The refrigerator test
Updated
You need
- Two or three small plates, in the freezer before you start
- A teaspoon
The steps
This is the oldest test in the craft and it is still the most useful one for jam, because it tests the thing you actually care about rather than a proxy for it. It takes five minutes and the five minutes are the whole method.
- Put the plates in the freezer before the batch goes on, not when you need them.
- Remove the pan from the heat. This matters: the batch keeps cooking while you wait.
- Pour a small amount of the boiling mixture onto a cold plate.
- Put it in the freezing compartment for a few minutes.
- Push the edge with a finger. If it wrinkles and holds, it has gelled.
Why it is the right test for jam
Temperature tells you about concentration and a refractometer tells you about dissolved solids. Neither tells you how the finished product behaves on a cold plate, which is the experience a customer has. This test skips the proxies.
Because a jam is eaten cold and this is the only test performed cold. The sheet test and the thermometer both read the hot mixture and infer; this one shows you the finished texture. On a preserve with whole fruit, where the other two are hard to read, it is the one to use.
Its cost
The cost is time at exactly the moment you have least of it, with a pan at a rolling boil and nothing else to do but wait. That is why it gets skipped, and why having the plate already in the freezer is most of the discipline. Put two in before you start the batch; the second one is for the test you have to repeat.
Time, and a stopped batch. Three or four minutes off the heat per test, and two tests is most of ten minutes. That is the reason to have the plates cold in advance and the reason not to use it as the only test on a long run.