○(日本語は下).

Historical Background of the Invention of Electrode Rice Cooker／Bread Machine and Reproduction Experiment with Evaluation (about so-called Denki-Pan in Japan and PANKO)

○Summary
１．Overview of Method

Today, we are converting electrical energy into thermal energy and making use of it. There are various devices on the market for baking bread. In the days after World War II, when supplies were scarce, people made their own bread baking machines like the one shown in Fig.1, and they became quite popular. This is called an electrode bread machine ,or simply a "Denki-Pan" machine in Japanese. Liquid steamed bread dough made of flour, salt, and sugar dissolved in water is poured between two electrode plates, and an altenating current of 100 volts(V) is applied.

Fig.1. Configuration of the bread baking machine

Fig.2. (Top) Power value for steamed bread (○), cooked rice (×), and yeast-fermented bread (＊). (Bottom) Time variation of water temperature. (power is current value×100) Current is a two-peak characteristic due to gelling and evaporation.

As a result of an evaluation, We found out that the thermal efficiency of those simple devices, which consistents of just two electrodes in a wooden box, is as high as approximately 70％. The reason for this is that the dough itself generates heat through Joule heat (electrolytes dissolved in water interferes with the movement of electrons and receives heat enaergy), instead of applying heat to the dough from the outside, as in an oven. 70％ of the added electrical energy is used for baking bread as heat of evaporation at 100℃. It was also found to have an excellent property to automatically turn off the electric current without a microcomputer after baking.

When an altenating current of 100V is applied for 9 minites in the process of baking. The water temperature rises monotonously and evaporates at 100℃, resulting in a two-peak current. This two-peak characterristic of current was found to occur as the starch gelatinization progressed and water evaporated(Fig.2).

The shape of the two peaks of the current will change because the sizing temperature range depends on the types of the starch. This same mechanism was used in the student experiment of cooking rice in a bread baking machine (rice, water, and salt, finished product is shown in Fig.3 (middle)). It was confirmed that even a dough of yeast-fermented bread similarly had a two-peak characteristic (made of strong flour, water, dry yeast, salt, sugar, and unsalted butter, finished product is shown in Fig.3 (right)). The rice can be cooked 20 minutes and the yeast-fermented bread can be baked in 14 minutes through energization. In the electrode type, the water temperature does not exceed 100 ℃, meaning the bread would not properly bake. The thermal efficiency of all three experiments are about 70％.

Fig.3. (Left) Finished original steamed bread: in 9 minutes. (Middle) Cooked rice: in 20 minutes. (Right) Yeast-fermented bread: in 14 minutes.

２．Electrode Type Bread Baking Machine

I found that this electrode type bread baking machine was invented by Shozo Akutsu, who formerly served the army in 1935. At that time, the reserch was not on steamed bread made of light wheat flour and baking powder, but on yeast-fermented bread made of strong flour dough that was energized. This technology was introduced for home use after World War II, mainly as steamed bread (today's so-called "Denki-Pan" in Japan).

This(Fig.3 (right)) corresponds to the reproduction of the electrode bread baking invented by Shozo Akutsu. In addition, the electrode bread later became bread crumbs for business use. In 1949, after World War II, electrode bread was dried in the sun and sold. Since then, manufacturers of bread crumbs have appeared.

Even today, half of the breadcrumbs used for commercial purposes are made by the crushing of the mentioned yeast-fermented electrode type pans. The process in the fermentation of the dough is the same at the factory, but when baking the dough, depending on the nature of the desired breadcrumbs, it is either the roasting type or electrode type that is used. The roasting method, in which heat is applied from the outside by an oven, requires preheating and is less efficient than the electrode method, where the dough itself generates heat, and the equipment is larger and less economical.

Since the electrode type does not truly bake the bread, the bread will not rise above 100℃ and produce white breadcrumbs that are harder than those of the roasting type and will not absorb oil as easily. The texture of the breadcrumbs did not degrade over time, so it was used by TableMark Co., Ltd.("Katokichi" in Japan) in Kagawa Prefecture, as batter for frozen fried shrimp, which became popular since the 1962.

Since 1960s, the export of breadcrumbs significantly increased, especially to the United States, where the electrode production method was also exported.

Additionally, in an electrode-type bread baking machine, the material of what the electrode plates made out of is crucial. This is because the material of the electrode plates are electrolytically corroded by energization and are leached out the dough. Thanks to the efforts of Mr. Yasuo Shimizu, who was the chairman of the technical committee of the National Federation of bread Crumb Industry Cooperatives, the government finally approved the use of pure titanium electrode plates in 1988, which are extremely resistant to corrosion. The Food Sanitation Law was also partially amended to allow this use, which solved the problem of the material of the electrode plates.

Breadcrumbs called "PANKO" in Japan were also recognized by the European Union, and "PANKO" was adopted as an English word in the Oxford English Dictionary in 2012.

Fig.4. (Hand-made)Reproduced yeast-fermented bread for breadcrumbs (Left: Equal 3,in 14 min. for electrode method, Right: Equal 5,in 29 min. for roasting method).

Fig.5. (Left) Professional electrode bread baking case for business use (pure titanium plate 50cm×50cm) (Right) And actual baked electrode bread for breadcrumb.

We also introduce an electrode type yeast-fermented bread, which is actually still manufactured in factories today. As shown in Fig.5. To further my reserch, I conducted an experiment(Hand-made) between the electrode type and the roasting type of bread crumb making. The process up to the second fermentation of the bread dough is the same for both.

The resulting bread with the electrode method is shown in Fig.4 (left) (Fig.3 (bottom), divided into three equal parts). And the bread baked in the oven (divided into five portions) is shown in Fig.4 (right) and bread is browned. Without any methods, it takes 29 minutes, including preheating(for 10 minutes), in the oven to bake the dough(for 19 minutes). But, with electrode type method, it implements the process in 14 minutes due to the process of energization. With this, we can feel the thermal efficiency. The white electrode type bread is not baked, so the aroma of yeast is more pronounced and delicious.

３．Electrode type rice cooker

The bread baking machine invented by Shozo Akutsu in 1935 was started with the former Army's orders of creating a food service vehicle ,which would be able to cook rice and bake bread, promptly as military equipment, no matter much it costs. Before the invention of the bread baking machine, a utility model of an electrode-type rice cooker with opposing electrode plates was developed by the former army in 1934. The electrode plates used for cooking rice were improved in 1936 to make them suitable for baking bread, and a bread making machine was incorporated. In 1937, the former army commercialized a food service vehicle(as the 97 model year type) that could cook rice and bake bread as a system that included a power supply. It was also deployed in the field.

In contrast, in the same year 1934, A patent for a method of cooking rice using the electrode type from Shuzo Hidaka was issued by the Japan Patent Office. This patent was issued 5 months before the utility model of rice cooking device using electrodes with opposing plates by Shozo Akutsu of the former army.

Shuzo Hidaka made the distance between the plates about 1cm so that rice could be cooked, even with tap water. If the distance is too wide, it will not be energized unless there is salt, etc. And the plates were arranged in a concentric circle along the bottom of a round rice container(called "Ohitsu" in Japan) without opposing. Hidaka invested the electrode type rice cooker shown in Fig.6 (right), despite not being commercialized for customer use. The former army made the electrode plates stand upright, while Shuzo Hidaka made them bottom-mounted. Using Hidaka's patent the National Nutrition Association, which was established within the Ministry of Health and Welfare, commercialized and sold an electrode rice cooker of the "welfare type"(for cooking 5 cups of rice) in May 1946 after the war(shown in Fig.6). In the instruction manual of this cooker, it is written that the National Nutrition Association took over the patent of Shuzo Hidaka, whose technology was converted by the army to home use in 1934 and manufactured it. However, at present, the relationship between Shuzo Hidaka, the former army, and Shozo Akutsu is entirely unknown, and the basis for this statement in the instruction manual cannot be confirmed.

Furthermore, a new utility model was proposed in March of 1946, which made a comb tooth shape(type) out of the electrode plate of the concentric circles of the "welfare type" and placed it on the bottom. Similar to what is shown in Fig.7 (right) and the "comb-tooth type" electrode rice cooker, which was called "Takara-Ohachi", was commercialized and sold. There are at least four "Takara-Ohachi"s in Japan, and they have become quite popular.

Fig.6. (Left) "welfare type" rice cooker(from the collection of Hiratsuka City Museum) (Right) Concentric circlar plate at the bottom of the container.

Fig.7. (Left) "comb-teeth" type rice cooker called "Takara-Ohachi" (from the collection of the Osaka City Museum) (Right) comb teeth shaped plate at the bottom of the container(released around 1947).

We made our own electrode type rice cooker using a commercial 180ml size(called 1"go" in Japan) sawara-wood "Ohitsu" (inner diameter: 11.6cm, height:6.2cm) ,which is similar to the one used in the "welfare" type (Fig.6 and Fig.9) and "comb-teeth" type of "Takara-Ohachi" (Fig.7 and Fig.8). In addition, we made a bottom-mounted electrode plate that resembles the "Takara-Ohachi" by bending the opposite electrode plates of the stand-upright case(shown in Fig.1), and made one in which electric current flows even with tap water (like Fig.10). In tap water, only 6 Watt current can flow through the side opposing plates(Fig.1), so rice cannot be cooked. The performance of each of these was evaluated in a reproduction experiment.

In three cases with the electrode plate spacing of 1cm at the bottom, it was confirmed that the rice could be cooked in about 20 minutes, even with tap water. The thermal efficiency of upright case(like Fig.10) was 70％, while that of the "Ohitsu" case(like Fig.8 and Fig.9), with its wide bottom and small internal volume, was 80％ and increased from 10％(is shown in Table 2). In the upright case, the thermal efficiency is same as 70％, even when salt is added.

As the result, the current characteristics show that gelling occurs even without salt, but the current is not affected by gelatinization because there is little electrolyte. For that reason, the first peak due to the start of gelling does not appear, it turned out to be one peak characteristics, and then only the second peak due to evaporation appears.

And in all three cases, the current becomes two peaks if salt is added. Additionally, the system of the bottom-mounted electrode type (Fig.8, Fig.9 and Fig.10) will wobble and become unstable at about current peak. The current fluctuates by about 50％ and becomes unstable, because of the bubbles on the bottom electrode plates when boiling. The current peaks at only 2A. The heat source is only at the bottom of the rice as bottom-mounted elctrode types, so the rice cannot be cooked evenly and does not taste very good. The current of a three types of rice cookers becomes unstable when salt is added as well (the current becomes two peaks, though). In the case of the old army method(Fig.1), where only opposing stand-upright plates are used, there is no wobble in the current and the rice can be cooked evenly from the sides, resulting in good performance.

Fig.8. (Left) Rice cooker with bottom-mounted comb teeth in the shape of a rice container(reproduction of "Takara-Ohachi" made by myself) (Right) Cooked rice: in 25 minutes.

Fig.9. (Left) Concetric rice cooker with a bottom-mounted rice container(reproduction of "welfare type" made by myself) (Right) Cooked rice: in 20 minutes.

Fig.10. Bottom-mounted comb-tooth shaped electrode plates in a stand-upright case of original (self-made reproduction) (Right) Cooked rice: in 20 minutes.

We confirmed that, on the other hand, wheat flower has about 4 times as much minerals(electrolytes) as rice, so even if the flower is just dissolved in the tap water and the dough is energized, it will have a two peak characteristic.

４．Electrode Sponge Cake

In addition to conventional liquid dough and yeast-fermented kneaded dough, we investigated the characteristics of foamy dough made with whipped whole eggs. I have never examined an electrode type sponge cake mentioned in previous research.

At first, We confirmed that the current characteristic of the pancake is the same as that of the steamed bread(a two peak characterictic), even with whole eggs mixed in.

Next, I made an electrode sponge cake by whipping whole eggs with a mixer, adding sugar and salt, shaking wheat flour, baking powder, melted unsalted butter, and milk to make a foamy dough, and then energizing it. The foamy batter is the same, but when it is baked in the oven, it needs to be preheated for 10 minutes to reach 180 ℃ and then baked at 180℃ for 25 minutes. So it is for a total of 35 minutes. With the electrode method, however, it can be done by only energizing for 14 minutes. It tastes good, although it only rises to 100 ℃ and does not bake.

Fig.12 "Electrode sponge cake" with whole egg whipped

At this time, for the foamy dough, the second current peak due to evaporation does not appear, but only the first current peak due to the start of gelling appears as one peak characteristics. The first peak appears because of the electrolyte. It is different from the one peak characteristic where only the second peak appears for the tap water cooking of rice. This is because the whole egg whipped foam dough solidifies the sponge structure of the dough after the end of gluing, and the current drop due to precipitation does not occur during evaporation. Also, due to the water content in the whole egg, the thermal efficiency cannot be calculated by the conventional method.