Jams on Parade, Lemon Curd, Too
In fact, all you really need to make great jam is good fruit, 30 minutes or so to stir and spoon and some very clean equipment. (When it comes to canning, cleanliness is next to godliness.)
When you’re getting your gear together, it’s best to choose jars made specifically for canning because the glass is thick and made to withstand the pressure of boiling. And always start with new lids. Wash the lids, put them in a saucepan of cold water, bring the water just to the simmer (you don’t want to boil the lids), remove from heat and keep the lids in their water bath. To process the jams, you’ll need a deep pot that’s 3 inches taller than your jars; put a rack or a triple layer of paper towels in the bottom.
If you’re going to make refrigerator jams, meaning you’re not going to process them for long-term storage, you don’t have to be as picky about the kind of jar and you don’t need standard canning lids. Just give your jars and their lids a good scrubbing, rinse them really well, put them in a pot with enough water to fill them and bring the water just to the boil; turn off the heat.
Whatever kind of jam you’re making, you’ll need a heavy casserole that holds at least 5 quarts for cooking the fruit. Put a saucer in the freezer for testing the jam and, if you’ve got them, have jar tongs at hand. (I often use silicone oven mitts.)
Jams for storage usually have about twice as much fruit as sugar, by weight. So, if you’ve got two pounds of berries, you’ll need 1 pound, or about 2 cups of sugar. When I’m making refrigerator jams, I often use less sugar and I’ll often cook the jam to a looser consistency. These are variables you can play around with.
But here’s a key point: Even though it’s tempting to make a lot of jam at once, it’s a mistake – 8 cups of fruit is about the max. Use more and you might end up having the jam overcook before it sets.
Cook the jams while stirring, stirring, stirring. Don’t walk away – at the beginning, jams have a tendency to bubble up and you need to be around to stir down the seething fruit; and at the end, they can stick and scorch, a sorry state.
When the jam looks like it’s thickening, test it: Drop a little on the cold plate, freeze the plate for 1 minute, and then poke the jam. I like to have my jam lightly set – it will set more during its 5-minute calm-down period. If you like a firmer jam, cook it until the chilled drop wrinkles when you push it gently with your fingertip. Remove the pot from the heat and let the mixture sit for 5 minutes, a hedge against having all the fruit float up to the top of the jars.
To process the jams, pour the water out of the jars and put the jars on a heatproof surface. Fill them with jam, leaving 1/2-inch of headroom, and clean the rims; seal with a lid. Put the jars back in the canning pot (keep them upright) and add enough hot water to cover them by at least 2 inches. Cover the pot, bring to the boil, then boil gently for 10 minutes. Turn off the heat and carefully – very carefully – remove the jars, keeping them upright. Let the jam cool to room temperature.
Check the lids – they should be flat or concave and they should stay that way when you press their centers. If the seal looks iffy, refrigerate the jars rather than store them.
If refrigerator jam was what you were after in the first place, fill the jars, clean the rims, seal them and then turn them upside-down on a heatproof surface. I was told to this the first time I made jam and I’ve been doing it ever since. (I’ve decided that it truly seals the jam, but I might have made this up.) When the jams reach room temperature, turn them right-side up (you might have an airspace on the bottom of the jar, but the jam will eventually work its way down and fill it) and refrigerate them.
For more on canning and another recipe, see my friend David Lebovitz’s post on apricot jam.
PS: I’m sorry I didn’t think of this earlier. Kevin West of Saving the Season has a gorgeous and really informative site that’s devoted entirely to canning. Even if you don’t can, you should visit the site for the beautiful illustrations and Kevin’s stories; if you do can, you’ll find wonderful recipes.