How to Can Tomato Sauce

We are fast approaching our tomato quota. Putting up enough tomatoes for the year takes time and effort, a great deal of both, but seeing the end result is more than worth it. This year I am sharing tutorials on how to can peaches, stewed tomatoes and now tomato sauce. While there is already so much information on canning these items both in books and on the internet it is my hope that I can share a few tips to help streamline the process and make it fun.

How many tomatoes? 

You need a large amount of tomatoes to make tomato sauce. The National Center for Home Food Preservation states that you need 35 lbs of tomatoes for 7 quarts of thin sauce and 46 lbs for thick sauce. That's averaging 5 to 6.5 lbs per quart. Of course it depends on the tomatoes. With the Roma tomatoes I picked this year I'm averaging 4 lbs a quart for a medium thick sauce.

What kind of tomatoes?

The best type of tomatoes for making sauce are paste tomatoes. Paste tomatoes are made to be cooked; they have a firm texture, intense flavour, and fewer seeds. There are different varieties of paste tomatoes, also called plum tomatoes. Roma tomatoes are a common variety and affordable. San Marzanos are very good (or so I hear) but may not be as easy to find.

Tip: Spread out the tomatoes in a single layer and let them ripen for a few days (two to five). The tomatoes will be softer and juicer which will make them easier to pass through the vegetable strainer and release more juice. Joel, over at Well Preserved, claims that by doing this you could increase your yield by 10-15%!

Equipment + Ingredients

Quart sized jars (Tip: use regular, not wide mouth)
Lids + Rings
Jar lifter
A large bowl (one or more)
Large pots (two or more)
Vegetable strainer (I use the Kitchenaid fruit/vegetable strainer)
Water bath canning pot + lifter OR Weighted-gauge pressure canner
Ladle + wooden spoon
Funnel (that fits a regular mouth jar)
Old dish rags and dish clothes
Large propane burner + propane tank (optional but worth having)
Bottled lemon juice
Salt (optional)

Setting Up

Gather all the equipment listed above and set up your work space. It's important to have an efficient workspace flow so think about the steps that need to happen and arrange the equipment accordingly. Look through the steps below and envision your work space.

Canning Tomato Sauce

Canning tomato sauce is one of my favourite tomato products to preserve. There is no need to remove the tomato skins. Simply wash the tomatoes and slice them into quarters, and push them through the vegetable strainer.

If your vegetable strainer can handle it, pass the skin and seeds through the strainer again (or a couple times) to squeeze out any remaining juice. The Kitchenaid vegetable strainer has a difficult time handling all the skin and seeds, so after much struggling I opted to skip this step. Tip: If using the Kitchen vegetable strainer place the Kitchenaid mixing bowl below to catch the sauce and large measuring cup beside it to catch the seeds and skin.

Involve your kids! My five year old strained thirty pounds of tomatoes all on his own.

The ensuing tomato goodness will be a little pink and foamy but it will darken when it cooks. Pour the tomato juice into a large pot (or pots) and bring to a boil. Adjust the heat so that the sauce isn't boiling over but is simmering rapidly. Simmer the sauce down until you reach the desired consistency. Boiling the tomato sauce down can take several hours or longer depending on how much sauce there is. 

Ultimately it's up to you to decide how long to boil the sauce. If you want your sauce thin boil it less and if you want it thick boil it longer. I simmer my sauce down by one-third of it's volume which give me a medium consistency sauce. Tip: As the sauce boils down the (in)sides of the pot will be covered with a thick tomato paste, be sure to scrape the paste and mix it back into the sauce.

When the sauce is ready to can clean and rinse the quart jars and prepare the lids. In each quart add 2 Tbsp. of bottle lemon juice and 1 tsp. of pickling salt. The salt is optional but the lemon juice is not optional. Lemon juice ensures that the tomatoes are acidic enough to can safely (for more information read the NCHFP acidification instructions).

Fill each jar with hot tomato sauce leaving 1/2 inch head space. Wipe the rims and place the lids according to the manufacturers instructions and tighten the metal rings to finger tip tight. Process quart jars of tomato sauce in a water bath canner for 40 minutes (45 minutes if above 1000 ft elevation) OR for 15 minutes at 10 lbs of pressure (15 minutes at 15 pounds of pressure if above 1000 ft elevation) in a weighted-gauge pressure canner. If using a water bath canner please ensure that the water come to a rolling boil before timing. These processing times are the same as those recommended from the National Center for Food Preservation for tomato sauce.