Canning Tomatoes

Posted by on September 14, 2009 at 9:23 pm.


I should preface this by saying I am not a fan of canning sauce.  Tomato sauce is so easy to make from canned tomatoes I really don’t see the need to make it early.  I only ever keep whole canned tomatoes in my kitchen, so I only ever make whole canned tomatoes.  This leaves me with endless last minute options (soups, stews, pasta sauce, pizza sauce, spicy sauce, garlic sauce, basil sauce, onion sauce, vodka sauce! etc). Not to mention, I can really only handle eating so many of the same thing.  I like variety!


So I am on my third year of canning tomatoes, and each year I learn a little something new.  My first year, the most important thing I learned is that raw packing is not awesome or time saving.  First, you can’t fit as many tomatoes in one jar when you raw pack, they are too stiff and filled with air, leaving them floating in more than half a jar of water. Not only does it look a little sad, but it takes up more room than necessary and you need to use more than one jar for just about any recipe.  Second, it is extremely easy to break a jar when doing raw pack.  You can’t place them in hot water, you have to water process them in cold water, which takes forever to heat up, and ends up not being a time saver at all.  I also learned that bottled lemon juice tastes like chemicals, even it’s organic with no additives, and that non-sauce tomatoes do not hold their texture after being processed.  So my second year I felt I was going into it well informed with everything sorted and ready to go.  I bought a variety of tomatoes (heirloom seconds that were bruised or split) and about 20 lbs of sauce tomatoes. I used citric acid (sour salt!) instead of lemon juice to preserve the flavor, and I cooked and blended the heirlooms which I strained for juice and used to pack the sauce tomatoes.  It was especially lovely since many of the heirlooms were Purple Russians.   Unfortunately, I had a lot of extra juice left.  Fortunately, I saved it and used it to pack a bunch of cherry tomatoes, but I sort of made the decision then that this was not the best way to go. It is potentially very wasteful.  What I realized is that I ultimately want stewed tomatoes packed in nothing but themselves.  My favorite can of tomatoes has always been San Marzano, not just because the variety of tomato is fantastic, but also because they are packed in nothing but juice, salt, and citric acid; so this year when Mariquita Farm said they would be in Capitola, I knew exactly what I wanted to do.  I ordered 40lbs of tomatoes and set to work finding a recipe that would work for me.


Let me explain a little bit about canning tomatoes.  I don’t often work from recipes, but certain things require at least a point of reference if for no other reason than to be safe.  In the 80s, the USDA revised their standards for canning tomatoes based on new varieties which were bred to be more meaty and less acidic. This means that the safe level of acidity you need to process tomatoes as “high acid canning” in a water bath was no longer standard or certain.  According to new standards, when water processing any sort of canned tomato product, you are required to boost the acid levels to a safe standard of 4.6 PH or lower (I know that sounds weird, but higher acid content means lower PH).  The NDSU extension service researched this and found that not a single variety of tomato they tested had sufficient acid levels to defeat the growth of clostridium botulinum, the bacteria that causes botulism. Botulism freaks me out. I don’t mind admitting it, and I think even people in the Slow Food movement (see Eugenia Bone’s comment about old Brandied Peaches recipes in the New York Times last month) can agree that going back to older methods on this are not necessarily the best.  It is true, that many people have had great results using family recipes that have been passed down for generations. It is also true that many of these people are also using seeds and growing methods that have been passed down just as long. I am not that fortunate. I also know that the way a person grows their tomatoes greatly effects the flavor and acid levels of their tomatoes.  Variety isn’t enough. Think about dry farm vs standard tomatoes, or how heirlooms split after a hard rain. It is important to find a recipe that has had it’s acid levels tested on a wide variety of tomatoes. This is why there are very few variations on the methods for canning tomatoes. What I was hoping to find was a recipe that took into account hot packing tomatoes in their own juice, and possibly find one that called for reducing it to a safe level where I would not longer need to add citric acid or I could add less.  I found nothing.  As far as canning whole tomatoes, there are only the standard recipes: hot pack in water, raw pack in water, raw pack in juice, and stewed tomatoes with onions, garlic, and peppers.  I ended up using the raw pack in juice recipe for my acid levels since it is the most similar.  My gut feeling is that you could probably reduce it for about 20 minutes and add less or no citric acid, but since I couldn’t find anything to confirm this, and I’m afraid of botulism I went with the standard 1/2 teaspoon per quart.  Below is the recipe I created accompanied by a LOT of photographs.  You can see the recipe without the essay here if you are familiar with canning already. Or, if you are looking to trouble-shoot, check out the Q & A.

Stewed Tomatoes Packed In Their Own Juice

A couple things to keep in mind before we get started. You can can any tomatoes using this method, though it has been my experience that sauce or paste tomatoes will hold their form best and blanch easiest.  I have had the best luck using Striped Roman Tomatoes or San Marzano tomatoes, though I can say without hesitation that San Marzano tomatoes have a superior flavor in any circumstance.  Also, in the interest of being safe, do not adjust the citric acid levels  in this recipe for any reason, and do not replace the juice, or top of the jars, with water.  Maintaining a low PH is extremely important for safe preserving.

What You Need

  • 20 lbs of tomatoes
  • citric acid (you can buy this at your local home brew store)
  • salt
  • ice
  • canning pot or other 5 gallon pot
  • canning rack or appropriately sized cake rack
  • canning tongs (seriously, you have to have them)
  • large soup or stock pot (stainless steel, enameled, or otherwise coated – do not use aluminum or copper)
  • slotted spoon (recommended but optional)
  • ladle
  • canning funnel (recommended but optional)
  • 8-10 quart jars

Process Summary

  • start your water bath
  • start your blanching pot
  • wash tomatoes
  • make your cold water bath
  • blanch tomatoes
  • stew tomatoes and prepare jars
  • pack tomatoes
  • process jars

Start your water baths

Before you do anything else, you should start your water baths. You will need one large bath (5 gallons or larger is recommended) to process the quart jars, and one smaller bath to blanch your tomatoes.  By the time your blanching bath is ready you will be ready to use it, but the water bath for processing your jars can either be turned off or set to simmer depending on how fast you work. These are the three pots I used. The left most pot is my caner, the stainless steel pot I used to cook the tomatoes, and the smaller pot (about 8 quarts) I used to blanch the tomatoes.


Wash your tomatoes and make your cold water bath

You may not need to wash your tomatoes, but if they are covered in dirt, or have mold on them you should.  Blanching them will definitely remove any dirt and kill any mold, but it will also get in your tomatoes if they split.  The way blanching works is by heating the outer most part of your fruit which softens the flesh under the skin. The flesh releases juice that helps to separate the skin from the flesh.  When you toss them into cold or icy water, it simultaneously stops the tomato from cooking further and shocks the skin into releasing the flesh entirely.  You’ll notice as you go when you have done this exactly right because you will lose the least amount of flesh from the tomato while still being able to slide the skin off effortlessly. You do not need to have a cold water bath, but you should have at least a room temperature bath to cool the tomatoes enough to handle. Set up a bowl and your stock pot next to the sink to catch the tomatoes and discard the skins.


Blanching the tomatoes

Removing the skin is an important culinary part of canning tomatoes.  The skin will make any sauce or soup you make astringent, meaning it will have a sharper bite and very likely curdle milk, making your tomatoes less versatile.  I have met a lot of people over the years who go out of their way to skip this part (even so far as blend their sauce in lieu of blanching or milling).  To me, this is the most fun of the entire process. It is incredibly satisfying to slip the skin of a softened warm tomato.  Maybe it’s because I know it’s the closest I get to cleaning or trimming meat, or maybe there is just something satisfying about removing thin membranes (elmer’s glue anyone?). The bottom line is that this is an incredibly easy process, and you have to wait for your water bath to heat up anyway.  You really might as well.


You start by heating your blanching bath to a rolling boil and slipping in (gently! no splashes!) about 10 tomatoes.  Cover them and let them simmer for about 30 seconds (don’t worry if you don’t want to set a timer, nothing terrible will happen if its too long).  Remove them with a slotted spoon and dump them into your cold water bath, covering the lid until it reaches a rolling boil again.  Now you can begin slipping the skin off.  Using a sharp paring knife nick the stem end of your tomato and, either using your finger nails or the knife tip, lift up a part of the skin and peel it away.  Now you should be able to pinch the rest of the skin off, or at least remove it quickly by peeling it away.  Toss the tomato in the pot you plan to cook them in and the skin in a bowl.  Add more tomatoes as the water heats, and continue until every tomato is blanched.  Don’t worry too much about working quickly, you can always do all the peeling at once at the end.  Below is a video of me removing the skin:


Stew the tomatoes and prepare your jars

Once the tomatoes are peeled you can begin cooking them on low heat until they begin to release some juice.  Stir them occasionally to make sure they aren’t sticking, and if your pot isn’t large enough to make this easy, separate them into two batches.  When enough juice has released you can turn the temperature up, cooking until they are covered with juice and slowing boiling.



While your tomatoes are cooking, wash and prepare your jars.  Remove the bands and place them over a beer bottle for easy grabbing.  Remove the lids and place them in a bowl or pan to be filled with warm water.


NOTA BENE: any canning site that tells you to boil your lids should be blacklisted. I mean it. Boiling lids destroys the seals and causes them to rust. Anyone who instructs you to do so is an amateur and likely using unsafe methods. It is the number one sure fire way to know if you can trust an author or recipe.  Keep your lids in hot water, think warmer than bath water but not scalding, and don’t bother heating them until just before you begin ladling.  The idea is to soften the seals so they fit properly against the glass, but also easily allow air to escape in the water bath processing so they don’t explode from the expansion.  Later, as the jars cool, the seals begin to firm up and help create the vacuum seal.


If you have a dishwasher, you can put jars through a wash cycle and let them sit in the hot steam. This is ideal, but I haven’t lived some place with a dishwasher in at least 10 years, so if you are like me, just wash them by hand and set them on a rack to dry.  Then, just before you begin ladling you will add 1/2 teaspoon of sea salt and 1/2 teaspoon of citric acid to the bottom of each quart jar (half that for pints).  The salt is optional, you do not need it for preserving, but I can guarantee you that adding salt while cooking is always better for flavor than adding it afterward.


I used gray Celtic sea salt, which I love so much so I lick it off my fingertips.  Even if you don’t like a lot of salt, at least use some. Trust me, it will make a difference.  You will want to set your jars up next to the stove.  Get everything ready so you don’t surprise yourself.  Place a rag across the gap between your stove and the counter to catch drips.  Get the ladle out, place your canning funnel in the first jar, pour warm water over the lids, and keep the rings close by.


Packing your jars

This section is pretty straight forward. The only confusion tends to be how full to pack your jars.  When working with whole fruits or vegetables, you will want to leave more head space to allow for expansion.  Whole fruits and vegetables like canning tomatoes or making pickles (as opposed to jams, jellies, or juices) contain a lot of air in them that will expand in the water bath processor.  If you don’t leave sufficient head space liquid will be forced out of your jars and possibly compromise your seals.  To be perfectly honest, I have never had a seal fail and I have definitely over filled my jars.  The worst that has happened is that my jars smell like vinegar or come out with a thin sticky film.  Still, both of those things are annoying enough to warrant a little care in this area.  For whole (or halved or pieces of) tomatoes, as well as pickles or whole fruits in syrups you will want to leave at least 1 inch of head space.  It should look something like this:


Any higher and you are risking sticky smelly jars and possibly a failed seal.  Still, don’t worry so much about it that you stop enjoying the process.  Don’t spend so much time trying to even it out that your jars cool off!  At this point, you will want to make sure your water bath is simmering again.  Ladle the stewed tomatoes into your jars on top of the 1/2 t. of citric acid and 1 t. salt.  Place the lids on top and screw the bands on firmly, but without wrenching them super tight.  You should have between 8-10 jars depending on your tomatoes and your head space.  If you have a short jar, you can set it aside in your refrigerator for later, or use a pint jar instead.

Processing your jars

If you are using a traditional caner and rack, let me be the first to warn you if it is your first time. DON’T LOAD IT UNEVENLY. IT WILL TIP OVER.  Be careful! Try to load two jars at a time, opposite each other.  Place one in the center first.  Use the rack handles over the sides of your caner so you don’t have to place them fully in the water. You can use pot holders to place them in the rack if the lids are hot.  Lower them into the water and bring the water to a soft boil (this usually means turning the heat down a tiny bit and cracking the lid off, you don’t want a rolling boil or your jars will knock around).  Process for 1 hour and 25 minutes (85 minutes).  Use this chart to adjust for altitude. Do not adjust the process time without consulting the chart, this is a standard chart as issued by USDA in accordance with safe preserving methods.  NOTA BENE: it is my experience that this recipe will make more than 7 jars, which is the number of jars you can fit in a standard caner. You have two options: either start two baths at once, or do it in two batches.  If you do it in two batches, your jars will have cooled significantly after 85 minutes of wait time.  You must dump out your water and start the jars in cool water. If you do not, your jars will crack. After 85 minutes at a steady boil, turn the heat off and remove the jars from the water, using your canning tongs, and place them on a wooden cutting board or towel.  Do not place them on a cold hard surface or you risk cracking them (this has only happened to me once, but it was awful!)  During their time in the caner, the pulp in the juice will have separated, and the tomatoes will have floated to the top because of the air in them.  They will look funny, like this:


Don’t despair! It seems that people’s first instinct is to think water some how got into their jars. It didn’t.  This is just how it works.  Wait for the jars to cool enough to handle then tip them upside down a couple times.  The air will start to settle out of the tomatoes, and everything will normalize a little bit.  In the end, they will look like this:


Beautiful, ready to store, and waiting to be opened.


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