Chop rhubarb into 2.5 cm slices.

Combine rhubarb and water in a large stainless steel saucepan.

Bring to a boil over high heat.

Simmer for 5 minutes, then remove from heat.

Pour mixture through a cheesecloth-lined strainer.

Tie rhubarb pulp in cheesecloth to form a bag.

Hang the rhubarb pulp bag to drip overnight (approximately 10 hours).

Clean jars, lids, and rings in hot, soapy water.

Place jars in a canning kettle and bring to a boil.

Put lids and rings in a bowl of very hot water.

Measure the rhubarb juice; you should have 850 mL. Add water if needed to reach the desired amount.

Combine juice and sugar in a large stainless steel saucepan, mixing well.

Add butter to reduce foaming.

Bring juice and sugar to a full rolling boil over high heat.

Add liquid pectin, squeezing the pouches completely.

Continue to boil for 1 full minute, then remove from heat.

Skim foam from the jelly.

Pour jelly into 250 mL jars, leaving 1 cm of headspace.

Wipe jar tops if necessary.

Seal with lids and tighten rings fingertip tight.

Bring canning kettle back to a boil and process for 10 minutes.

Remove jars from water and place on a towel to stand for 24 hours before enjoying.