|Lillipilli Jelly - go HERE to see how I made it.|
Pectin: Is a complex carbohydrate found supporting the cell walls in the rind/skin and core of certain fruits.
Sugar: It has two roles, the firstly its involved in lowering the water activity of the solution (this simply means decreasing the amount of free water in the solution by making it associate with the sugar molecules). By lowering the water activity, it forces the pectin molecules to associate with each other (agglomerate) and form a matrix. The second role of sugar is that the dissolved sugar molecules are incorporated into the pectin matrix (acting to suppress the repulsion between pectin molecules forming a strong matrix)
Acid: At a low pH the hydroxyl and carboxyl side groups of the solubilised pectin molecules are charged, this encourages Hydrogen bonding between charges on different molecules. The repulsion between the molecules is over come by the high concentration of soluble sugars, allowing crosslinking and the formation of a matrix.
Have a squiz at my handy dandy infogram.
Why is choosing fruit/combinations important?
Different fruits have different Pectin contents, this is why you see combinations of berries and apple or rhubarb and orange, so that the pectin rich (apples and oranges) substitute the pectin poor (berries and rhubarb).
When the fruit ripens the pectin is broken down by enzymes (Pectinase and Pectinesterase) - this action is seen by the softening of the fruit. So if you want to use really ripe fruit - typically you will have have to substitute some extra pectin (from under ripe to ripe fruit, or from powdered pectin)
Why you can't skip the sugar.
If you are making a traditional jam or jelly you can't get away from the sugar! Typically jams/jellies using pectin extracted from fruit will need greater than 55 wt% solids.
If you add too much water to the fruit you are going to need to add more sugar to make up for it and cross your fingers the fruit had enough pectin to set- therefore Less water to start with is safer!
It also tastes yummy :)
Why Boiling is a balance.
Heat plays a very important role, firstly its needed to break down and solubilise the pectin from the fruits cell walls. Secondly, it concentrates the solution (by evaporating the water - this is why large diameter pots are commonly used) and allows the gellation to occur. BUT if you boil for too long it can taste cooked or in extreme cases the pectin molecules can hydrolyse (read break down) then it will never work unless you add more.A rule of thumb is that if the solution isn't gelling (as seen on a spoon removed from the pot) after 10 minutes you will need to add some thing...
Why fancy equipment would make troubleshooting easy peasy!
In an ideal world we would all have fancy equipment in our kitchen
pH meter - the ideal range for pH is 3.1 to 3.3 , greater than this and it won't set well - less than this and it will set tooo well and form weird chunky streaks BUT If you don't have a pH probe and you are worried you pH is too high - chuck some tartaric acid as your solution is boiling (its strong be careful 1/4 tsp at a time) and see what happens! (Adding either citric or tartaric acid straight rather than lemon juice can be easier to control and won't introduce unwanted flavours).
Refractometer - You can infer the sugar content with these babies BUT if you don't have one - if the sugar content is high enough (> 55wt%) it should be gelling and happy! (If not- chuck some more in as it boils)
If all of the proverbial hits the fan: You can always take the pot off the heat - cover it - and pop into town to buy some JamSetta (the sachets not the jam sugar). Heat the pot again and stir in the little sachet and bring to the boil again - It definitely will set now. (If it doesn't you are on your own!- or just keep adding sugar until A). It gels, or B). You have created a delicious taffy type substance.
What's with the calcium?
If you frequent fancy cooking stores, or read molecular gastronomy books (or are obsessed with low sugar jams) you may have encountered LM pectin. This is simply a pectin molecules with less methoxy groups than the pectin recovered from fruit (referred to as HM pectin). To promote gelation, rather than sugar, divalent ions are used - Most commonly calcium. The ions bridge the polymer chains, encouraging crosslinking and then agglomeration. Using such pectin is handy as less sugar is needed (MUCH LESS!) and also it sets at a much lower temperature, meaning less heat is needed.
Want to read more? This is a good reference.