Sunday, September 27, 2009

Canning Crushed Tomatoes

Canning tomatoes is a huge part of the end of the summer season for me and my cooking year round. Canning tomatoes makes me feel smug in the middle of winter as I continue to cook with tomatoes from my garden. Yes you can find canned tomatoes in the supermarkets, however these are better, and local. Part of the appeal is also gazing at the rows of jars lined up in the basement. My last kitchen was huge and I used to leave any canning projects out for several days, just so I could admire them. Now I have to do my gazing in the basement.

My tomatoes did end up with the late blight that has been troubling the North East this summer. However at this point in the season the recommendation is to remove diseased leaves and branches without disposing of the whole plant, so some tomatoes have still been available to harvest. In addition I bought some tomatoes from a local farm. I was just a little worried at not having rows of tomatoes to stare at all winter. After canning tomatoes for home use for the last 2 years I realized that I like the crushed ones the best. They are versatile enough to be used in stews, spaghetti sauce, pizza sauce and soup and they have already cooked down slightly so they are more convenient. With 28 jars of crushed tomatoes preserved if I have any more tomatoes to can this year, the rest I will do as tomatoes halved or quartered in their own juice.

As with any canning project there are some important steps to follow to eliminate safety concerns. For example you can not add any other vegetable to the tomatoes because that would lower the acidity of the finished product. Foods that are high in acid prevent the growth of botulism, a deadly toxin that is tasteless and odorless. Tomatoes are borderline acidic so to safely can them you need to add acid. You can add vinegar, lemon juice or citric acid to make tomatoes safe to can. I use citric acid as it does not affect the flavor of the tomatoes. You can find citric acid in the canning section of your grocery store, in the bulk food section of many stores (such as City Market here) and in the kosher food section of stores. It is also marked as "sour salt."

Tomatoes are one of the most common home canned items for people to insist on using the methods their families have always used, insisting that there has not been a problem yet so why change. My feeling on this is there was not a problem in the past because there were no botulism spores present when they canned tomatoes in the past.  If you never get in a car accident it is also perfectly safe to not wear a seat belt.

You may notice in the photo of my canning set up that I do not heat my lids in hot water. This step is not needed for safety, as hot water that is not boiling would not sterilize anything. Instead it is supposed to soften the compound on the lid so it will seal. However if you put the jar in a boiling water bath I have found the lids get plenty hot and seal. Somehow that last pot of boiling water on the stove was the one that made canning seem complicated.

Canning Crushed Tomatoes

Tomatoes, 1 pick your own flat should fill about 3-4 quart sized jars. Two flats is one canner load or 7 jars, but you need a very large stock pot to crush the tomatoes in.
Citric acid or bottled lemon juice (fresh juice has inconsistent acidity) or 5% acidity vinegar

1 canning pot or a large stock pot
1 rack to lift the jars of the bottom of the pot (the rack is necesary to prevent the jars from breaking from the heat, you can also use a round cake rack or Macgyver one from jar rings wired together. I have used a dishtowel in the bottom of the pan and vowed never to do that again. A friend of mine reported on a canning endeavor that ended with green water from the dye in the dishtowel.)
jar lifters (you can make do with tongs but it is awkward and not really worth it)
1 canning funnel
canning jars, lids and rings (I usually use quarts for tomatoes)
1 ladle
1 potato masher (or wooden mallet or spoon or equivalent for crushing the tomatoes)
1/2 tsp measure if using citric acid and quart jars
large stockpot, large enough to fit al the tomatoes you wish to can
clean receiving blanket or dish towel to put on the counter so the jars are cushioned from the counter (I found that receiving blankets are the perfect weight and thickness for this)

Start by peeling the tomatoes by blanching them first and then removing their cores while cutting into quarters. Place the peeled, cored quartered tomatoes in a large stockpot until you have a double layer of tomatoes covering the bottom of the pan

Use a potato masher or a wooden mallet or spoon to crush the tomatoes in the pot. Heat the tomatoes that are already crushed, stirring occasionally to prevent sticking, while you continue to peel, core and cut the remaining tomatoes. Add tomatoes to the pot as you go, there is no need to crush them as the heat will break them down. Once the tomatoes are all added boil gently for a minimum of five minutes (longer will give you a more reduced tomato product).

While the tomatoes are heating fill your canning pot with water and wash the canning jars, adding them to the pot. The water in the canning pot should be above the top of the jars. Heat the canning pot of water and jars while you wash the lids and rings and lay them out on the receiving blanket or dish towel.

Use the jar lifters to remove the jars from the hot water and empty water from the jars. Fill the jars with hot crushed tomatoes leaving 1/2 inch of headspace (that means fill the jars all the way to 1/2 inch from the top of the jars). If you want add 1 tsp of salt per quart jar (I never do as I want the flexibility to add salt when I am cooking with them later). Acidify the jars by adding citric acid, bottled lemon juice or vinegar to the jars. Quart jars get 1/2 tsp citric acid, or 2 Tbsp bottled lemon juice or 4 Tbsp 5% acidity vinegar. Pint jars get half that (1/4 tsp citric acid or 1 Tbsp lemon juice or 2 Tbsp vinegar) and 1/2 pint jars half that (1/8 tsp citric acid or 1 1/2 tsp lemon juice or 1 Tbsp vinegar)

Wipe the rims of the jars with a damp paper towel before putting on the lid and rings. You also should come up with a method that helps you to keep track of proper acidification of the jars. The method that works for me is filling a whole group of jars with crushed tomatoes, cleaning all the rims and then adding citric acid to all of them before placing on the lids and rings and adding to the canner.

When all the jars are filled and in the canner measure to make sure the water covers the jars by at least 1 1/2 inches. Put the cover on the canner and turn to the heat to high. Bring to a boil and start the timer after the water is at a full boil. For altitudes of 0 - 1,000 ft boil jars for 35 minutes for pints and 45 minutes for quarts. If you are at a higher altitude you can refer to this chart for processing times, the chart also shows times for processing in a pressure canner. You can lower the heat so long as the water is always maintained at a complete boil for the entire processing time.

Keep the canner covered until for the full processing time. Once the jars have boiled for the appropriate length of time turn off the heat, remove the canner lid, and set a timer for 5 minutes. After the five minutes use a jar lifter to remove the jars from the canner to the receiving blanket or dishtowel, leaving at least 1 inch of space between jars.

leave the jars undisturbed while they cool (resist the urge to press on the lids to see if they sealed). Do not tighten the rings while cooling.

After the jars have completely cooled (12 to 24 hours) remove the rings, wash the lids and jars and test the seal, the center of the lid should be down and the lid should not pry off easily with your fingers. If the lid comes off of any of the jars store those in the fridge and use first or add to the next batch of crushed tomatoes you are heating to can.

Store in a cool, dry place out of direct light after you have admired them for an appropriate length of time. Use all year to make sauce, soup, added to braises etc.


  1. Great post! Exactly what was needed and lots of time between now and next season to think about it. :)

  2. Great post. I just finished canning salsa today. It was the first time I ever canned. Pretty proud of myself. My next step is to try canning apple pie filling.

  3. Marti, I am so glad you like the post. It took a while to write and I thought about waiting until next year to post it, then I figured my plants have one more good run left so others might need it.

    Cory, There is something about canning that is weirdly addictive and satisfying. I always feel so proud when I have finished. Just so you know when you go to can the apple pie filling that the only safe thickener for pie filling is clearjel. other thickeners (flour, cornstarch ect) can break down when canned and also can prevent the proper heat penetration for a safe product. Plus they can change the PH. Personally I would just can the filling without the thickener and then add it when baking the pie. I don't see any need for it to be thick in the jars.

    If you want to use clearjel here is more info about it and sites where you can buy it:

    clearjel info


  4. Thanks for this post! I'm canning my first crushed tomatoes tonight.

  5. As I was cruising around, I came upon this recipe for making dilly green tomatoes. I'm thinking of using it for all of the little grape tomatoes I'll have left on the vine soon. Do you think it's a safe one to use?

  6. Katherine, The basic recipe is fine, green tomatoes don't need as much vinegar to safely pickle them as cucumbers do because they are higher in acid themselves. However they do need to be processed in a water bath canner for 15 minutes for quart jars. Here is a tested dilly tomato recipe on the National Center for Home Food Preservation web site.

    I also posted a lacto fermented green tomato pickle last year. If i make them again this year I plan on leaving out the hot pepper, I did not like it in the finished product.


  7. Last canning season I purchased a steam canner. Love it! The jars don't sit in a water bath, but they process the same amount of time. Some say you must use a pressure canner for all vegetables, but I used to open kettle my tomatoes, and never had a problem. This years I'll use this recipe for crushed tomatoes, as here in Texas we have also be plagued with tomato blight. Thanks for the tip.