Purple Sweet Potato Mochi 紫薯糯米糍

Mid autumn festival is already over but I still have several purple sweet potatoes and half a carton of coconut cream lett in my fridge after making my mooncakes (read about my blog posts, Coconut Purple Sweet Potato Snow Skin Mooncakes and Crispy Coconut Sweet Potato Mooncakes). I turned the leftover ingredients into mochi in the morning while my kids were at school. The kids enjoyed snacking on these smooth and elastic mochi after school and my younger son who loves to eat even requested to bring one to school for lunch the next day. Fortunately, mochi made with Japanese sweet rice flour could stay soft for two days and therefore wouldn’t deteriorate and turn into dry and stiff balls overnight.

The mochi dough can be made with both shiratamako and mochiko flour. It is easier to get access to mochiko flour here in Toronto as shiratamako flour can almost only be found in Japanese grocery stores. I used Okinawan sweet potatoes for my filling because of its creamier texture and vibrant bluish purple color when cooked. These white-skin-with-mottled-purple-interior sweet potatoes contain less fibrous strings than purple sweet potatoes, making it a smoother filling. Since sweet potatoes differs in sweetness and moisture level, season them according to personal taste and add more liquids such as milk, whipping cream or water to adjust the consistency as needed.
糯米皮可以白玉粉或日式Mochiko糯米粉(もち粉)製作,在多倫多只有在日式超市才能找到白玉粉,因此EC一般使用較常見的Mochiko糯米粉。 餡料方面EC使用夏威夷紫薯,白皮紫芯的夏威夷紫薯比一般紫芯蕃薯少呈絲狀的纖維組織,口感更覺幼滑,蒸熟後是深深的紫藍色十分鮮艷。紫薯的甜度及水份有異,因此可依個人口味增減糖量以及牛奶、淡忌廉或水等液體份量來調校甜度及黏度。

Below table shows the ingredients represented as both baker’s and true percentages for easy calculations.

Baker’s %
True %
Mochiko flour
85 26.9
Rice flour
15 4.7
Icing sugar
40 12.7
Coconut cream
83 26.3
83 26.3
Grapeseed oil
10 3.1
316 100


Purple Sweet Potato Mochi

Makes 14


For the Mochi Dough
153 g Mochiko sweet rice flour (can be replaced with Shiratamako flour)
27 g rice flour
72 g icing sugar
150 g milk
150 g coconut cream
18 g grapeseed oil
Potato starch (katakuriko) for coating, as needed

For the Purple Sweet Potato Filling
320 g purple sweet potato, cooked (I used Okinawan sweet potatoes)
50 g demerara sugar
35 g coconut oil
15 g maltose
35 g whipping cream


日式Mochiko糯米粉(もち粉) 153克 (可用白玉粉代替)
粘米粉 27克
糖粉 72克
牛奶 150克
椰漿 150克
葡萄籽油 18克
片栗粉(防沾用) 適量

紫薯 (已蒸熟) 320克 (EC用夏威夷紫薯)
原蔗糖 50克
椰子油 35克
麥芽糖 15克
淡忌廉 35克

Directions 做法

For the Mochi Dough 糯米皮
Place Mochiko flour, rice flour and icing sugar in a large microwave-safe bowl then whisk to combine. Add oil, milk and coconut cream and mix well with a whisk until smooth.

Cover bowl with plastic wrap or microwave-safe lid. Microwave on high for 2 minutes. At this time the mixture should be firm around the edges but remain runny in the center. Remove and stir well with a wet spatula. Cover and microwave again for another minute. Remove and stir to check for doneness. If the mixture has not completely set to form a dough then return to the microwave to heat in 30-second intervals. Microwave differs in wattage and model (mine is 1100W) so adjust heating time accordingly. Alternatively, pour mixture in a shallow plate and cook by steaming for 20 minutes.

Scrap dough into another plate. Flatten dough and cover the surface with plastic wrap to prevent dough from drying out. When the dough has cooled slightly, put on disposable gloves and knead dough until it is smooth and elastic. Keep covered and let cool to room temperature.

For the Purple Sweet Potato Filling 紫薯餡
Wash and peel the purple sweet potatoes. Cut into cubes or slices and steam for 15 to 20 minutes until tender (I steamed mine with electric pressure cooker and see recipe here). Transfer freshly steamed purple sweet potatoes into a large bowl and stir in sugar, whipping cream and coconut oil until sugar has dissolved. Mash with a spoon until incorporated. Pass mixture through a medium mesh sieve for a smooth-textured filling. Press a piece of plastic wrap directly on top of the filling to prevent drying then set aside.

For Shaping 包餡
Divide purple sweet potato filling into 14 portions of 30 g each. Roll each into a ball (wear disposable gloves to prevent sticking). Cover and refrigerate for 10 minutes until firm.

Place potato starch in a plate and set aside for coating. Measure 40 g of mochi dough. Working with both hands,flatten dough into a disc that is thinner around the edges. Place a ball of filling in the middle then wrap and seal the edges by pinching them together. Shape stuffed dough into a ball again then coat lightly with potato starch. Brush off excess powder and place mochi seam side down in a paper cupcake liner.

Repeat with remaining mochi dough and filling. Store mochi in an airtight container and consume within two days. Serve at room temperature or warm by reheating in the microwave for 8 to 10 seconds.

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