canning and preserving: whole tomatoes

Last week with our CSA, we did an add-on and bought a case of canning tomatoes. This is one of the great perks of a CSA – having an “in” when it’s harvest time and there are extras. But at the same time, you have to move quickly and preserve them before they turn. So we took our annual spur of the moment “canning vacation day” to get some whole tomatoes put away. 


Tomatoes do freeze, so why do we bother with canning? Because home canned tomatoes are delicious – and don’t require any defrosting. They are great in pasta sauces or chilis or any number of other dishes that would have you buying canned tomatoes at the store. We still do freeze tomatoes from time to time, but canning is our preferred tomato preservation method. 

We decided to do quarts, since it’s roughly what you’d need when a recipe calls for a 28 oz. can of tomatoes (as there’s more liquid in home-canned tomatoes).


We also had a ton of extra Beam’s Yellow Pear Tomatoes from our own garden. So far they’ve been the only ones to actually ripen on the vine, though we’re having some success ripening the others indoors. Leftover from the CSA, we also had some cherry tomatoes that we threw in the mix.


For any canning or freezing project where you’re preserving tomatoes, the first thing you need to do after washing the tomatoes is remove the skins. You do this by first cutting an X in the bottom of the tomatoes. For larger tomatoes, also remove the core.






Next, you blanch. Boil some water and drop the tomatoes in for 30-60 seconds depending on the size of the tomato.


After their dip, pull them out and immediately dump them in an ice bath. This will make it so the skins fall right off.

Once the skins are removed, they look like wrinkly raisins. This time around we did all of the skinning first, so that we didn’t have to keep repeating the set up. (Canning is often a dance of multiple pots, containers and bowls all over your kitchen.) 


For large tomatoes, cut into quarters. (It helps them fit into the jar better, and it also helps you crush them later for sauces, etc.)


Pack them into jars with boiling water and citric acid. (Tomatoes in a water bath canner need citric acid to ensure the acid content is high enough to kill all the bad stuff.) 


Leave the appropriate headspace and close the jars with hot lids and bands.


Process them according to the directions, and then open the canner. And find…


A broken jar and floating, delicious wasted tomatoes. Yep, of 12 quarts we tried to can, we broke a jar in each batch. Clean slice, right across the bottom. (But obviously you can’t eat the floaters, since glass shards are not considered edible.)


We’ve canned hundreds of jars of food since we started doing this three years ago and we’d only ever broken one jar before, I believe. So why two this time? Any why tomatoes?

We did some research and realized that because our jars were sound and not cracked or splintered, it was probably due to temperature. When you make jam, you pack hot jam into hot jars and drop them into the hot water bath, so the temperature of the jar remains relatively constant during the canning process. 

For tomatoes, we cold pack. That means that hot jars get filled with room temperature (“cold”) tomatoes and boiling water, but that water quickly cools inside the jar while you’re packing and measuring headspace and sealing. We added the jars straight into a boiling canning pot, which means some of the jars were probably too “cold” and got shocked into the clean break you see in the photo. The way to avoid this when you’re cold packing is to wait to bring the canner to boiling until the jars are all ready, so the temperatures can gradually rise and the differential isn’t too large to cause a break.

While it’s frustrating to lose two quarts of perfect tomatoes, I don’t mind making mistakes when we can figure out what went wrong. That way we avoid it next time. I’m just grateful for the 10 quarts we managed to save!