The Pomona pectin box contains recipes and measurements suitable for substituting regular pectin to the Pomona type. Suggest that if you do not have the Pomona yet, go to their web site and it will offer several recipes. Pomona is pretty much fool proof and if used incorrectly, like adding way too much, you can end up wth stiff rubber like jellies. The nice thing is you can make triple batches or more, without worring about if it will set up or not, unlike regular pectins. It requires a calcium additive to set. The calcium is in a tiny packet that is included and is mixed with a little water. They give you plenty of the calcium, so if I make a 30 cup batch, I use the whole calcium packet. The Pomona works best if you use a blender to dissolve it in some juice or water. Usually, I do that and it looks like a liquid pectin. I pour it out of the blender into a bowl so its easier to pour it into the boiling mixture. The final item added is the calcium water, and then you just ladle it into jars, cap, and process in a BWB. With the very sour rhubarb, I would not go any lower in sugar, but you can do without it and use an artificial sweetener that you like instead. Converting requires only to know how much Pomona compared to regular Pectin. Its amount can vary greatly, depending on the batch size.

I would try a sample batch first to figure out how much sugar per cup of fruit will be of a good sweetness for you, and to make sure the amount of pectin is right. They recommend 1/2- 3/4 tsp. pectin per cup of fruit; I would err on the side of 1/2 tsp per cup. Ken is right, it is a bit rubbery if you overdo the pectin, and you sure don't want to be stuck with 12+ cups of rubbery, overly tart jam!

1 c. crushed blueberries
1/2 c. rhubarb
a pinch- 1/4 tsp lemon zest
1 tsp. lemon juice
1/3 c. sugar
3/4 tsp. Pomona pectin powder
1 1/2 tsp Pomona calcium water

In a pan, mix together the berries, lemon zest and juice, and calcium water. In a small bowl, mix together the sugar and pectin powder; mix well. Bring the juices in pan to a boil; whisk in the pectin/sugar mixture, stirring well to dissolve. You might check the sweetness at this point and if the rhubarb has it too tart, mix in a little more sugar, or honey, or Splenda, or whatever. Return to boil and remove from heat.

When it cools off, you'll be able to see whether it's thick enough for you or not, and can adjust the amount of pectin accordingly when you do your big batch.

When I do low sugar (as opposed to sugar-free), I never have a problem getting the pectin to dissolve when mixed in first with the sugar and then added to the berries. I only use the blender method Ken talks about when I'm doing a no-sugar jam.