Jam Math, and a Recipe (Cherry-Berry Ginger Jam) July 31, 2012

Filed under: Food — VisibleBlue @ 1:28 pm
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A year or so ago, my mother-in-law gave me a bunch of canning jars and a canner that someone was trying to get rid of.  I found a new home for them on an empty shelf in my basement, and they’ve been there ever since. After all, I have a freezer, right? Can’t I just store everything in there?

Well, after a nasty weekend-plus-long power outage and a summer full of tasty berries from my CSA, I see the value in canning. I bought a few lids and gave myself a crash course in canning by cobbling together little tips I found all over the internet. One thing I noticed over and over again was the warning not to alter a jam recipe, or it won’t set. But that’s not my style! If I can’t personalize and experiment with my cooking, I’m just not interested.

Homemade Zesty Dill PicklesFeeling daunted, I started small with this Zesty Dill Pickle recipe I found. Technically, it doesn’t involve canning at all, but I did get to use the jars and lids. I haven’t tried them yet as they take a few weeks to pickle, but the brine smelled fantastic. (As fantastic as something that’s half vinegar can smell, anyway.) I did one batch of cucumbers and peppers and another of green beans.

After that, I decided to go ahead with the jam. Worst case scenario – a learning experience and lots of runny ice cream topping, that doesn’t sound so bad! I didn’t have a recipe to go off of specific to the fruit I had on hand, so I tried using a little math to find the sugar to fruit ratios myself.

First on the list of fruit that had to go – blueberries. After crushing them, I had about 2 cups of fruit, which was about 40% of the fruit required for the blueberry jam chart in the pectin box. 40% of the sugar in that recipe was 1.6c, so I wrote that number down and went on. I also had about 2 cups of crushed blackberries and raspberries, a little over 30% of the fruit called for in the raspberry jam chart. 30% of the sugar was 1.38c. At this point, I had 70% of the fruit accounted for, so I filled the last 30% with sweet cherries. 30% was 1.5c of cherries and .9c of sugar. Adding the sugar totals together produced about 3.88c of sugar, so I just rounded it to 4 cups even. I used grated fresh ginger as well as ground ginger to add a little more depth to the flavor, and a bit of lemon juice and zest.

At this point, I followed the directions in the box of pectin. (You can find those here if you need more detailed directions.) The process wasn’t difficult, just time consuming. The jam turned out great, but maybe a little sweet. It had a fairly firm set so I’m sure you could reduce the sugar by at least 1/4c, if not more, or use sour cherries instead. The ginger adds a nice bite to counteract some of the sweetness. This recipe made about 7.5 cups, so there’s a half-jar in my fridge that we’ve been enjoying!


  • 1 pint blackberriesCherry-Berry Ginger Jam
  • 1 pint raspberries (crush with blackberries to make 2 cups total)
  • 1 quart blueberries (crush to make 2 cups)
  • 2.5 cups sweet cherries (chopped in food processor to make 1.5c)
  • 4 cups sugar, divided
  • 1 box less/no sugar needed pectin
  • 1 inch grated fresh ginger
  • 1/2 tsp. ground ginger
  • half a small lemon, zested, plus a generous squeeze of juice

Combine crushed fruit, 1/4 cup sugar, and pectin in a large saucepot. Bring to a full boil over high heat, stirring constantly. Stir in remaining sugar, return to a full rolling boil, and boil exactly one minute. Remove from heat and skim foam if desired. Fill prepared jars to within 1/8 inch of the top, wipe the rims, and cover with two piece lids. Process in a boiling water canner for 10 minutes (at sea level.) Let stand 24 hours at room temperature.

I’m thrilled that the experiment worked out – here is the formula I used to arrive at this recipe, in a little clearer format than the rambling words above. The reason I needed to use the formula was because I wanted to make a full batch of jam with the whole box of pectin, but I didn’t have enough of any one fruit. This method requires that each original recipe uses the same amount and type of pectin (if any) as they are not interchangeable. I can’t guarantee it’ll work for every recipe, but it seemed to do the trick in this case! Sorry if this is unclear – as you can see, math is not my strong suit. Feel free to leave a comment with any questions and I’ll do my best to explain any confusing areas!  (Example in red.)

fruit on hand (crushed) / total fruit in original recipe = percentage of fruit 
--- do this for each fruit, until the percentages add up to 100%
2 cups raspberries (crushed) / 5 cups berries in original recipe = 0.4, or 40%; 
2 cups blueberries (crushed) / 6.5 cups berries in recipe = 0.31, or about 30%;
1.5 cups cherries (chopped) / 5 cups in recipe = 0.3, or 30%

sugar in original recipe * percentage of fruit = new sugar amount 
--- again, do this for each fruit you're using
raspberries: 4 cups sugar * 0.4 = 1.6 cups sugar;
blueberries: 4.5 cups sugar * 0.3 = 1.35 cups sugar;
cherries: 3 cups sugar * 0.3 = 0.9 cups sugar;

fruit 1 new sugar amount + fruit 2 new sugar amount + ... = total sugar
1.6 c (rasp) + 1.35 c (blue) + 0.9 c (cherries) = 3.85 c sugar total (I rounded up to 4)


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