Canning Tomatoes (the basics)

As you might have guessed given my giant pile of tomatoes, my next few posts will be all about things you can do with them: roasted tomatoes, roasted tomato salsa, tomato sauce, and mixed pepper sales. But first, let’s do the basics. How do you can tomatoes?

Tomatoes are an interesting case because they straddle the line of low-acid/high-acid food. Technically a fruit, we typically think of them as vegetables. Like most other fruits, however, they are sufficiently acidic that you can can them in a water-bath…but this is where it gets tricky. The USDA recommends that you add 1 tablespoon of lemon juice per pint, just to make sure that the acid levels are high enough. They also recommend that you process them for 40 minutes, which is much longer than I like to cook my tomatoes. The 40-minute recommendation actually came as a shock to me because for years I’ve been working with instructions that say that you only need 15 minutes for a hot pack (more on that below). Apparently, the USDA updated its guidelines in 1989 to reflect growing concerns about food-borne illness. In the case of tomatoes, the biggest concern is salmonella, not botulism.

Personally, I think this is ridiculous. I have been eating 15-minute processed tomatoes my whole life, to no dire effects. Of course, the canned tomatoes that I eat were usually either grown by someone I know or purchased at a local farmer’s market—not conditions likely to breed salmonella. If you decide to go the 15-minute route, you are doing so at your own risk (I assume no liability for your canning choices). I’m just saying that you should use common sense. Wash your hands, wash your food, remove tomato skins, and don’t purchase industrial produce. If you want to be extra-cautious, you can boil your canned tomatoes for 10 minutes when you open the jars. Or you could just follow the USDA’s advice and process them for 40 minutes.

Now: my flip attitude toward the 40-minute rule is only for hot-packed tomatoes. When you can tomatoes, as when you can most fruit, you have a choice. In a cold or raw pack, you put raw fruit in jars and cover them with some sort of boiling liquid. In a hot pack, you bring the fruit to a boil with the liquid, then transfer them to the jars. If you’re using a raw pack, you need to process your tomatoes for 40 minutes. Period. I find that I get better results with a hot pack when I process in a water-bath canner. Fruit shrinks when you heat it. If you’re doing a raw pack, it shrinks in the jars, meaning that you’ll end up with a lot less fruit than you anticipated. When you hot pack, the fruit shrinks before you put it in the jars, which means that you can use fewer jars for the same amount of produce. And, of course, if you’re worried about salmonella, boiling the tomatoes before you can them should help with that.

The alternative is to process your tomatoes in a pressure cooker. This has been my choice lately, both because it uses less energy and because the heat of the pressure cooker will kill just about anything. You can also skip the lemon juice. The catch is that some people feel that the texture of the tomatoes suffer from the heat of the process. I haven’t found that to be the case, but there is an aesthetic issue. Pressure canning usually results in a significant loss of liquid. That’s what’s going on the photos pictured at the top of this post. The jars were full, with only 1/2″ headspace when I put them in the canner, but a week later, they’ve shrunk. Cold vs. hot pack doesn’t seem to make much of a difference, so I don’t bother with heating up the tomatoes first. This is a perfectly normal side-effect of pressure canning and doesn’t affect the safety of the contents, but it freaks some people out. I wouldn’t necessarily give them as gifts. If you’re comfortable with a pressure cooker, though, this is by far the easiest and fasted method.

Long story short: You’ve got 3 basic options for canning tomatoes in water:

Water-bath raw pack: 40 minutes for pints, 45 minutes for quarts, be sure to add lemon juice
Water-bath hot pack: USDA recommends same time as for raw pack. Older instructions say 15 minutes for pints, 20 minutes for quarts. Use lemon juice.
Pressure-canned, hot or raw: USDA recommends 10 minutes at 10 pounds pressure for pints or quarts. Older instructions (use at your own risk) say 0 minutes for pints, 5 minutes for quarts (“0 minutes” simply means bring it to pressure, then turn off the heat).

You’ll need to process them longer if you’re canning in tomato juice. You can find more details and instructions at the National Center for Home Food Preservation. And if all else fails and you have a big freezer, you can just toss peeled tomatoes in freezer bags and call it a day. If you have strong opinions about tomato processing times, please leave your comments below.

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19 comments to Canning Tomatoes (the basics)

  • […] 25 minutes. I cannot, for the life of me, figure out why you would need to do this. As you saw in yesterday’s post, the USDA recommends a 40-minute processing time for regular tomatoes. Why would they require twice […]

  • Yum – I am salivating and can hardly wait to try this. Your blog looks perfect.

  • How do you find the lemon juice? For years, I never added anything to my tomatoes, but this year I decided to be extra cautious and use citric acid. Yes, safety is a true concern, but flavor is extremely important. Given the time involved, I am hoping the flavor isn’t compromised.

  • dorisandjilly

    I don’t particularly care for it, which is why I prefer to pressure can my tomatoes. OTOH, many people say that pressure cooking destroys the flavor, and I’ve never found that. A friend of mine swears by the lemon juice and says you can’t taste it. I’ll be curious to hear how yours turn out!

  • Salmonella is not the food safety issue in home canned tomatoes; Clostridium botulinum is. Some new varieties of tomatoes are less acidic than traditional varieties. Canning without additional acidity (e.g., from citric acid, lemon juice or vinegar) puts consumers at risk of botulism poisoning because the pH of the canned tomatoes may not be low enough to prevent C.botulinum from growing. Proper pressure canning (not pressure cooking) using an accurate pressure guage, and adjusting for altitude as needed, will reduce the risk.

  • larry morgan

    In the late 1950′ in high school we we served by the school cooks what we called pinwheels. I was ground beef rolled up in bread dough like a pinwheel about five inches across. They served these with mashed potatoes and gravy with a veg.This was a meal to die for.The school was in cincinnati ohio.I can not find anyone around to find how to make those. Got any ideas????

  • Ok, this makes me feel better about my own pressure-canned tomato results.


    I had assumed that having so much air in the jars after meant I did something wrong, and that the final product wouldn’t last very long. So does this mean they’re okay to hang onto until winter? I’d hate to “use up” canned tomatoes while I still have piles of fresh ones coming in from the garden every day.

  • dorisandjilly

    Sarah, they should totally last. Next time, leave the lid on the pressure-canner for a long, long time before opening.

  • Thank you so such for a very informative article about the basics of canning tomatoes. Just ensure that you follow the procedure properly to avoid bacterial growth.

  • Tony

    My wife and I put up our first tomatoes last night. We made sure the liquid level was within one-half inch of the top cooked for the 40 minutes and went to bed satisfied we had followed the directions. Woke up this morning and several of the quart jars liquid level had fallen one-half to one inch. Is this a problem? If the answer is yes, how do we correct our mistake.

  • dorisandjilly

    Sorry for the delay in my response (the blog is no longer sending me notifications, for reasons I cannot fathom). This is normal. It’s called siphoning. If you looked around the base of the jars, you probably noticed a little bit of red liquid on the counter. So long as the seal is good, a little siphoning is nothing to worry about–but do use those jars first, as the product is more vulnerable to oxidation. This affects taste and texture but not safety.

  • Carolyn Snyder

    I’ve been breaking the rules for several years without a problem. I cold pack my home grown tomatoes and process the jars in boiling water for 15 min. None have ever gone bad, they hold up, keep their bright red color, and taste fresh. I’ll put fresh lemon juice in them this year.

  • PBS

    I just processed tomatoes after I boiled tomatoes chunks and their juice. I used the hot water bath and did it for 50 minutes. I also place a1/2 tsp of citric acid in the quart sized jars. The reason why I processed for 5 minutes longer is because my cook top went off for 5 min, so the canner stopped boiling for 5 min. Do you forsee any problems in this?

  • Kim

    FYI – the guidelines for raw pack are in fact to process for 80-85 minutes (pint-quart, respectively), not 40-45. Whether this is over-sensitive is up to each person – I think we are overly hyper risk averse, but then, because I give a lot of my canning away, I don’t take the risks. It’s one thing to put myself in the path of small risks, it’s another to make that call for others.


  • Jeff

    I canned some tomatoes in a water bath for 40 minutes after making sauce which included a little vinegar and wine.
    One of the jars started to leak and when I opened it it expanded spilling sauce all over the sink. It smelled OK so I put it in the fridge. My question is should I just throw this jar away? Or, is it OK to use. It seemed that air somehow got in and expanded.

  • Paula

    I made salsa last night, which contains a fair bit of vinegar, and it simmered for 2.5 hours before canning. While jarring one batch, I forgot to turn the element back on the canning water for the first 15 minutes or so, and then it didn’t get quite the full 20 minutes that (was) recommended by my Bernardin canning book. Is it OK to reboil the salsa, and rejar it this morning? The jars sealed just fine, but I don’t fully understand the bacteria issues with tomatoes.

  • Wow I only came on here because I was in the middle of pressure canning my tomatoes and wanted to double check the time at 10lbs of pressure for quart jars.

    There sure are a lot of different ideas! My method lately has been: Put quart jars filled with water in the pressure canner and start it to boil.(lids too)

    Meanwhile I blanch and peel my tomatoes. When I get enough to fill a jar I bring out a jar and dump the hot water into my blanching pot. I then fill with raw tomatoes very tightly packed in their own juice. I add 1/2t sea salt and 1/4t citric acid for flavor. Use chopstick to get bubbles out. Because they are sitting in simmering water they are keeping warm and getting hot. I think this helps with raw pack. Wipe the rims with boiling water and then vinegar. Put hot lids and the screw top on. Tight but not too tight.

    The lid goes on the pressure canner and the canner which is already boiling is vented for about 10 minutes. Put the weight on. It takes several minutes for the pressure to get up to 10 lbs. Then I process the quarts for 10 minutes at 10 lbs. The canner gets turned off and takes at least 30 minutes to cool down. Usually I notice when I take them out they are still boiling in the jar.

    All total they are in boiling or very hot water for 30-50 minutes not including the 10 minutes at 10lbs pressure. I think they are very safe and delicious with a natural balance of acid and sweetness. Pressure canning is the best.

  • amussue

    I canned tomatoes the other night. I dipped them in boiling water to get the skins off, cut them up and put in hot jars. I didnt add boiling water to the jars i had alot of liquid from the tomatoes i just put in there. put lids on and water bathed them for 45 mins. Is it ok that i didnt put boiling water in the jars? it was a cold raw pack.

  • ray

    Will my jarred fresh tomato sauce be any good after I rejarred them because I forgot to add lemon juice? I rejarred them 6 days after I originally did them(they were stored in my closet). Thanks.