Castella (kasutera) is a beloved Japanese sponge cake — dense yet astonishingly tender, faintly honeyed, with a deep brown top and a fine, even golden crumb. It is most associated with the port city of Nagasaki, where it has been made for centuries and remains the city's signature edible souvenir, sold in long boxed loaves.
What makes castella fascinating is its lineage. It is a Japanese icon, but its name and origin are Portuguese — a relic of the first European contact with Japan, absorbed and refined over four hundred years into something entirely its own.
Pão de Castela: a cake from the age of trade
Castella arrived with the Portuguese in the sixteenth century. Missionaries and traders reached Nagasaki — then one of Japan's only windows to the outside world — and brought with them a sugar-rich sponge bread. The Japanese name kasutera is thought to derive from the Portuguese phrase "pão de Castela," meaning "bread of Castile," a reference to the Spanish kingdom of Castile.
Sugar was rare and precious in Japan at the time, so a sweet, keeping cake was a luxury and a novelty. Nagasaki, as the hub of this early European trade, became its home, and the cake outlived the trade itself — Japanese confectioners kept making and improving it long after Portuguese contact waned, turning a foreign import into a national treasure.
Just eggs, sugar, flour — and no butter
Part of castella's charm is its near-austere ingredient list. A classic castella is built from only a handful of things:
- Eggs — whipped to a thick foam, they provide nearly all the structure and lift; there is no chemical leavening in the traditional recipe.
- Sugar — for sweetness, but also for moisture and the deep colour of the crust.
- Flour — notably bread flour (high-gluten), unusual for a cake; it gives castella its characteristic slightly chewy, springy body rather than a crumbly tenderness.
- Starch syrup (mizuame) — a clear, thick Japanese sugar syrup that keeps the cake moist and supple for days.
Crucially, there is no butter and no dairy at all. Castella is essentially a refined egg-foam sponge, which is why it depends entirely on technique — see our pastry fundamentals for how whipped-egg sponges get their rise.
Honey for flavour and moisture
The defining flavour note of modern castella is honey. Stirred into the batter, it contributes the cake's gentle, mellow sweetness and its signature aroma, while also drawing in and holding moisture so the crumb stays soft. Together with the mizuame starch syrup, honey is the reason a well-made castella tastes fresher and moister days after baking than most plain sponges.
This emphasis on lasting moisture is part of what separates castella from a Western genoise: it is engineered to be a keeping cake, traditionally rested for a day after baking so the texture settles and the honey flavour deepens.
Wooden frames, a brown top and sugar at the base
Traditional castella is baked in tall wooden frames rather than metal tins. The wood moderates the heat gently and evenly, helping the cake rise tall with a uniform, fine crumb and a flat, level surface — important for a cake sold in neat rectangular slices.
Two visual signatures result from the bake. The top develops into a deep, glossy brown as the sugars caramelise, forming a thin skin that contrasts with the pale interior. And at the very bottom you will often find a layer of crunchy sugar crystals (zarame) — coarse sugar deliberately sprinkled into the base of the frame, which does not fully dissolve and leaves a pleasant grainy crunch beneath the soft sponge. That base layer is prized by connoisseurs as a mark of a properly made loaf.
Castella today
Castella remains the iconic souvenir (omiyage) of Nagasaki, where long-established confectioners sell it in elegant boxed loaves. Beyond the plain original, modern shops offer variations flavoured with matcha (green tea), brown sugar (kokutō), chocolate or honey, and a popular bite-sized version called castella baby cakes or fish-shaped baby castella sold at festivals.
It is a perfect example of how Japanese confectionery absorbs an outside technique and refines it to a whisper of its former self. For another example of that precision, see the mille crêpe cake, and explore the wider tradition in our overview of the pastries of Japan. Its soak-and-moisture philosophy also makes an interesting contrast with the milk-drenched tres leches cake.
Frequently asked questions
Is castella Japanese or Portuguese?add
Both, historically. The cake was brought to Nagasaki by Portuguese traders and missionaries in the sixteenth century as "pão de Castela" (bread of Castile). Japanese confectioners then adopted and refined it over centuries into the distinct cake known today as castella.
Does castella contain butter or dairy?add
No. Traditional castella is made without any butter, milk or other dairy. Its richness and tender texture come from whipped eggs, sugar, honey and starch syrup, with bread flour providing the structure.
Why does castella use bread flour instead of cake flour?add
The higher-gluten bread flour gives castella its characteristic springy, slightly chewy body and helps it rise tall and hold a fine, even crumb. It is one of the details that distinguishes castella from a softer, more crumbly Western sponge.
What are the sugar crystals at the bottom of castella?add
They are coarse sugar (zarame) sprinkled into the base of the wooden baking frame. It does not fully dissolve during baking, leaving a thin crunchy layer beneath the soft sponge — a feature prized as a sign of an authentic, well-made castella.