I make jam by feel, not chemistry. Luckily I’ve read enough about chemistry -- and practiced enough -- so I have a pretty good idea about which things will work, and which things, won’t. Preserving food always contains a small risk of spoilage. But, when you’re working with fruit, especially acidic strawberries (I suggest locally grown berries, and as fresh as possible; the ones that soften the fastest are the most likely to be super delicious and more acidic, too), the risk of actual danger is almost nil. You may end up with one jar out of a few dozen that grows mold, or ferments into strawberry jamwine. Toss these in the compost. Eat the rest.

This will make a soft jam; depending on your skill and the natural pectin in the strawberries, it may be more sauce than jam. This means they’re oh-so-much better on pancakes. So get flipping.

Steps

1. Rinse, hull, and slice your strawberries. Halve them if you like a chunky jam; chop into bits if you like more of a smooth jam.
2. In a large bowl, mix strawberries with honey and the calcium water, if you’re doing Pomona (a tablespoon or so).
3. Using a paring knife, disengage several bits of the lemon peel, leaving the pith behind. These should be roughly (very roughly) 1” square; big enough, anyway, that you can pick them out later if you like. Toss into your bowl.
4. Slice the vanilla bean lengthwise, and crosswise. Toss the pieces in.
5. Squeeze in the lemon juice left in the half-lemon.
6. Now, you decide: are you in a hurry? If so, skip to the next step. If not, stir your strawberry mixture together and put a towel over it. Refrigerate overnight, or until you’re ready to jam.
7. Pour strawberry mixture into a large, wide pot. Bring to simmer over medium heat; stir in the half-box of pectin powder.
8. Adjust heat to keep mixture at a low simmer, mashing berries with a French rolling pin or potato masher to your liking.
9. Depending on the pectin you used, you’ll get a lot of foam. The foam is delicious! If you’d like, skim it off. I suggest leaving it on a nice wide plate, and tasting prodigiously once it’s cooled. If you used a lot of pectin, it may harden into fruit leather overnight.
10. Cook anywhere between 20 minutes and a few hours at a low simmer, stirring and mashing (to your liking) frequently.
11. Meanwhile, rinse your jars and lids in hot water. This should make about two pints; I like to use half-pint jars.
12. Prepare a water bath (a nice, thick-bottomed pot that will hold your jars with a little room above them to be completely covered with water -- filled half-way with water). Bring barely to a simmer (180 degrees is hot enough, if you have a thermometer).
13. Taste your jam. (Careful, don’t burn your tongue.) Is it sweet enough? If not, add more honey. Give it a good stir and taste again.
14. Using a wide-mouth funnel and a ladle, scoop jam into jars. Leave about ½ inch space between the top of the jam and the mouth of the jar. Too much, or too little, and you’ll end up with failed seals.
15. Wipe the rims of the jars with a damp towel and set on the lids, screwing the rings on tight. Lower into the water bath.
16. Process (i.e. keep jars in the hot water, between 180 degrees and boiling) for 25 minutes for half-pints, and 30 minutes for pints.
17. Lift jars out and set on counter.
18. Check seal after 24 hours (or so) by unscrewing the rings and pulling up tight on the lids with your fingertips. If it doesn’t come off, success! You’ve safely preserved some delicious jam.