Blueberry compote with no added sugar

1. Clean about 5 canning jars of no more than 470 ml and keep hot. Prepare suitable new canning lids and screw bands according to the manufacturer. Set up a deep pot with a rack and lid; preheat the water bath to about 60 °C.
2. Use only sound, ripe berries. Wash gently in small batches, drain and remove stems. Discard mouldy or spoiled berries. Bring the filling water to a boil.
3. First put about 120 ml boiling water into each hot jar. Add whole raw berries, gently shaking while filling to help them settle. Do not crush. Cover with boiling water, leaving 13 mm headspace; boil extra water if needed.
4. Release air bubbles with a suitable non-metallic tool and adjust the liquid level and headspace. Clean jar rims, apply lids and tighten screw bands according to the manufacturer.
5. Place jars on the rack in the preheated water bath, with water 25–50 mm above the lids. Cover and bring to a rolling boil before starting the time: 15 minutes at elevations up to 300 m, 20 minutes above 300 up to 1800 m, or 25 minutes above 1800 m. Maintain the boil throughout; if interrupted, return to a boil and restart the full processing time.
6. Turn off the heat, remove the pot lid and wait 5 minutes. Lift jars upright and cool undisturbed for 12–24 hours. Do not retighten or invert. Check seals, remove screw bands and date the jars. Immediately refrigerate correctly processed, freshly cooled jars that did not seal and use within 48 hours. Store only properly sealed jars as pantry food.