1. Three Main Ways to Make Manju Skin Rise
Freshly steamed manju look soft and fluffy, quite different from dough that has only been kneaded. According to Kotobank, the "force" that creates this difference can be divided into three main methods [1].
Manju are sweets made by wrapping various fillings in a skin made from powders like wheat flour, rice flour, or buckwheat flour, and then steaming them. They are the representative type of steamed confection [1].
The three methods of leavening are distinct. The first is jōyo manju, which applies the rising power of yam. The second is sake manju, which utilizes the enzymes and fermentation of amazake (a sweet rice drink). The third is popular manju that use leavening agents [1]. These three methods differ in both ingredients and mechanisms. Let us first look at sake manju, which requires the most effort.
2. How Sake Manju Needs a Sake Seed Made Overnight
In a recipe from Hino City, Tokyo, dried koji and rice are left in water for one night (about 24 hours) to create a liquid sake seed. If the temperature of this liquid is kept above 30 degrees Celsius, it is said to start making fizzing and bubbling sounds [6]. It is thought that the source of this sound is gas bubbles produced by fermentation.
The process is a relay: enzymes in the rice koji turn the starch in the rice into sugar, and yeast uses that sugar to create carbon dioxide gas and other substances. This flow is what causes the dough to rise [1]. Here, the "sake seed" is not alcohol itself, but a fermented base liquid similar to amazake.
Sake manju, introduced as a local dish in Saitama Prefecture, were once made for fun using koji that families produced at home when making miso or soy sauce [7]. Today, methods using dry yeast for easier preparation are also introduced [7].
The Hino City recipe includes a method where part of the dough is dried and kept as a "seed" to use for the next fermentation [6]. The previous dough serves as the basis for the next fermentation.
3. How Sake Manju Dough Is Wrapped, Rested, and Steamed on High Heat
The method for making sake manju found in Yamanashi Prefecture materials follows this sequence: Mix the sake seed into wheat flour dough and let it rest until it becomes 2 to 3 times its original size (primary fermentation). Next, wrap the filling and let it sit at 25 to 30 degrees Celsius for 1 hour to 1.5 hours (secondary fermentation). Finally, steam it on high heat for about 30 minutes [5]. These figures are from one regional recipe and are not common to the whole country.
While steaming, steam cools and turns into water droplets that could fall on the dough and ruin the finish. The Hino City recipe suggests placing a dry cloth between the steamer lid and the pot to prevent water droplets from falling, steaming for about 20 minutes [6]. The Saitama Prefecture recipe suggests arranging them in a bamboo steamer lined with a wet cloth and steaming for 20 to 30 minutes [7]. Steaming times vary by recipe.
The Hino City recipe notes that because the condition of fermentation varies, sake manju do not always turn out exactly the same way. It encourages readers not to give up and to keep repeating the process [6]. This is both the interesting and difficult part of making sweets with living yeast. Is there a way to make them rise without waiting?
4. How Onsen Manju Rise Quickly with Baking Soda
Among the brown steamed manju seen as souvenirs in hot spring areas, some use baking soda (sodium bicarbonate). It is one kind of leavening agent [8].
According to the Osaka City Science Museum, sodium bicarbonate releases carbon dioxide when heated or reacted with acid. This creates many tiny bubbles, causing the dough to rise [8]. Unlike yeast, there is no need to cultivate and wait; bubbles appear simply by mixing and steaming. This is a major difference from sake manju.
This "no-wait" nature is thought to be one reason why popular manju using leavening agents are widely made [1].
The reason the skin turns brown cannot be pinned down to one cause. There is an explanation that it is due to a reaction involving sugar. On the other hand, there is also a story that the color comes from brown sugar. It cannot be decided definitively.
5. How Handling Bean Skins Changes the Red Bean Filling
According to the Ministry of Agriculture, Forestry and Fisheries' "Nippon Traditional Food Encyclopedia," "koshian" (smooth red bean paste) is made by removing the skins from cooked azuki beans, then adding water and sugar and kneading it [2]. If cooked beans are used as is, it is called tsubuan (chunky paste), and if the skins are crushed and mixed in, it is called tsubushi-an [2].
The key point about koshian is that the skins are removed and water and sugar are added. It is thought that the smooth mouthfeel is connected to not leaving the hard skins behind [2].
Home recipes include a preparation step called "shibukiri," where azuki beans are boiled and the water is discarded to remove astringency and bitterness before cooking again. It is said to result in a clean taste, but this seems to vary by recipe.
By the way, were manju in the past commonly filled with sweet paste as they are today?
6. The Legend That Manju Once Contained Meat
In China, there is a legend that manju began when Zhuge Liang wrapped lamb and pork in wheat flour skins and steamed them during the Three Kingdoms period. However, this is a legend and cannot be confirmed as historical fact [1].
In Japan, it is said that Hayashi Jouin, who came from the continent during the Muromachi period, introduced manju with azuki bean filling, marking the beginning of manju in Japan [2]. However, there is also a theory that Enni introduced them to Fukuoka, so the origin is not settled on one point [2].
At Kankou Shrine in Nara City, there is a shrine dedicated to Hayashi Jouin, and a Manju Festival is held every year on April 19 [3].
It is said that during the Muromachi period, both meat-filled manju and sweet bean paste manju existed. It is thought that sweet bean paste manju became mainstream due to the idea of avoiding meat [1]. Additionally, it is explained that Zen Buddhist monks introduced "dim sum" such as yokan and manju from China during the Kamakura to Muromachi periods [4].
7. How to Spot Differences from the Ingredient List and the Cross-Section
You can check the ingredient list on the back of the box or bag of manju bought at a store. Look for names of ingredients that leaven the skin, such as yam, koji, or leavening agents. Labels differ by product, so differences in how they are written can also be clues.
Another method is to cut the manju in half and compare the cross-section of the skin. You can visually compare if there are differences in the size or arrangement of the bubbles. However, you cannot determine the leavening method solely by appearance.
Recipes for sake manju are written in materials from Yamanashi Prefecture, Hino City, and Saitama Prefecture [5][6][7]. Even with the same name, times and temperatures differ slightly by region. The action of baking soda can be read in detail in the explanation from the Osaka City Science Museum [8].