The Science Behind Aiyu Jelly
Published on 20 November 2020
Most of us who are fond of desserts and Taiwanese beverages have tried the chewy Aiyu jelly, one of the most popular toppings, but do you know how it is made?
Aiyu jelly is made from a plant called Jelly Fig. By rubbing a pouch of Jelly Fig seeds in boiled water at room temperature and letting the water extract sit for a while, the water will turn into a gelatinous substance like a magic trick. Why Aiyu jelly can be made by just rubbing the seeds in room temperature water without heating or cooling in the fridge?
The outer layer of Jelly Fig seeds is rich in pectin and pectinesterase (an enzyme), they gradually dissolve into the water during the rubbing process. Pectin is a long-chained polysaccharide. The pectinesterase modifies certain structures in the long-chained pectin, allowing pectin to combine with the metal ions in water (tap water in Hong Kong contains trace metal ions such as calcium ions and magnesium ions). This cross-linking reaction among pectin chains and metal ions forms a sponge-like network which traps water and results in a gelatinous substance.
Above diagram illustrates the cross-linking reaction
between the pectin and metal ions in the water
The fruit of Creeping Fig and the seeds inside it
Jelly Fig has a close relative in Hong Kong – the Creeping Fig. Both belong to ficus plants, and have similar fruit structure (both are syconium). As some books mentioned, a kind of dessert known as white jelly which was sold on the streets of Hong Kong before 1950s, was made from the Creeping Fig. The production process is similar to that of Aiyu jelly.
Pectin can be found in apples, grapes and many other fruits. It has a lot of applications in our daily lives, especially in the food manufacturing industry, such as making jam and yoghurt. Pectin is even used in producing cosmetic and personal care products, including lotion and shampoo. Fruits are really great for you!
Steps of making Aiyu Jelly
1) Get some Jelly Fig seeds and boiled water or mineral water at room temperature, the ratio is about 1 gram of seeds to about 50 ml of water.
- Note:
- Distilled water is not suitable, as it lacks metal ions.
- No grease on both hands and the apparatus. Grease will hinder the linking of pectin and metal ions.
2) Put the Jelly Fig seeds into a cloth pouch, then rub it gently in water for 10-15 mins. The pectin and pectinesterase will dissolve into the water gradually.
- Note:
- Do not rub longer than 15 mins and rub gently, otherwise Aiyu jelly may not set.
3) After rubbing, the water extract is pale yellow with increased thickness. Let it sit for 30-40 mins at room temperature, then the Aiyu jelly is set and ready to serve.
- Note:
- The sitting is to allow sufficient time for the pectin and metal ions to link, so do not stir the water extract after rubbing.
