What I did on my summer vacation: made Rhubarb and Whole Strawberry Jam from Christine Ferber's "Mes Confitures".
The farmer's market still had some young rhubarb, and strawberries are peak season in Washington now, so I decided to make some more jam. This is the second recipe I've made from Ferber's book; the first was plain rhubarb jam (blogged here). Ferber's jams are very sweet (to my taste). She prescribes a ratio of 80% sugar (to fruit, by weight). I decided to modify this batch of jam to 60% sugar. I also cut the recipe approximately in half, which resulted in four half pints, plus about 2/3 cup extra.
600 gm prepared rhubarb (trimmed, stalks cut lengthwise, diced)
360 gm sugar
600 gm strawberries (washed and hulled, left whole)
360 gm sugar
juice of one lemon
The directions for cooking the jam are a bit complicated at first reading. Basically you are making each fruit into jam separately, and combining them at the end just before canning. The whole process takes three days. I had to write out a schedule to keep track of all the steps. I found several internet sources discussing the recipe and telling about modifications, which was a big help, and based on their suggestions, I cut back on the most complicated step, which calls for bring the strawberry mixture to a boil 5 times, repeating the sequence four times at 8-hour intervals. EH? The idea is to concentrate the syrup and infuse the whole berries with syrup without mashing them. I cut the interval time down so that I could get this done in one day. I also changed the final boiling step so that I cooked the two fruits together, rather than cooking separately, combining, and cooking again. My process was:
Mix strawberries, sugar, and half the lemon juice in a non-reactive bowl, cover and refrigerate overnight.
Strain the berry syrup, bring to a boil and boil for 5 minutes, pour the syrup over the berries, skim, cover, refrigerate.
Mix the rhubarb, sugar and the rest of the lemon juice in a non-reactive bowl, cover and refrigerate overnight.
In the morning, put the strawberry mixture into a pan and bring it to a boil 5 times (bring to boil, take off heat until boiling stops, return to heat and bring to boil, and so on). Wait 2 hours and repeat. Do the 5 times boiling four times in total.
Get your canning jars and lids sterilized: lids in a pan of simmering water, clean jars in the oven at 225F.
Then take the rhubarb mixture out of the fridge. Strain the juice of both mixtures into a pan. Bring to a boil, skim and continue to cook at a boil until the syrup reaches 221F (105C). Add the fruit; continue to boil, skimming any foam, for 5 minutes.
Fill the jars to the top, wipe the rims if needed. Put on lids and screw down the caps, then turn the jars over to cool. Alternatively, you can water-bath process them (see here for instructions). The "turn jars over" method is the traditional French method.
A note on sugar: in the rhubarb jam I made earlier, I used unbleached sugar, and the resulting jam turned out a bit on the brownish side of red. For this jam I used white sugar, and the color is much better. The jam is very tasty, tart and sweet. I think if I make this again, I'll use a higher proportion of strawberries to rhubarb, perhaps 60/40.