Tomatoes are an interesting case because they straddle the [...]]]>
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.