Bring boiling-water canner, half full with water, to simmer. Wash jars and screw bands in hot soapy water; rinse with warm water. Pour boiling water over flat lids in saucepan off the heat. Let stand in hot water until ready to use. Drain well before filling.
Trim rhubarb; cut into 1-inch pieces. (Do not peel.) Put through food chopper, using finest blade. Or grind, in batches, in food processor or electric blender. Place three layers of damp cheesecloth or a jelly bag in large bowl. Pour prepared fruit into cheesecloth. Tie cheesecloth closed; hang and let drip into bowl until dripping stops. Press gently. Measure exactly 3-1/2 cups juice into a 6- or 8-qt. saucepot.
Stir sugar into juice in saucepot. Add butter to reduce foaming. Bring mixture to full rolling boil (a boil that doesn't stop bubbling when stirred) on high heat, stirring constantly. Stir in pectin. Return to full rolling boil and boil exactly 1 min., stirring constantly. Remove from heat. Skim off any foam with metal spoon.
Ladle quickly into prepared jars, filling to within 1/4 inch of tops. Wipe jar rims and threads. Cover with two-piece lids. Screw bands tightly. Place jars on elevated rack in canner. Lower rack into canner. (Water must cover jars by 1 to 2 inches. Add boiling water, if necessary.) Cover; bring water to gentle boil. Process 5 min. Remove jars and place upright on a towel to cool completely. After jars cool, check seals by pressing middles of lids with finger. (If lids spring back, lids are not sealed and refrigeration is necessary.)
How to Measure Precisely
To get exact level cup measures of sugar, spoon sugar into dry metal or plastic measuring cups, then level by scraping excess sugar from top of cup with a straight-edged knife.
At altitudes above 1,000 feet, increase processing time as indicated: 1,001 to 3,000 feet - increase processing time by 5 min.; 3,001 to 6,000 feet - increase processing time by 10 min.; 6,001 to 8,000 feet - increase processing time by 15 min.; 8,001 to 10,000 feet - increase processing time by 20 min.
Every once in a while, you may find that your jam does not set the way you expected. If your efforts resulted in a runny batch, try our Remake Directions to improve your finished jam. If your jam still doesn't set, you can always use it as a glaze or syrup.
Calories From Fat
% Daily Value*
Total Fat 0g
Saturated Fat 0g
Trans Fat 0g
Total Carbohydrates 13g
Dietary Fiber 0g
* Percent Daily Values are based on a 2,000 calorie diet.
Makes 7 (1-cup) jars or 112 servings
* Nutrition information is estimated based on the ingredients and cooking instructions as described in each recipe and is intended to be used for informational purposes only. Please note that nutrition details may vary based on methods of preparation, origin and freshness of ingredients used.