I know, you might be looking at that title all skeptically, thinking “I like tomatoes, sure, but JAM? What are you even talking about?” This might be one you have to just take on trust. Tomatoes make some amazing jam. It’s great on toast, but especially tasty along with eggs and/or sausage. I think it’s the closest you can come in mid-winter to the taste of a fresh, flavorful tomato picked right off the plant. It’s not savory, but it’s not as sweet as other jams, and definitely not as tart and fruity. And if it’s your first canning experience, the acidic content (tomato plus added lemon) makes it a safer one.
There are a lot of recipes out there if you google a little, but I really like this trio. The first time I made tomato jam, I split my tomato haul into three pots (because I couldn’t pick!), and made a small batch of all three recipes. After that, I’ve only ever made the sweet & spicy.
I make it pretty much as it’s written, using regular light brown sugar, cloves, cinnamon, red wine vinegar and lime juice. If you’re having trouble imagining sweet jam with the flavor of tomatoes, note that the fruit:sugar ratio is much lower on the sugar end than other fruit jams: 455g tomatoes to 45g sugar in this recipe, or 10:1 by weight.
The other sweet-but-not-too-sweet tomato preserves that I’ve really enjoyed is the New York Times recipe for preserved tomatoes with lemon. They call for small pear-shaped tomatoes, but anything smaller than a golf ball will work just fine. And I don’t bother with peeling them anymore – just check that the tomatoes you’re using don’t have particularly thick skins. With most small tomatoes, you won’t even notice them in the preserves. The NYT recipe is interesting in that it has you put the tomatoes, sugar, and lemon slices in a saucepan overnight — with no heat, just room temperature over time. The next day, you add the spices and gently cook until the tomatoes start to go clear. You can remove them and the lemons and boil the syrup that remains, so that it thickens a bit. But the idea is to leave the tomatoes intact (which is why smaller is better). If you want to keep them throughout the winter, sterilize the jars first (leave in boiling water for 15 minutes), then fill and process according to the recipe.
“Processing” canned goods requires boiling the (nearly-full) jars, with 2-part lids (shown at right).
How full you fill your jars will depend on the food you’re canning (generally 1/8″ to 1/4″ from the top of the jar).
How long you boil the jars will also depend on the food you’re canning (10 minutes up to multiple hours).
When you’re canning acid foods (fruits, jams, and pickles, for the most part), boiling water and a large stock pot are sufficient. When you’re canning low-acid foods (vegetables and meats), you have to use a pressure cooker — a boiling water bath doesn’t get hot enough to destroy potentially harmful bacteria.
Our advice when canning is to always use a recipe that’s been tested, and follow the instructions in the USDA and Ball guides.
You don’t have to process your jam if you’re just going to store it in the refrigerator, of course. Processing is necessary for safe room-temperature storage, which gives you more time to use it (and/or more flexibility to give your canned goods as gifts to friends). But you may find it makes sense to try a recipe first — keeping the results refrigerated — and make it again w/ the processing steps added in, if you like it enough to add those steps.
The National Center for Home Food Preservation has many guides available online for free, in pdf. They’re the source for USDA standards and guidance on food safety.
The Ball Blue Book is magazine-sized, and available most places that keep a canning display (jars, lids, equipment) from Ball. For now, this means the larger stores; Common Ground and Green Top don’t carry jars and lids at this time.
Sadly, one of my favorite go-to blogs (Tigress in a Jam) for jam ideas seems to have been abandoned and taken over by advertising bots, but you can find images and recipes from the participants in her jam challenges over the years on her Flickr group.