Wash the grapefruit thoroughly then dry well. With a citrus zester, remove the colored zest (avoiding the white pith) from 5 of the grapefruits and place in a bowl or medium size measuring cup (at least 2 cups).

Cut each grapefruit in half across its equator. With a small sharp knife (a serrated knife works great), cut around the perimeter of each half where the fruit and rind meet. Point your knife slightly toward the center of the grapefruit to make up for the curve as you cut.

Then, starting at the center, slice on both sides of the thin membranes that separate the sections of fruit to free up the segments. With a small spoon remove the segments to the bowl with the zest.

After the fruit has been removed from each grapefruit half, squeeze the remaining juice into the bowl with the zest and fruit segments. Continue until you have 2 cups of the zest/fruit/juice mixture. If you end up with more than 2 cups, reserve the extra for another use.

Transfer the fruit mixture to a large pot (6-8 quarts) and add the pectin and butter. Stir to combine then bring the mixture to a full rolling boil.

Add the sugar and stir to combine. Return to a full rolling boil and boil for exactly one minute. Use a timer…it’s important to be exact. Remove from heat and allow the boiling to settle down. Remove any foam from the top surface with a spoon.

Ladle into the prepared sanitized jars, filling to within a half-inch of the top. Wipe the rims and thread, and then screw on the lids tightly.

For the hot water bath method, proceed as directed in this link).

Allow the marmalade to sit for 24 hours at room temperature, then refrigerate or freeze.