Agar-Agar Jelly — layered pandan and coconut jelly

i. Origin & history

Agar is extracted from red seaweeds (chiefly Gelidium and Gracilaria), boiled to release their gelling carbohydrates and then dried. Seaweed jellies have long been eaten in East Asia, and agar as a dried product is usually traced to Japan, where it is called kanten. The story told in Japan is that in the mid-seventeenth century an innkeeper threw out leftover tokoroten (seaweed jelly noodles) in winter, found it had frozen and dried into a light, white substance, and discovered it could be re-boiled into jelly. Whether or not it happened that way, freeze-drying became the traditional way to make kanten.

The word 'agar-agar' itself is Malay, originally the name of a local seaweed and of the jelly made from it, and the Malay name became the international term. In the Malay world, agar jellies are part of everyday cooking: agar-agar santan (coconut milk jelly), pandan jelly, palm-sugar gula melaka jelly and elaborate jelly moulds set with fruit or shaped like flowers for Hari Raya, weddings and birthdays. Nyonya (Peranakan) cooks are famous for multi-coloured layered jellies.

In southern China and Hong Kong, agar is called daai coi (大菜, 'big vegetable') or yeung coi, and agar jellies — coconut, osmanthus, red bean, mango — are standard home and dim sum sweets. It is sometimes confused with liángfěn, which is a starch jelly made from mung bean or pea starch, and with grass jelly, which is made from a herb; neither contains agar.

Agar was also important in science: since the late nineteenth century it has been the standard medium for growing bacteria in laboratory dishes, precisely because it stays solid at warm temperatures. That same property is what makes it so useful in hot climates.

ii. How agar behaves, and why it is not gelatin

Gelatin is an animal protein that dissolves in warm liquid, sets only in the fridge and melts again around body temperature — which is why gelatin jelly is soft, wobbly and melts in the mouth. Agar is a plant carbohydrate with very different behaviour. It will not dissolve until it is boiled; it then sets as it cools to about 35–40°C, which means at room temperature and in minutes; and once set it does not melt again until it is heated to around 85°C. That gap between setting and melting is why agar jelly can sit on a hot table without collapsing.

It also sets much more firmly. Agar gives a jelly that cuts cleanly with a knife and has a crisp, slightly brittle bite rather than a bounce. Roughly 1 teaspoon (2 g) of agar powder firmly sets about 250–300 ml of liquid. Agar strands and flakes are weaker by weight than powder, so recipes are not interchangeable without adjusting — roughly three times as much flake as powder.

Two things weaken it. Strong acid (citrus juice, pineapple) boiled with agar breaks it down, so acidic juices are stirred in after boiling. And skimping on the boil leaves undissolved agar, giving a weak, grainy set. Agar must simmer for at least two minutes after it is fully dissolved.

Layering exploits the fast set. Each layer is poured once the one below has set enough to hold it but is still warm and slightly tacky, so the two fuse. If a layer sets fully and cools, the next one may slide off when cut; scratching the surface lightly with a fork before pouring helps it grip.

iii. Ingredients

Makes 12 servings · scroll the side panel to adjust

• 10 pandan leaves, cut into pieces
• 650 ml water (pandan layer)
• 5 g agar powder (pandan layer)
• 110 g sugar (pandan layer)
• 400 ml coconut milk
• 200 ml water (coconut layer)
• 5 g agar powder (coconut layer)
• 90 g sugar (coconut layer)
• ¼ tsp salt

Use agar powder, sold in small sachets in Asian shops (or as kanten powder in Japanese shops); if you only have strands, use about 15 g per layer and soak them first. Fresh or frozen pandan leaves blended with water give colour and the real grassy-vanilla aroma; a few drops of pandan paste can stand in, with ½ tsp in the plain water. Full-fat coconut milk gives a rich, opaque white layer. The salt sharpens the coconut. The whole jelly is vegan and gluten-free.

iv. Method

1. Blend the pandan leaves with 200 ml of the pandan-layer water until fine, then squeeze through a sieve or muslin. Combine the green juice with the remaining 450 ml water.
2. In one saucepan, whisk 5 g agar powder into the pandan water and leave 5 minutes. In a second pan, whisk the other 5 g agar into the coconut milk and 200 ml water.
3. Bring the pandan mixture to the boil, stirring, add 110 g sugar and simmer for 2–3 minutes until no granules remain. Keep it on the lowest heat.
4. Bring the coconut mixture slowly to a simmer, stirring constantly so it does not catch, add 90 g sugar and the salt and simmer for 2–3 minutes. Keep it on the lowest heat too.
5. Rinse a 20 cm square tin with water. Pour in a quarter of the pandan mixture and leave for 3–5 minutes, until the surface is set when touched lightly but still warm and tacky.
6. Gently ladle a quarter of the coconut mixture over the back of a spoon onto the set layer. Wait until set, then add the next pandan layer. Continue alternating to make 8 layers, stirring each pot before pouring.
7. Leave at room temperature for 30 minutes, then chill for at least 1 hour until cold and firm.
8. Run a knife round the edges, turn out and cut into squares or diamonds with a sharp, wet knife.

v. Tips & common mistakes

• Boil it properly. Agar only dissolves at a full boil. Under-boiled jelly sets weakly and tastes gritty.
• Keep both pots warm. Agar starts to set at about 40°C. If a pot begins to gel, simply reheat it until liquid again — agar can be re-melted without harm.
• Pour onto a warm, tacky layer. Too early and the colours mix; too late and the layers separate when cut. Test with a fingertip.
• Pour gently over a spoon. This stops the hot liquid breaking through the thin set layer below.
• Add acid last. If you add citrus or pineapple juice to a variation, stir it in after boiling and off the heat.
• Measure the agar exactly. A gram or two too much makes the jelly hard and rubbery; too little and it will not cut cleanly.

vi. Variations

Gula melaka jelly replaces the sugar in the clear layer with palm sugar. Agar-agar telur includes beaten egg, which separates as it sets into a custardy layer and a clear one. Fruit jelly sets mango, lychee or longan pieces in a clear or juice-based agar. Butterfly pea jelly uses the blue flower for colour, and a squeeze of lime turns it purple. In Hong Kong, osmanthus jelly sets dried osmanthus flowers and goji berries in clear agar.

For coconut jelly set in the coconut shell, see coconut jelly; for Japanese agar sweets, try anmitsu and the red bean block yokan; and for the steamed layered cousin made with rice flour, see kue lapis.

vii. Serving & storage

Serve agar-agar jelly chilled, cut into neat squares, as an afternoon snack, a light dessert after a spicy meal or part of a festive spread. It is a staple at Hari Raya open houses, children's parties and Chinese New Year in Malaysia and Singapore, and it is easy to transport because it does not melt.

Keep it covered in the fridge for up to 4 days. Over time it may weep a little liquid (syneresis); simply drain it. It does not freeze — ice crystals destroy the gel and it thaws into a spongy, watery mess, which, as the kanten story suggests, is how agar is dried, not how jelly is kept.

ix. More from Chinese

• Coconut Jelly — set in the coconut shell
• Taro Cake — steamed taro and coconut cake
• Tangyuan — glutinous rice balls
• Anmitsu — Japanese agar dessert
• Kue Lapis — Indonesian layered cake
• Butterfly Pea Flower Pudding — blue flower jelly