The roselle which we most commonly call ‘rosella’ in Australia is part of the hibiscus family (Hibiscus sabdariffa). It’s most useful part is the bright red, fleshy calyx which is used to make some food colourings, teas, cordial and jam. If you’ve ever seen the ‘Wild Hibiscus’ brand flowers in syrup which are popped into champagne glasses to gussy up the bubbly it’s the humble rosella calyx!
Making jam is a scientific process. If you’re thinking “Precision! Accuracy! Special equipment!” rest assured – it’s not that kind of scary science, it’s easy! Jam is the result of a chemical reaction between pectin (a carbohydrate), sugars and fruit acids.
- ½ 9L bucket of rosellas
- 3-4 cups of sugar (have more on hand because you need to have equivalent amounts of fruit pulp and sugar)
- 1 apple (peeled, cored, chopped)
- Juice of 1 lemon
- Soak the fruit in a sink full of cold water for 10 minutes and then drain. Separate the red calyx from the seedpod. Some recipes suggest you use an apple corer to do this but I think it’s just as easy to peel the calyx away by hand. Reserve the red calyx
- Place the seedpods into a saucepan, cover with water and simmer for 10-15 minutes until the seedpods are soft and translucent. This extracts the pectin from the seed pods. Remove the seed pods (use a slotted spoon or strain, reserving the liquid in a large saucepan)
- Add the red calyx, juice of one lemon and an apple (peeled, cored and chopped). Simmer gently until very soft
- Measure the quantity of fruit pulp and add cup for cup sugar to fruit (or for larger amounts 1L pulp = 1kg sugar). Stir over a gentle heat until the sugar is dissolved
- Bring to the boil. The jam will froth high in the saucepan so it needs to be no more than half full before you start boiling! Test for setting by putting a saucer in the freezer to chill, then put a teaspoon of jam on the saucer. Wait for it to cool and then push the top with your finger – if it wrinkles it’s cooked correctly
The jam should also stop frothing as it gets close to its setting point so watch for this. Using too high of a temperature or cooking for too long can destroy the pectin resulting in a poor gel (you end up making more like a thick syrup)
6. Bottle the jam into hot, clean jars and seal immediately.
Tip: For any kind of Jam making, make sure your fruit isn’t overripe – overripe fruit does not have as much pectin as an under-ripe fruit so you might have trouble getting the jam to set.
And now for the Science… HOW it all works!
The pectin in fruit (or commercial pectin if you’re using jam-making sugar) precipitates out when sugar is added making insoluble fibres. The sponge-like insoluble fibres trap fruit juice and the result is a gel.
Rosellas, apples, blackberries, cranberries, plums and quinces (to name just a few) have lots of natural pectin and thus are good for making jams. Strawberries and apriocots on the other hand are low in natural pectin and so they need to be combined with another fruit, or a commercial pectin product needs to be used to make them gel. So rosellas are a good place to start for a beginner!
Before pectin extraction…
After pectin extraction…
Sugar is necessary for the gel to form so I’m afraid you can’t skimp on sugar for the sake of your waistline! Sugar is also a preserving agent. The Biology teacher in me wants me to go into all the technical details of sugar and osmosis but I said this wouldn’t be scary Science so here’s a brief summary from Moment of Science:
Sugar works not by poisoning the food-spoiling microbes, but by causing them to literally die of thirst. This is because sugar attracts water very well; the more sugar there is in any solution, the more water it tries to draw from its surroundings. This is bad news for any microbe that happens to be inside a jar of jam. High concentrations of sugar will suck the microbe’s vital water right through its cell wall, causing it to dehydrate. This process is called “osmosis” and it can be deadly for bacteria and mold.
Acidity is important for the gel to set. It won’t set if there is too little acid. In this recipe lemon juice is added to increase the acidity so that it gels well.
WHOAH. That was a lot of information! Well done you if you got to the end! Can you tell I’m a Biology teacher? I hope you learned something new and interesting about something we often take for granted – Jam!