Classic Strawberry Jam

1. Fill a large stock pot or canning pot 2/3 full with water; place a rack of some sort in the bottom and place over medium-high heat. Wash/sterilize your jars and submerge in water bath as it heats. The pot should be just about boiling by the time the jam is ready to go. Keep jars in hot (not boiling) water until ready to use. This recipe can also be stored in the fridge or freezer if you don't want to deal with canning it.
2. Place a plate or a few spoons in the freezer before you begin if you want to test the set of your jam before transferring to jars (a must for old-fashioned jam, optional for the other varieties).
3. To prepare fruit, core and coarsely chop berries, then mash with a potato masher. You should have 3 cups of mashed berries. You can also opt to run the strawberries through a food mill if you like, just know your final jam will be smoother and looser.
4. Pour mashed strawberries into a large, heavy saucepan, along with lemon juice.

For Old-Fashioned Jam:

1. Cook strawberries, sugar, and lemon juice in a heavy-bottomed saucepan set over medium-high heat, stirring occasionally to prevent scalding. Add butter if desired to reduce foam.
2. Cook, stirring occasionally, until jam reaches 220 degrees F (subtract 2ºF for every 1000 feet of elevation). Depending on the size/thickness of your pan, this will take about 35 to 45 minutes; the jam will fall off the spatula in wide, thick drips. To test the gel another way, place a dollop on a pre-chilled plate and freeze for 1 minute, then push your finger through the dollop: it should wrinkle up in front of your finger and leave a clean trail behind it. If it's not quite set, cook for another minute or two and then test again.

For Regular Pectin Jam:

1. Whisk pectin into saucepan with strawberries and lemon juice. Add butter if desired to reduce foam.
2. Bring to a full rolling boil, stirring occasionally, then whisk in sugar all at once, stirring continuously until mixture returns to a full rolling boil. Boil hard for exactly 1 minute, then remove from heat.

For Low-Sugar Pectin Jam:

1. In a bowl, whisk pectin with granulated sugar until evenly incorporated and set aside.
2. Add calcium water to saucepan with mashed strawberries and lemon juice. Add butter if desired to reduce foam. Bring to a full rolling boil, then whisk in sugar/pectin mixture, stirring continuously until mixture returns to a full rolling boil, then remove from heat.

Processing:

1. Ladle jam into hot jars, leaving 1/4-inch of head space. Wipe jar rims and screw on lids. Process in boiling water for 10 minutes, then transfer to a wire rack to cool completely. Check seals. Any unsealed jars should be refrigerated and used within 3 weeks.