Updated: Nov 8, 2020
Jam is one of the hardest preserves to make - because it relies on a chemical reaction to get a set - it's basically a science! This article will show you just what goes into the making of jam.
There are three main foundations to making a Jam and getting it to set - unset jam can have the consistency of a soda syrup or the contents of a sliceable can of jello! These crucial foundations include: heat, sugar and acidity. Getting the level of these elements wrong can see you adding your tears to the mix.
The key component to jam making requires the formation of a molecular web that holds it all together, this is known as "Pectin", and the three main foundations help in the formation to set your jam.
Let's take a closer look at these elements:
Pectin - Is a long chain of carbohydrates known as polysaccharides. Found in plants and flowers alike, it gives structure. It is also found in the skins of fruit - these are natural levels. You can also add commercial pectin powder which is found in the supermarkets.
When you cook fruit into a jam, this structure of pectin is ruptured and the fluids will leak, this helps create that molecular web to form the jam. Pectin interacts with water during this process and produces a negative charge - this is where acidity comes in, it plays a vital role at neutralizing the negative charge of pectin.
Acidity - Lemon, or other citrus, is used to neutralize the negative charges of pectin and lowers the pH of the jam for optimal gelation - not just for the taste! Lemon juice is also added for food safety reasons, including safe canning (the process of sealing the jams, using a hot water bath canner).
By bringing the pH level down when making your jam, you greatly reduce the risk of any bacterial growth, known as botulism. It also helps the jams last longer.
Sugar - Generally speaking, in terms of traditional jam making, sugar levels are also key in getting a good set - unless you plan on reducing your sugar levels, in which case you can - this is where specialty pectin powder comes in, with the added combination of food-grade calcium - extra sugar is not required as it is with regular pectin powder in order to set, as the pectin needs calcium to set, and not sugar.
Heat - When it comes to the correct level of heat, jam typically sets at a temperature of about 104-105 degrees celsius. You don't want to burn or overcook your jam, but if you take too long in reaching this setting point, you might just render your pectin inactive! If you don't get it right, you could ruin your jam.
In summary: There are a few crucial factors that impact the setting of a jam, and many reasons why it might not set - from overcooking, or the crystallization of the sugar, to incorrect levels of pectin, heat or acidity.