Taste and feel as you go. It sounds simple – and it is. When it comes down to how much sugar you need, two apples can be very different, as can rhubarb harvested early or late in the season, so always be sure to use your taste buds to tell when the balance is just right.
Consistency. You can choose to use a gelling agent to make your jam set and the end thickness should depend on your personal taste. Another way to thicken your jam is to extend the cooking time. Keep a watchful eye and experiment. You can’t know how a jam will set until it has cooled. One trick is to put a couple of spoons in the freezer before starting the cooling process. Put a dollop of jam on the ice-cold spoon and it will cool down quickly, giving you an idea of how the final result will be.
Sterilization. Most people use a sodium benzoate mixture to sterilize jars. However, some people are sensitive to it, so use it with caution. While it is a matter of taste, an alternative is to sterilize jars using cheap vodka, as this will also kill bacteria. In general, sugar helps preserve the fruit, but if the mixture comes into contact with a “dirty” jar, then bacteria will form much faster.
Place your jars in the kitchen sink and the lids and rubber seals in a bowl. Pour a little sodium benzoate in the jars and fill with boiling water – doing the same with the bowl of lids. Wait to empty the jars until you are ready to fill them with jam. If you make a huge portion, you can also add a bit of sodium benzoate to the jam as a preservative. If you do add a preservative, do so after the jam has stopped boiling, as the preservative will lose its potency otherwise.
Filling. When making jam, put the lid on tight right away. This will create a vacuum seal. Also make sure to pour the jam into the jar as soon as it stops boiling. Don’t open the jar until you’re ready to eat it. Conversely, if you’re making jelly, wait until the mixture has cooled before putting the lid on.
Storing. Store your jam in a dark and cool place. It’s a good idea to use smaller jars that can be used up more quickly. Large jars can be difficult to empty before they turn bad, even though jam does have a long shelf life.
Learn by doing. Always sterilize an extra jar in the event that you have jam left over. It’s easier to sterilize an extra jar at the same time as the others rather than having to sterilize one at the last minute.
Shelf life. There are a lot of different indicators for when jam has gone bad. The most obvious is mold. If there is the slightest indication of mold in your jam, it must be discarded. This also applies if the jam begins to taste fermented. That is not a good sign. But you can expect a long shelf life as long as you take care to sterilize the jars, store them in the dark and don’t open them all of the time.