Water roux, also known as yu-dane (Japanese: 湯種, romanized: yu-dane) or tangzhong (Chinese: 湯種; pinyin: tāngzhǒng), is a paste of flour cooked in water or milk which is used to improve the texture of bread, making it soft and fluffy.
For yu-dane the flour is mixed with an equal weight of boiling water poured over it. This mixture then holds moisture so that, when it is added to a bread mix, the dough bakes with a soft, fluffy texture and the bread then keeps for longer.
For tangzhong the flour is cooked at 65 °C (149 °F) in the liquid which causes its starch to gelatinize. The gelatinized roux is generally used at a moderate temperature and apparently also contributes to slightly greater rise during baking.
"Scalding" flour, especially rye flour, for baking is a technique that has been used for centuries.
The Pasco Shikishima Corporation (Japanese: 敷島製パン) was granted a patent in Japan for making bread using the yu-dane method in 2001. The yu-dane method was then modified by Taiwanese pastry chef Yvonne Chen (Chinese: 陳郁芬), who published a book in 2007 called 65°C Bread Doctor (Chinese: 65°C 湯種麵包), borrowing the Japanese term 湯種 directly. This book popularized the technique throughout Asia.
In 2010, food author Christine Ho first wrote about the technique in English, using the Mandarin pronunciation of 湯種, tangzhong. She subsequently wrote more than twenty recipes using the method, which helped popularize the technique in the English-speaking world.
Breads made by the scalding method have been eaten for centuries...