Purple Sweet Potatoes Chiffon

This must be the longest October for me.

I spent the first two weeks of the month sourcing for renovation contractors, reading up on renovation, visiting tile shops to select tiles, shopping around for lighting, bathroom sanitary ware, cooker hobs, oven, etc, etc. This is in preparation for my upcoming renovation of our house. The next two weeks were spent packing, packing and packing. On top of that, it was an anxious week when my elder son took the PSLE examination. I am glad that all went well, but before I could take a breather, it was soon my younger child's turn to sit for the year end school examination! Finally, his exam is over today. I am not done with packing yet...I still have to conquer the kitchen...which I have no choice but to leave to the last.

Anyway, I miss blogging...so I am here to share with you yet another chiffon cake recipe, before I dismantle my desktop computer and pack it into boxes.

This chiffon cake was made with purple sweet potatoes. I have came across two types of purple sweet potatoes...one of which comes with purple skin but the inside is yellow...and the other with both skin and the inside purple. This chiffon cake was made with the latter. It was by chance that I bought a bag of purple sweet potatoes. I actually wanted to get some spring onions and nothing else...but I was too shy to ask the stall owner. So I looked around and spotted the sweet potatoes...in the end I only paid for the sweet potatoes and the stall owner gave me the spring onions for free (^^')

There was no surprises when I went about preparing this chiffon cake. Although I must say, it was like attending some Chemistry lesson. I was amazed that the egg yolk batter, which was a deep purple because of the sweet potatoes, turn into a pretty pinkish batter the moment the few drops of lemon juice was added to it!

After the past few experiments in making chiffon cakes, I was quite satisfied with how this one turn out. The cake rose well in the oven, and it didn't shrink too much upon cooling :)

A few readers have asked me how I managed to unmold my chiffon cake nicely.  This time, I made it a point to take step by step photos to show all of you. I guess, the trick is to use a very thin bladed knife. When running the knife inside the cake pan, try to slide the knife as close to the inside of the pan, avoid slicing the cake crumb. I am not sure whether it is because of the quality or the type of cake pan that I am using, I am able to remove the cake effortlessly, without creating any mess. See photo 3 above...upon unmolding, there were not much crumbs left inside the pan.

I think it is also the type of cake pan that I am using, I always end up with chiffon cakes with 'pork-floss' like crust.

This chiffon cake was very soft and moist. The crumbs was a light pink...if the lemon juice were to be omitted, the crumbs would end up dull purplish. It was a fun experiment for me! This cake tasted really good, but I would still rank that banana chiffon cake as the best chiffon cake I have ever made ;)

I won't be sharing any baking post for the next two months as my kitchen is officially closed for renovation starting from today. However, I will still try to update my blog...but it will probably on the progress of my renovation or the holiday trips that we have planned.
 



Purple Sweet Potato Chiffon Cake

Ingredients:
(for 17cm or 7" tube pan)
(measurements in brackets are for 20cm or 8" tube pan)

40g  (70g)    egg yolks
50g  (80g)    water
40g  (70g)    vegetable oil
7g    (12g)    lemon juice
54g  (90g)    purple sweet potato, boil or steam, mashed
50g  (80g)    cake flour
10g  (20g)    caster sugar
70g  (120g)  purple sweet potato, boil or steam and diced into small chunks


110g (180g)  egg whites (cold from fridge)
55g    (90g)  caster sugar
5g     (10g)   corn flour

Method:

1. With the skin on, either boil with water or steam the purple sweet potato till soft (test with a fork, it should be inserted easily into the centre of the sweet potato). Leave to cool slightly and remove the skin. Mash and dice into small chunks accordingly.
2. Sieve cake flour, set aside. Sieve corn flour, set aside. 
3. Place egg yolks, water, mashed sweet potatoe in a mixing bowl. With a manual hand whisk, whisk the mixture to combine. Add in the vegetable oil, stir to combine. Add the lemon juice and stir to combine. (Note: the mixture will turn into light pink.) Sieve over the cake flour and whisk till the flour is fully incorporated and the mixture becomes smooth and sticky. Add in caster sugar, stir to combine.
4. In a clean, dry mixing bowl, beat egg whites with an electric mixer on low speed until mixture becomes frothy and foamy. Turn to high speed and gradually beat in the sugar, 1 tablespoon at a time, add in the corn flour together with the last tablespoon of sugar. Beat until the egg whites reaches the soft peak stage.The soft peak stage is reached when the peaks of the whites curl over and droop slightly. The egg whites should appear smooth and glossy. (Do not over beat the whites still stiff, it is better to beat the whites still soft peaks for easy folding with the yolk batter.)
5. Add the beaten egg white into the egg yolk batter in 3 separate additions, each time folding gently with a spatula until just blended.
6. Add the sweet potato chunks. Stir gently to combine.
7. Pour batter into a 17cm tube pan (do not grease the pan). Tap the pan lightly on a table top to get rid of any trapped air bubbles in the batter.
8. Bake in pre-heated oven at 160 degC for 35 mins, (for 20cm pan bake for 50 mins) or until a skewer inserted into the center of the cake comes out clean. (When lightly pressed the cake will spring back). Remove from the oven and drop the pan at a height of 20~30cm onto a table top. This action helps to keep the springy texture of the cake when it is left to cool.
9. Invert the pan immediately and let cool completely before unmould. To remove the cake from the pan, run a thin-bladed knife around the inside of the pan and the center core. Release the cake and run the knife along the base of the pan to remove the cake.

Recipe source: adapted from 戚风蛋糕秘法传授 by Noriko Ozawa

Sweet Potato