Yukone Bread

The Japanese bread which utilizes a hot water processed dough, known as "yukone", lends itself to a fine, soft, fluffy texture with good keeping quality. The yukone dough is also known as hot water dough, gelatinized dough or occasionally interchanged with water roux (known in Chinese as tangzhong). The latter is a starch gel made using 1:5 flour to water.

Unlike many water roux or "65 degrees Celsius tangzhong" bread recipes favoured by Asian baking bloggers, the yukone bread contains around 60% less saturated fat and is thus less reliant on fat to prevent staling. The yukone dough is made by adding boiling water to flour so as to gelatinize the contained starch. Typically, the yukone dough is 1:1 flour to water. Some recipes suggest 10:7 flour to water.



The texture of the yukone bread results from hydration of the the starch, and proper development of gluten. Gelatinization swells the starch and allows formation of gas cells. Insufficient gluten development gives rise to softness that promotes large pores and loss of elasticity. Overworked gluten on the other hand gives dense textures as gas cells cannot expand.

Loaf volume decreases with increased yukone. At 20% flour weight yukone, the loaf height is reduced around 15% compared to a loaf without yukone. It appears 20% flour weight yukone gives the best volume for moisture.

Formula by Naito et al 2005:

Sponge
70 flour (12% protein)
44.8 water
2.2 yeast
0.1 yeast food
0.25 emulsifier
2 nonfat dry milk

Mix to stiff dough. Ferment in the fridge overnight.

Yukone (hot water dough)
20 flour
20 boiling water

Mix to a soft sticky dough. Maturate dough in the fridge overnight

Bread Dough
10 flour
10.2 water
6 sugar
2 salt
5 shortening

To make bread, mix fermented sponge and maturated yukone with the rest of the dough ingredients, except the shortening, to form a soft dough. Rest for 10 minutes. Knead to a smooth dough. Add shortening. Knead until the dough is stretchy. Kneading takes around 20 minutes by hand. Proof until double. Knock down. Knead well. Scale and shape. Proof until triple. Bake at 180 deg C for 30 minutes for a loaf, or 220 deg C for 15 minutes for rolls.

A recipe in table format can be found in Naito et al 2005.

Reference:
The Effect of Gelatinized Starch on Baking Bread
Shigehiro Naito, Shinji Fukami, Yasuyuki Mizokami, Rieko Hirose, Koji Kawashima, Hiroyuki Takano, Nobuaki Ishida, Mika Koizumi And Hiromi Kano
Food Sci. Technol. Res., 11 (2), 194-201, 2005

Study on Starch in White Bread Prepared by Yukone Processing
Tetsuya Yamada, Wakana Hasegawa, Tomomi Ito, Akihiro Ohara and Takuo Adachi
Faculty of Agriculture, Meijo Uni. Scientific Rept., 4, 9-20, 2004