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Canning 101: How to Ensure That Your Jam Sets

temperature test

One of the trickiest things about making jam is achieving the set sweet spot. Cook it too long and you worry about the integrity of your cutlery as you reach in for a spoonful. Cut the stove time short and when it comes time to eat, the jam threatens to run off your toast in sticky rivulets (do know that jam this consistency is still amazing on pancakes or in yogurt. Call it a rustic syrup or old fashioned preserves and your friends will still be wowed).

plate test

First off, know that even the most experience jam maker has an off day here and there. The same recipe can yield a perfect set on Saturday and make an unfortunately sloshy batch on Sunday. Jam is influenced by the width of the pot you use to cook it, the ratio of sugar to water in the fruit, the amount of pectin in the fruit (as well as whether you add additional pectin), the elevation at which you’re cooking and even the amount of humidity in the air.

Here are a few things to keep in mind as you prepare to make a batch of jam…

  • As I mentioned above, the width of your pot can influence the set of your jam. Always choose the widest pot you have at your disposal that also has enough height to let the jam boil vigorously. More surface area means faster evaporation and ample height means you can crank the heat and let it boil. Getting the water evaporated out of your cooking jam at a speedy clip is integral to having a nice, spreadably sticky jam.
  • Take the jam’s temperature. Jam making is much like candy making in that you’re applying enough heat to the fruit and sugar to raise the temperature over the boiling point of 212 degrees and alter the structure of the sugar. The jam reaches its ideal set point at 220 degrees, so keep careful watch. Know that if you reduce the amount of sugar in your recipe too drastically, you may not be able to get your cooking jam up to the set point.
  • Before you take the jam off the heat, try the plate test. At the beginning of cooking (or even before) stash a couple saucers or sandwich plates in your freezer. When you believe the jam is cooked, grab one of the plates and plop a small spoonful at the center. Let it sit for a minute or two and then gently prod the puddle of jam with your finger. If it’s formed a surface skin and seems to be developing a certain solidity, it is done. If it is runny and saucy, give it a few more minutes.
  • Another test is the sheet test. Here, you stir a spoon through your jam and the remove it from the pot. Holding it over the cooking jam, watch as the remnants on the spoon drip back down. Do they fall back in runny drips, like rain on a window? If so, it’s not quite done. However, if they seem thick and run together in more of a sheet, your jam is finished.
  • Cooking times are estimates. When the recipe gives an amount of time for you to let the jam cook, know that that is only an approximate time. The recipe writer doesn’t know how hot your stove cooks, whether you’re in arid New Mexico verses sticky Philadelphia or what size pot you’re cooking the jam in. Use your judgment.
  • Additional pectin can help improve set, but it isn’t always a panacea. I’ve had jams that included additional pectin end up runny and then made others with no additional pectin that have firmed right up. Additionally, I’ve found recently that my beloved Certo liquid pectin isn’t working as well this year as it did in years past. I don’t know if they’ve changed the formula, but it’s thrown me off and made me remind myself of the basics of set all over again.

What are you tips for making sure your jam sets well?

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