Sounds like a good name for a pub, doesn't it? So, this morning I got everything prepared for cooking the jam. You can (maybe) see in the photo below that the mixture produced lots of juice overnight. I assembled all the tools I thought I'd need for making and canning the jam: plenty of jars, jar-lifter, candy thermometer, strainer and spoon, skimmer and jar funnel (cooking pot not shown). It looked like about a quart of raw fruit, so I got out two pint jars and four half-pint ones.
First step is to make sure the jars and lids are sterile and hot. Jam doesn't require hot-bath canning, so I put the jars in the oven instead of in boiling water (225F). I put the lids in a small pan of simmering water. The jar rings don't need to be sterilized.
The process of cooking the jam is pretty simple: strain the juice, bring it to a boil, skim, and boil until the thermometer reads 221F / 105C. (Note to self: get a different candy thermometer - every time I use this one, I remember how hard it is to read.) When the syrup has cooked down enough, add the rhubarb, bring back to a boil, skim and cook, stirring, for 5 minutes. Ladle the jam into hot jars (this is where the jar funnel comes in handy) and put hot lids on top, then tighten down the rings to seal.
You notice I said "jars".... but this amount of rhubarb yielded exactly one pint, so I only needed one jar. I should have used two half-pint jars, but by the time I realized this, it was too late. On the other hand, the jam makes up in flavor for what it lacks in size. Wonderfully rhubarby with just a slight bite of lemon. Beautiful deep ruby color, too.