Juice your lemons: Start by juicing enough lemons to get around 12 cups of juice. Pour it into a large bowl or pitcher with a spout.
Prep for canning (if needed): If you plan to can the concentrate, get your jars, lids, and water bath canner ready now.
Make the syrup: In a large saucepan over medium heat, combine the lemon juice and sugar. Stir gently for about 10 minutes until the sugar is completely dissolved. Don’t let it boil. The syrup should reach about 190°F.
Cool and store: Let the syrup cool slightly. Pour into airtight containers and store in the fridge for up to 3 weeks — or continue to can it for longer storage.
Sterilize your jars: While the syrup cools, sterilize your canning jars in a boiling water bath. Warm your lids in a small saucepan over medium heat.
Fill the jars: Ladle the hot (not boiling) syrup into your warm jars, leaving ¼ inch headspace. Wipe the rims, add lids, and screw on rings until fingertip-tight.
Process in a water bath: Place jars in the canner, making sure they’re covered by 1–2 inches of water. Process for 10 minutes (under 1,000 ft elevation).
Cool and check seals: Remove jars and place upright on a towel. Let them cool completely. Once cool, press the center of each lid — if it flexes, refrigerate that jar and use it first.
Store: Remove the rings and double-check your seals. Store sealed jars in a cool, dark place for up to 6 months.