Nine Lessons from a Rookie Canner

canning preserving tomato Oct 20, 2021

If you would have told me when I first started growing in the community garden that one day I'd be canning my abundant harvest, how I would have laughed!

Ugh, too much work! In modern times, there's no need. Canned vegetables are cheap, safe, and abundant at the grocery store. And they taste pretty good, too!

Yet, when you have an abundant harvest, you are faced with a decision what to with it all. Preserving it is one solution, and canning is one way to preserve it. Of course, there's also freezing, drying, fermenting, and probably other ways I don't even know about. Canning is attractive because you can store your canned produce at room temperature. 

Last year, during the summer of the 2020 pandemic, I had the time to try canning. I bought a book, I bought a water bath canning kit, and I dove in. This year, 2021, is my second year of canning. I have had some success, and I'm still interested enough in it to keep trying new things.

Before I share my lessons, here's a super high level description of the water bath canning process, which is the type of canning I'm currently doing:

  1. Gather your ripe produce
  2. Prepare the produce (clean it, cut it up, cook it, mash it, etc.)
  3. Heat up the jars 
  4. Put the prepared food in the jars
  5. Put the lids on the jars and gently screw on the jar rings
  6. Submerge jars in water in the canner
  7. Boil the water (and jars) in the canner for the specified amount of time
  8. Remove the jars and let them cool
  9. Check jars that they've sealed properly
  10. Label jars and store for good eating later

And I should mention - it's called "canning," but you are really putting your produce in jars, not cans.

Here are my top 9 lessons I have learned about canning 2 years in.

Lesson 1: Canning is expensive to get started

Getting good equipment is not cheap. Borrowing equipment or buying it used can probably save you money. Fortunately, you will use your equipment year after year - it's an up-front investment, but after that, you don't have much more to buy. 

Lesson 2: There are two types of canning

I really didn't know this starting out. The two types of canning are water bath canning and pressure canning

Water bath canning is simpler and less expensive to get started. The drawback is that you cannot can just any type of food using the water bath method. The water bath method uses boiling water to sterilize and seal the jars and food. It doesn't completely sterilize, though. Foods preserved using this method must also be acidic enough to suppress all other microorganisms that survive the boiling water. Accordingly, you can only preserve certain foods using the water bath method.

Pressure canning uses a pressure-cooker type of device to super heat and apply pressure to the jars and the food. This allows the temperature to get high enough to sterilize the jars and food, regardless of the acidity. You use this method to can everything else (corn, beans, soup, etc.); in fact, commercial canning is done this way.

The drawback to pressure canning is that the equipment can get even more expensive, and you have to deal with the pressure canner. People worry that the canner is going to "explode" or something. I suppose it can happen, but if you follow the directions carefully, you won't get into trouble. 

Lesson 3: You need a. lot. of. produce. to make canning worth the work

When canning vegetables, you clean them, cut away any bad spots, chop them up, juice them or cook them and then put them in the jars for processing. It's a lot of work and it can get messy. When you put in that much work, you would like to end up with a sizable quantity of finish products. Most canning recipes call for bushels or pounds of vegetables!

When you have a lot of raw vegetables to work with at one time, you also need tools of appropriate size - like large stock pots, good knives, etc.

Your produce must be all ripe and ready to be processed at the same time. This is tricky, especially if your garden isn't very big. This year, I stuck my ripe tomatoes in bags in the freezer as they became ripe through the late summer. When I had accumulated enough ripe (frozen) tomatoes, I was ready to go. This method worked, but it took up a lot of space in the freezer.

A smaller but significant lesson I learned by this process is that it takes a long time to thaw 6 4-pound bags of frozen tomatoes. And you don't want to try to chop frozen tomatoes because your fingers quickly go numb from the cold. 

Lesson 4: Canning is a lot of work

In case I haven't mentioned it... canning is a lot of work. And it gets messy. 

The work isn't difficult, but it requires time. Plan your time accordingly. I usually reserve a whole morning or afternoon to work on a batch. 

Kitchen appliances can help here. Use your food processor, ricer, food mill, or other  appliances to help with chopping, reaming, and mashing, when possible. 

Lesson 5: Follow the directions carefully

As mentioned above, water bath canning will only work safely when the food is acidic enough. The instructions or recipes have been developed so that the acidity is enough to keep your food safe, but if you start changing ingredients or mess with proportions, you could end up with problems. 

(And by problems, I mean food poisoning.)

Do not assume that you can swap one vegetable for another in a recipe. 

It's disappointing when you put in all the work to preserve your harvest, only to have it go bad. 

Lesson 6: A glass cooktop is not ideal

I have a beautiful black glass cooktop in my kitchen. It was in the house when we bought it, and while it's sleek and modern looking, it just doesn't work well for canning. The largest heating surface is too small for my water bath canner, and I have to take off the grate over the built-in exhaust to center my water bath canner on the burner. In fact, when I bought my canner (which is basically a huge enameled pot) and started to process my  very first batch of pickles last year, I was seriously worried that the stovetop wouldn't be able to get the water inside the pot up to the rolling boil. The pot must reach a rolling boil in order to sterilize the jars. 

It does make it to rolling boil on my cooktop, thankfully, as long as I keep the lid on. It takes a long time to get the canner up to the rolling boil, too. 

I think the problem is that my canner has a slight indentation in the bottom, and the bottom doesn't contact the glass cooktop completely. Some heat is lost. 

Lesson 7: Getting all the air out of the jars is tricky

Canning recipes instruct you to remove air bubbles from the jars. It's trickier than I thought, and I've struggled with it with every batch. You can see some air bubbles through the glass jars, but more bubbles hide within the food itself. When the canning is done, I find a layer of air at the top of the food. 

Fortunately, this is a common problem, and as long as the jar seals properly, it should be OK.

Lesson 8: Wipe the rim

Wiping the rim of the jar before you put the lid on is important, and it's the step I was most likely to forget. 

A clean rim of the jar is necessary for the lid to seal correctly and keep out microorganisms. After the jars are processed in the boiling water, and while they cool down, the metal lid of the jar will get sucked slightly inward and downward. The direct contact of the edge of the lid and the rim of the jar creates the air-tight seal. If bits of food are stuck between the rim and the lid, the seal will not happen. It will let air in and spoil your food (over time). 

If this happens, you can simply put the jar in the refrigerator and use the food right away. The food is fine when this happens, but since there's no seal on that jar, eventually air and microorganisms will get in and spoil it if it's not used up. 

Lesson 9: I have more to learn

After 2 years of canning, I still enjoy the process and I'd like to do it again next year. 

It makes me feel like a chemist!

My first several canned foods have turned out well... but not like the lovely pictures in the instruction book. A layer of clear yellowish liquid formed at the bottom of my jar of chopped tomatoes! Why is that? Is it bad or dangerous?


I'm so glad we have the Internet. Canning has been done for over 100 years and certainly others have encountered this same problem. I want to understand why it happened and  what I can do to avoid the problem in the future. 

So I researched my above questions - the layer formed because when I chopped up the tomatoes, the tomatoes released an enzyme that started to break the tomatoes down, releasing that liquid. Had I cooked the tomatoes before packing the jars, the cooking heat would have deactivated that enzyme. Fortunately, this is common and it's not dangerous. You simply stir up the tomatoes when you use them to integrate the liquid with the solids. It seems to be a "rookie mistake."

Are you an experienced canner? Did you go through some of these challenges?

The whole point of canning your harvest yourself is to enjoy eating it later. I've had mixed results. Some of my disappointments were probably that the recipe is not to my taste.

I'm eager to try the tomatoes and the tomato sauce I preserved. If the flavor is much better than grocery store cans, then I know I will continue canning. Stay tuned for an update!


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