Although it’s surprisingly easy to can tomatoes, it’s also a kitchen task with a few hard-and-fast safety rules. I grew up canning, learning from the women in my family, and have taught canning classes for five years. Here are questions that my students ask most often:
What varieties of tomato are best for canning? For paste? For jams or chutneys? What is the expected yield?
Although just about any tomato can be canned, Brandywines are consistently exceptional. They are meaty, large, not too seedy or full of watery pulp, and a very pretty red. They are also widely available and reasonably priced compared with many heirloom varieties.
Always choose disease-free tomatoes. If you cut them open and they are black inside, that is a sign of blight, and those tomatoes should not be processed. Overripe tomatoes, often marked as “seconds” at farm markets or farm stands, are wonderful for canning. Just make sure to cut out any bad spots during prep.
Romas, San Marzanos or other “paste type” tomatoes are best for, well, paste. Frankly, paste may be the least rewarding tomato product to put up, because 20 pounds of tomatoes yields only two or three cups of paste.
Any tomato can make a superb jam or chutney. The more watery the tomato, the longer the cooking time. Consider the color of the tomato when making these long-cooked products. Yellow tomatoes or green (ripe) tomatoes do not cook down to an attractive color; try the dark ruby, carmine or purplish types for a gorgeous end product.
Expect two to three pounds of raw tomatoes to convert to one quart of crushed tomatoes. For tomato sauce, plan on four to five pounds per quart. For jam, chutney, ketchup and other long-cooking, thick preparations, it will take about eight pounds to make a quart.
Why do tomatoes have to be peeled for canning? What’s the best way to peel, seed and make sauce?
Tomato skins can be tough and bitter, so it’s nice — but not necessary — to remove them from tomatoes to be canned.
A ridiculously easy and satisfying method, presuming you have the freezer space, is to seal tomatoes inside food-safe plastic bags in the freezer. After a few hours, the skins will split and slip right off. This is particularly useful if you are growing tomatoes, as gathering sufficient weight to make canning efficient may take a few days. Holding them in the freezer will not change their taste, texture or appearance.
The more widely used method for peeling tomatoes is the one you’ll find within many Washington Post recipes: Use a sharp knife to score an “X” at the bottom of each tomato and remove the stem. Drop a few at a time into a pot of boiling water and remove them as soon as they bob to the surface. Peel off the skins as soon as the tomatoes are cool enough to handle and discard the skin. (I use a cooler filled with ice to stop the cooking and hold the tomatoes as they come out of the boiling water.)
If you are planning to make a sauce, a food mill is indispensable. There are classic stainless-steel food mills that clamp on the edge of a counter or table. Simply feed cut up tomatoes into the top, skin and seeds are ejected out the side and the sauce pours from the spout. These mills are generally available at hardware stores; used ones are often on eBay, in secondhand shops and garage sales. They make fast work of a big box of tomatoes. Even easier: the food-mill attachment for the KitchenAid stand mixer.