Hull and slice strawberries into 1/4-inch pieces, then trim rhubarb and cut into 1/2-inch chunks—keeping them uniform ensures even cooking and a consistent texture. While preparing fruit, place your jars and lids in a boiling water bath canner and simmer the lids in a separate pan to sterilize them (this kills any bacteria and ensures proper sealing). I find that having everything sterilized before you start cooking prevents any last-minute rushing when the jam is ready to jar.

Add the sliced strawberries and rhubarb chunks to a large stainless steel pot or jam pan, then stir in the lemon juice, vanilla, calcium water, cinnamon, and fresh grated ginger. The lemon juice provides acidity to balance the sweetness and aids pectin activation, while the spices and vanilla add depth and complexity to the flavor profile. Let this mixture sit for a few minutes to allow the flavors to begin melding before heating.

In a small bowl, thoroughly whisk together the allulose and pectin, breaking up any clumps to ensure the pectin disperses evenly throughout the sugar substitute. This prevents the pectin from clumping when added to the hot fruit and guarantees smooth gel formation. I always take an extra 30 seconds here to really work out the lumps—it makes a noticeable difference in the final texture.

Heat the fruit mixture on medium heat, stirring occasionally and mashing as it cooks to reach your desired texture (leave it chunky or mash it smooth—your preference). Continue heating until the mixture comes to a rolling boil that can't be stirred down. Once boiling, immediately add the pectin-allulose mixture from Step 3, stirring vigorously for 1-2 minutes to fully dissolve the pectin and activate the gel-setting process. Then boil for exactly 1 minute more and remove from heat—over-cooking breaks down the pectin and prevents proper setting.

Working quickly while the jam is still hot, remove the sterilized jars from the water bath using a jar lifter and carefully fill each jar with jam, leaving exactly 1/4 inch of headspace at the top (this allows room for the lid to seal properly without jam leaking). Wipe the rim of each jar clean with a damp cloth to remove any sticky residue, then place a hot sterilized lid on top and screw on the ring until fingertip-tight (snug but not forcefully tight). Return the filled jars to the boiling water bath canner, ensuring they're covered by at least 1-2 inches of water.

Bring the water bath back to a rolling boil and process the jars for 10 minutes (add 1 minute for every 1,000 feet of altitude if you're above sea level). After the processing time is complete, carefully remove the jars using a jar lifter and place them on a clean kitchen towel to cool undisturbed for 24 hours at room temperature. As they cool, you'll hear the satisfying 'ping' of the lids sealing—this means the jam is properly preserved.

After 24 hours, check each jar's seal by pressing the center of the lid—it should be flat and not flex. Any jars that don't seal properly can be refrigerated and used within 3 weeks, or you can reprocess them by returning them to the boiling water bath for 10 minutes with a fresh lid. Sealed jars can be stored in a cool, dark pantry for up to 1 year.