Wash jars, lids, and screw bands in hot, soapy water, then rinse well. Dry screw bands. Put jars on a rack in canner or deep pot and add enough water to cover by 2 inches. Put tongs and ladle into pot, making sure lower 5 inches of tools are submerged in the water. Bring to a boil and boil for 10 minutes. Remove from heat, leaving jars in water. In a small saucepan, heat lids in water to cover by 2 inches until thermometer registers 180° (do not let boil). Remove from heat, leaving lids in water. Keep the jars and lids submerged in hot water, covered, until ready to use.

 

In a large bowl, whisk together sugar and pectin. In a second bowl, combine raspberries and lemon juice; mash together with a potato masher or the tines of a fork. Transfer raspberry mixture to a large, heavy bottomed saucepan and, over medium-high heat, bring to a boil, stirring frequently. Add sugar mixture in four batches, stirring 30 seconds between each addition. Return to a boil, stirring constantly, then cook 1 minute more. Remove from heat. 

 

Drain jars upside down on a clean kitchen towel 1 minute, then invert. Ladle jam into jars, leaving ¼ inch of space at top. Wipe off rims of filled jars with a clean damp kitchen towel, then top with lids and screw on “finger tight” (just screwed on with your fingertips, not cranked tight with your palm). Put sealed jars on rack in canner or pot and add enough water to cover by 2 inches. Bring to a boil, covered, then boil 10 minutes. With tongs, transfer jars to a towel-lined surface to cool. Jars will seal; if you hear a ping, it signals that vacuum formed at the top of cooling preserves has made lid concave (some jars make the sound after you remove them from water, and others in same batch may take a few hours); the important thing is for jars to eventually have concave lids. Preserves will thicken as they cool.

 

After jars have cooled 12 to 24 hours, press center of each lid to check that it’s concave, then remove screw band and lift jar by lid with your fingertips. If lid stays put, it has a good seal. Replace screw band. Put any jars that are not filled up to a 1/4 inch from top, or any that haven’t sealed properly, in the refrigerator and use them first.

 

NOTES:  Jam keeps in sealed jars in a cool dark place 5 to 6 months. Add 1 minute of processing time (both to sterilization and final processing) for every 1,000 feet above sea level.