Yōkan — firm red-bean jelly set with agar

i. Origin & history

The name is a surprise: 羊羹 means 'sheep soup'. It comes from the Chinese yanggeng, a thick mutton broth that set into a jelly when cool. Zen Buddhist monks who studied in China brought the dish to Japan in the Kamakura and Muromachi periods (thirteenth to fifteenth centuries), but as vegetarians they could not eat mutton. They recreated it with azuki beans and wheat flour, steamed into a firm cake, and served it as a tenshin, a light snack eaten with tea. The name stayed, even though the mutton went.

That steamed form, mushi-yōkan, is still made. The modern neri-yōkan ('kneaded yōkan') appeared in the Edo period (1603–1868), after the discovery of kanten, agar made from freeze-dried seaweed jelly. The story usually told is that kanten was discovered by chance in Kyoto in the mid-seventeenth century, when a dish of seaweed jelly was left out in the winter cold. With kanten, bean paste could be boiled down and set into a smooth, glossy block that kept far longer than steamed versions.

Neri-yōkan became a luxury of the Edo merchant class and a fixture of the tea ceremony. Long-established confectioners such as Toraya, which traces its history in Kyoto back to the sixteenth century, made yōkan a byword for quality, and blocks wrapped in paper or bamboo leaf are still classic formal gifts. A softer, lighter mizu-yōkan ('water yōkan') with less agar and sugar is a summer sweet, served cold.

Neri-yōkan's high sugar content and low moisture make it remarkably durable. Sealed yōkan keeps for months, and long-life versions are sold as emergency food and as energy snacks for hikers and soldiers.

ii. Why yōkan keeps — and how to get the gloss

Neri-yōkan is a concentrated mixture of bean paste, sugar and agar. The sugar, often as much as the weight of the beans, binds water so tightly that there is little left for microbes to use; this low 'water activity', together with cooking down the mixture, is why traditional yōkan keeps for so long. It is preserved in the same way as fruit pastes such as quince paste.

Kanten sets very differently from gelatine. It must be boiled for a few minutes to dissolve fully, it sets firmly at room temperature, and it does not melt again until heated far above body temperature. That gives yōkan its firm, clean-cut texture and lets it be stored and served at room temperature. Undissolved agar leaves the yōkan weak and grainy, so the kanten is always boiled in water first, before the paste and sugar go in.

The 'kneading' in neri-yōkan means stirring the hot mixture constantly as it cooks down. This prevents scorching, drives off water and develops the deep, glossy surface. The mixture is ready when it falls from the spatula in thick, slow ribbons; a few drops on a cold plate should set within a minute.

Before pouring, the mixture is cooled slightly while being stirred. Poured too hot, the bean solids can sink, leaving a pale layer of clear jelly on top. Stirring until it thickens a little keeps the block uniform. A spoonful of mizuame or glucose syrup adds shine and keeps the surface from crystallising.

iii. Ingredients

Makes 12 servings · scroll the side panel to adjust

• 4 g kanten (agar) powder
• 300 ml water
• 150 g granulated sugar
• 500 g sweetened smooth red-bean paste (koshian)
• 1 tbsp mizuame or glucose syrup (optional)
• ⅛ tsp salt
• 6 candied chestnuts (kuri kanroni), halved (optional)

Kanten powder is the easiest form of agar to measure; if using a kanten stick, soak half a stick (about 4 g) in water for an hour, squeeze and tear it into the pan. Agar flakes need about three times the weight. Use koshian, smooth sieved red-bean paste, for the classic silky yōkan; tsubuan, with whole beans, makes the more rustic ogura yōkan. Ready-made koshian is already sweetened, so this recipe adds less sugar than traditional formulas; add up to 100 g more for a firmer, longer-keeping yōkan. Salt rounds out the sweetness.

iv. Method

1. Line a 15 × 15 cm or 20 × 10 cm tin with cling film, or wet a yōkan mould with water. If using chestnuts, set them aside.
2. Whisk the kanten into the water in a saucepan and leave for 5 minutes. Bring to the boil, stirring, and simmer for 2 minutes until the agar has completely dissolved.
3. Add the sugar and stir until dissolved. Lower the heat and add the bean paste in three or four additions, stirring until smooth after each.
4. Cook over medium-low heat, stirring constantly with a heatproof spatula and scraping the base, for 10–15 minutes, until the mixture thickens and falls in thick ribbons. A drop on a cold plate should set within a minute.
5. Stir in the mizuame and salt, cook for 1 minute more, then take off the heat and stir for 2–3 minutes until slightly cooler and thicker.
6. Pour into the tin and smooth the top. If using chestnuts, press them in now so they are suspended in the yōkan.
7. Leave to set at room temperature for 1 hour, then chill for at least 2 hours. Turn out and cut into 1 cm slices with a wet knife.

v. Tips & common mistakes

• Boil the kanten fully before adding the paste. Undissolved agar leaves a weak, grainy set.
• Stir constantly. Bean paste scorches easily, and burnt flecks ruin the colour and taste.
• Test the set on a cold plate. If the drop stays liquid, cook a few minutes more.
• Cool slightly while stirring before pouring. This stops the bean paste sinking and a clear layer forming on top.
• Use a wet knife. It gives clean, glossy slices; wipe and re-wet between cuts.
• Keep it wrapped. Exposed yōkan dries and its surface crystallises.

vi. Variations

Mizu-yōkan, the summer version, uses about 2 g kanten, 400 ml water, 300 g koshian and 50 g sugar, and is served chilled in small cups. Kuri yōkan contains chestnuts; ogura yōkan uses whole beans; shiro yōkan uses white-bean paste, and matcha yōkan adds green tea to white-bean paste. Imo yōkan, a Tokyo speciality, is made from sweet potato, and mushi-yōkan is steamed with flour rather than set with agar. Layered and clear yōkan with fruit are made for summer.

For other bean-paste sweets, see daifuku, monaka and zenzai, and for agar desserts, anmitsu and the Indonesian-style agar-agar jelly. The Chinese mung bean cake is another dense bean sweet for tea.

vii. Serving & storage

Serve yōkan in thin slices, about 1 cm, with strong green tea — sencha or matcha — whose bitterness balances its intense sweetness. Use a wooden pick (kuromoji) or small fork. One or two slices per person is enough.

Wrapped tightly in cling film, homemade yōkan keeps for up to 2 weeks in the fridge or about a week at cool room temperature. Mizu-yōkan, with less sugar, keeps for 3–4 days chilled. Do not freeze it; agar gels weep and turn spongy when thawed.

ix. More from Japanese

• Anmitsu — agar jelly with bean paste
• Kuzumochi — kudzu starch jelly
• Daifuku — mochi with bean filling
• Monaka — crisp wafers with bean paste
• Zenzai — red-bean soup with mochi
• Mung Bean Cake — Chinese pressed bean sweet