering pot you started earlier and place it on top of the jar. Screw on the accompanying ring, till it is snug but not tight. Air needs to escape from the lid while it's cooking so don't twist it on too tightly. Prepare as many jars as can fit in your canning pot at a time.

Canning tomatoes tutorial // Closet Core PatternsCanning tomatoes tutorial // Closet Core Patterns


How to use a canning pot // Canning tomatoes DIY // Closet Core Patterns

Once your canning pot is at a full boil, fill the rack with your jars. Listen for any cracking or popping sounds; if you hear them, it means a hairline fracture has happened to one of the jars. Find it now and save yourself the aggravation of dumping out a watery tomato stew filled with broken glass later.

Canning pot // Canning tomatoes DIY // Closet Core Patterns

Gently lower the rack to the bottom and make sure the jars are completely covered by at least 1/2" of water. If they're not, top off the pot with water from your kettle.

Process each batch for 45 minutes. You can ready your next batch while the one in the canning pot is cooking. When 45 minutes have passed, gently lift up the rack. Try to do it equally on both sides so you don't tip your jars at an angle; tongs and an oven mitt can help here. Gently remove the jars with the special jar tongs and replace them with the next batch.

Canning tomatoes DIY // Closet Core Patterns

Canned tomatoes recipe // Canning tomatoes tutorial // Closet Core Patterns

Let the jars rest on a towel on the counter overnight. Check to make sure all the jars have sealed once they've cooled down. A sealed jar will have a depressed lid; an unsealed lid will bounce back when you press on it and should be stored in the fridge for immediate use.

Canned tomatoes recipe // Canning tomatoes tutorial // Closet Core Patterns Canned tomatoes recipe // Canning tomatoes tutorial // Closet Core Patterns

If your jars are sticky at all, wipe them down with a wet rag before storing them in your pantry. And then sigh with sweet contentment every time you open your cupboard and see full shelves of summer tomato goodness peering down at you... Your canned tomatoes are good for a year, but chances are they won't last that long.

Please let me know if any of you can your own tomatoes this season! And I'm happy to hear your canning stories, or any tips or tricks for canning tomatoes I may have missed.

Happy canning!

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