Processing food for canning – how to can tomatoes without waste

Stop me if you’ve been here – you have a big pile of gorgeous produce and you’re going to turn it into jars and jars of food. Sounds good, right? You envision shelves full of canned tomatoes or sauce. You think surely the 25 pound box of tomatoes you just bought at the farm stand will help you fill those shelves. And then you spend hours peeling, coring, chopping, simmering, etc only to end up with….three quarts of sauce or a few pints crushed tomatoes.

Where did those pounds and pounds of tomatoes go?! The answer is (likely) that most of their mass ended up evaporated. Now it’s a fact that even denser paste tomatoes have a lot of water. So even with super efficient processing, 25 pounds of tomatoes isn’t going to yield 25 pounds of sauce or crushed maters. But here’s one way to process those tomatoes and capture as much of their goodness as possible. These tips will help you see how to can tomatoes without waste or at least with less waste.

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How to can tomatoes

First, let’s talk about your options when it comes to canning tomatoes.

Tomatoes can be canned in all the following way (note, I’m not delving into recipes that include tomatoes, like salsa, just tomatoes themselves)

  • whole (peeled)
  • halved or quartered (peeled)
  • crushed or cubed (peeled and cored)
  • sauced or pureed (usually peeled, often cored)
  • tomato juice

All of these methods are similar. Tomatoes are usually peeled, though it’s not a strict requirement. Peels can be tough or throw off the texture of sauces or other dishes.

Always use clean, ripe tomatoes that have no blemishes or signs of rot. Many people prefer to can paste tomatoes like Romas or Amish Paste because they have more flesh and less juice. But you can use any variety of tomato for canning.

How to add acid for canned tomatoes

Tomatoes are ‘hot packed’, meaning they are heated in a pan with water or juice, then poured into hot canning jars. Each jar needs added acid, either from bottled lemon juice or citric acid. Modern tomatoes may not be acidic enough by themselves, so the extra acid is necessary to ensure botulism spores can’t develop.

Use 1 tablespoon of lemon juice (or 1/4 teaspoon of citric acid) per pint and 2 tablespoons (or 1/2 teaspoon of citric acid) per quart.

Using citric acid in canning

Whether you use lemon juice or citric acid is a matter of taste. I use lemon juice when I can Bloody Mary Mix, since lemon juice is an ingredient anyway. For crushed or sauced tomatoes, I prefer citric acid because it doesn’t change the flavor. You can buy citric acid in most grocery stores but I prefer to grab a 5 pound bag from indie bulk grocer Azure Standard. It’s cheaper and lasts me for years. (Related: read my review of Azure Standard.

The jars are then processed in a water bath or pressure canner. Processing time varies based on the tomato preparation and whether you’re using quart or pint jars. At the end of the post, I’ve included links to processing methods and times for tomatoes from the National Center for Home Food Preservation.


Wondering if it’s really worth it to can food? After all, you’ve got to buy  canning supplies like jars, lids and maybe even a pressure canner. And there’s all the prep work. Check out my honest assessment Is Canning Food Worth It? It includes my numbers breakdown for processing and canning 25 lbs of green beans.


How to pick the best method for canning tomatoes

There’s nothing wrong with any of the tomato methods just listed. Whole tomatoes are more versatile, since you’re leaving most of the tomato intact. On the other hand, they’ll also require the most processing once you open that jar. Crushed tomatoes won’t need as much future processing but they’re a little less versatile, at least to some folks. Turning tomatoes into sauce means you have a jar of highly concentrated tomato flesh that’s just about ready to become spaghetti sauce or chili base. But processing tomatoes into sauce takes the most time.

The best way to decide how to process your tomatoes is to think about how you plan to use the canned products later. If you’re not sure how you’ll use them and want to keep your options open, whole or halved is probably best. Those large tomatoes can be simmered into sauce later or drained and chopped for salsa. On the other hand, if you mostly use canned tomatoes for red sauces or soup bases, you might want to go ahead and process your tomatoes as crushed or sauced. Remember that canning fresh food isn’t just food preservation. It’s also food preparation. So it can be really helpful to just go ahead and fully process all at once.

And, of course, you don’t have to do all your tomatoes the same way. It’s smart to process them in a variety of ways, if you think you’ll use them.

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How to peel tomatoes easily

There’s basically two manual ways to get the peels of your tomatoes before you process them.

Freeze tomatoes for peeling

Take the tomato, put it on a plate or cookie sheet, stick it in the freezer. When the tomato thaws, the skin slides right off. This method is great if you’re growing your own tomatoes and harvesting them a few at a time. It’s also great if you just can’t bear the idea of heating up a bunch of water in the middle of summer. The downside is you might not have enough room in your freezer to accommodate a big batch. (and remember, the point of this post is efficiently processing big batches)

Boil tomatoes for peeling

In the interest of being candid, I hate this method. It’s hot and annoying. But boy howdy, it works and it works fast. Bring a big pot of water to a boil. Cut an X into your tomato and toss it  (carefully) into the water. After a minute or two, remove it and plunge it into ice water. Once the tomato is cool enough to handle, the skin slides off. With a large enough pot, you can peel all your tomatoes in just a few minutes.

Strictly speaking, you can also roast tomatoes at 400 degrees for 30-60 minutes and then remove the peels. While roasting is a great way to concentrate tomato flavor, waiting for them to cool so you can peel them is a little tiresome. If you’re going to roast them anyway, then you can either freeze or boil them to peel or you can peel them after roasting.

Ugh, both of those methods sound awful. Is there any other way?

Yes. You can use a food mill. A food mill will remove the skin and seeds, as well as the tough core, from tomatoes. The tomatoes can be raw, cooked or somewhere in between. If you’re making tomato sauce or juice, this is a great option. Some food mills include a larger screen, so you can also use the mill to peel tomatoes you plan to crush.

If you’re going to can whole tomatoes or tomatoes in large chunks, skip the food mill.

Canning whole, halved or quartered tomatoes with less waste

There isn’t a lot to suggest here, actually. Canning whole tomatoes is pretty low-waste since you’re using the entire fruit (less skin).

BUT you can use that discarded tomato skin! As you remove the skin, toss it into a colander or strainer. Tomato skin usually comes off in large pieces, if you peel using the freezer or boiling methods. Spread those skins out on a baking sheet (line with parchment paper) or put them in your food dehydrator. Process on very low heat (175 in the oven or 105 in the dehydrator). Once they’re fully dry, whirl them around in a blender, food processor or grinder and you’ve got tomato powder. The powder is a great way to thicken up or flavor other dishes.

If you don’t want to mess with drying tomato peels, feed them to your chickens or your composting worms or use them to infuse vinegar.

Canning crushed or sauced tomatoes with less waste

This is where it gets interesting! First, peel the tomatoes or use the food mill to remove skins and seeds. Note that if you want to dry the skins, you shouldn’t use the food mill.

Some food mills have multiple screens so you can process tomatoes in chunkier or finer sizes. If you ultimately want larger chunks of tomatoes, make sure your food mill can accommodate that. Otherwise, process them by hand.

Processing by hand

Remove the tomato skins and prepare them for drying if you wish. Then remove the seeds and core. While you can use a paring  knife or spoon for this, I’ve found it’s just easier to give the tomato a gentle squeeze and pull the glop out by hand. Throw the glop (that’s the technical term) and seeds into a very fine mesh strainer, placed over a bowl. Make sure the strainer sits securely in the bowl. Gently press and stir the glop to release more tomato juice.

Optional – put your diced tomatoes in a different fine strainer over a bowl and let some of the tomato water and juice drain out. While you need some water or juice in the jar with the tomatoes, you probably won’t need the full amount, especially if your maters are really juicy.

Reserve the collected juice for other uses, like Bloody Marys. Either discard the seeds or feed them to your worms or chickens.

Processing with the food mill

Some folks say their food mills can handle large, raw tomatoes. My food mill, which is pretty stout, can technically process big, raw tomato chunks but it takes a LOT of cranking and pushing. I’ve found I get better and faster results if I prep my tomatoes in one of the following ways:

  • quarter the tomato and give them a pulse in the food processor
  • quarter the tomato and give them a quick dunk if boiling water
  • quarter the tomato and roast them at 400 for 45 minutes (only if I’m processing for sauce or salsa)

I could just chop my tomatoes up and feed them to the mill but I’d lose a lot of juice. And I want that juice. I also don’t want to have to keep wiping it up as it inevitably runs off the cutting board.

The food mill will separate the tomato pulp and juice from the seeds and peel. I usually run the ‘waste’ through the mill a second time to make sure I’ve gotten everything out. From there, the waste (which is usually quite minimal since the mill is very efficient) goes to…..the chickens or the worms.


Sidebar: You need a worm bin

While you might not want chickens or be able to have them, almost anyone can set up a small worn bin for vermicomposting. I highly recommend that as a waste mitigation and soil enrichment strategy.


I put the pulp into a fine mesh strainer and let the juice slowly seep out. Whichever method you use, put the strained juice into a pan and let it simmer a bit to thicken up slightly. Use it to pack your chopped or crushed tomatoes. Any leftover juice can be canned, frozen or enjoyed fresh (did I mention how much better a Bloody Mary is when it’s made with super fresh juice? No? It is.)

Turning tomatoes into sauce with less waste

This is my favorite because it yields so many different tomato products. Tomato sauce is notorious for it’s long simmer time. While simmering helps develop and concentrate flavors, it can get really tiresome having to keep a pot on the stove for 12-18 hours. Plus that simmering time is just evaporating out the juices, which you can use for other things (besides Bloody Marys).

There are two schools of thought when it comes to processing tomatoes into tomato sauce.

School #1 says that it’s best to remove all the seeds and peel. The second school of thought says it’s a lot easier to just puree the entire tomato since the blades will pulverize both skin and seeds. I say both methods are fine but if I have time, I prefer to remove the seeds and peel.

Food Mill 

If you want to dry the tomato peels, boil or freeze the tomatoes to peel them. Otherwise, process them in the food mill unpeeled. As noted above, it’s usually easier to process tomatoes if you coarsely chop them, blanch them or wizz them in the food processor briefly. Feed the tomatoes through the mill. Collect the tomato pulp and put it into a fine mesh strainer over a bowl. Gently stir and press the bulb so all the water and juice drains out. Simmer the strained pulp until it reaches your preferred consistency, then can. Either can, freeze or enjoy the tomato juice.

Tomato sauce with seeds and peel

First, you can remove the peels using either the boiling or freezing method. Or you can just process the peel. I’ve done both and discovered that while most of the peel will breakdown, there are usually some strips left in the sauce. If that doesn’t bother you, no need to peel the tomatoes.

Quarter the tomatoes (peeled or otherwise) and put them in a food processor or blender. Process until they’re a soupy, pulpy mess. The further you are able to process them, the finer your sauce. Once you’ve processed the tomatoes, put them into a fine strainer over a bowl and let them water and juices drain out. Gently stir and press the pulp so all the water and juice drains out. Simmer the strained pulp until it reaches your preferred consistency, then can. Either can, freeze or enjoy the tomato juice.

Below, the peels, seeds and cores from about 15 pounds of tomatoes. I feed them to my chickens but as noted above, I could have peeled the tomatoes separately and dried the peels.

tomato skin and pulp
Tomato sauce sans seeds and peel

Manually

Use the freezing or boiling method to peel the tomatoes. As noted above, retain the peels and dry them to make tomato powder or use them to infuse vinegar. Then cut the tomato in half and manually remove the core and seeds. You’ll have a hard time getting every single seed, but you can get a lot of them. Put the seed glop in a finer strainer placed over a bowl. Gently press the glop to release any juices.

Put the tomato pulp into a fine strainer over a bowl. Gently press and stir it until the water and juice has drained out. Process the tomato pulp in a blender or food processor for the finest texture. Then simmer the saucy pulp until it reaches your preferred consistency. Pack in to hot jars and process. Either can, freeze or drink the juice.

Below you can see the tomato pulp after most of the juice has drained away.

Canning Tomato Sauce – thick or thin?

When you strain and separate the tomato pulp and juice, you’re ensuring your sauce will be very thick. This is excellent for future uses like spaghetti or lasagna sauce or other recipes that need a denser tomato base. But what if you don’t want your sauce to be quite so thick? Tomato sauce for soup or chili needs a little more juice. Or maybe you just want to can thinner tomato sauce so you can the option to simmer it down with other ingredients later.

No problem! Just add some of that juice back into the pot with your strained pulp. Simmer it all together and check the consistency. If necessary, add more juice until you get the tomato sauce to your desired consistency.

You can also simply skin straining some of the juice and pulp or use an even finer strainer, like cheese cloth. The finer cloth will capture more of the tomato juice while still letting some of the watery juice escape.

How much tomato sauce do you get from 25 pounds of tomatoes?

When I process the tomatoes as described above, and strain all the juice out, I end up with 2 quarts of thick sauce and 6 quarts of juice. When I don’t strain the juice out as much, I end up with 3-4 quarts of sauce and 2-3 quarts of juice.

Keep in mind the tomato juice is a byproduct of processing the tomatoes. I’m capturing the liquid that would normally be simmered away.


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Canning tomatoes the easy way

Processing tomatoes and taking extra steps in order to extract as much from the fruit as possible obviously makes the process take longer. If you’re not keen on that, no worries. It’s totally fine to tackle your tomatoes in the way that works best for you. Sometimes that might mean saving skins and extracting juice and sometimes it might mean chucking everything in the jar and into the canner. There’s no wrong way to preserve food!

Here’s what the National Center for Home Food Preservation has to say about canning tomatoes.

And here are a few of the most common tomato canning methods. Even if you take some of these extra processing steps, the NCHFP methods included at these links are still the gold standard of good and safe canning practices.

How to Can Whole Tomatoes

How to Can Crushed Tomatoes

How to Can Tomato Sauce

How to Can Tomato Juice