No more shrinkage ! 不再回縮

light cheesecake after the shock treatment

This is another great illustration on how understanding science helps me to be a better baker. Ever since I started baking cakes, especially light cheesecake, the issue of shrinkage always bothered me. I carefully and diligently beat up the egg white to stiff peaks and folded it in with the batter. I hoped that the air that was incorporated would expand due to the oven's heat and produce a nice and fluffy cake. But I was disappointed to notice the cake gradually shrank after a few minutes out of the oven.




Of course, it is a scientific fact that when an object is cooled, it will contract as opposed to the fact that an object will expand when heated (冷縮熱脹). Therefore, I followed the advice of Junko and let the cake cool slowly inside the turned off oven so that the amount of shrinkage would be reduced. This is what it looked like:

light cheesecake slowly cool inside the oven for more than 30 minutes after baking. No shock treatment. Notice the waist around the whole cake.

It looks better than a collapsed or compressed cake. But how come it has a "waist" ???.....

Recently, I browsed other blogs and read a post on  Honey Castella Cake from Biren's blog. After baking this Japanese cake, she dropped the whole cake, still in the pan, from a foot high to prevent it from shrinking. Skeptical in the beginning, I asked her for her reasoning and she referred me to an article that was written in the 70's by a few Japanese workers (written in English) from a flour milling company in Tokyo.

It is not a very long paper but essentially they did some experiments on the effects of shock treatment on cake volume and concluded that dropping a cake from a height of 10cm/4 inches would give the greatest volume to the cake. They went on to explain that when the cake is in the hot oven, the airtight structure of the cells expand under the inner pressure of the air that is already whipped in (stiff peaks of egg whites). At the end of baking, the cake is set because all the cells are rigid.

chiffon cake after the shock treatment, without inverting

But as the cake is taken out of the oven to expose to cooler air, the cells contract and cause shrinkage. One way to correct this is to create cracks in the cell walls by dropping the cake. This relieves the pressure.

This was truly an eye opening experience for me. Even though I extensively read a number of cookbooks, I have not yet encountered an author who covers this concept. This paper has been out for more than 30 years!

Not only does this method work on cheesecake, I tried it on a chiffon cake and it worked as well. Conventionally chiffon cake needs to be inverted for cooling to prevent collapse and shrinkage. However, I applied the shock treatment and let the cake cool on a rack. I did not find any change in volume.

Hopefully this information can help you with a better baking experience.

Note: Do not invert the pan to cool after shocking because it may have detached from the pan already.

Ref: H. Ohtsubo, T. Kanbe, Y. Kaneko and S. Nomura, "Prevention of shrinkage after baking." Cereal Chemists, (1978): p.361

蛋糕焗後不回縮的竅門

如果你有焗蛋糕的經驗,我想你曾幾何時都或多或小有以下經歷:蛋糕在焗爐內理想地升高,但出爐後不久便像洩了氣的氣球一樣,十分腦人。原本鬆軟的蛋糕變成死死實實,真是令人氣餒 !

究竟怎樣才能焗出鬆軟可口,而又美觀,賣相精美的蛋糕呢?

我相信要明白一些基本科學知識,比只是一味死跟步驟,對烘焙成果有莫大益處。首先要明白蛋糕鬆軟的成因。除了要準備新鮮的材料之外,技巧便是另外一個主要因素。(其它還有爐溫,焗盤等都會影響成果,但本文只集中討論技巧中的一環)當你攪打蛋液--無論是打全蛋或分蛋或打蛋白--目的是將空氣打入蛋糊內,當這些空氣在爐溫下受熱膨脹,蛋糕便會升起。但當蛋糕焗好出爐,它便遇到較冷的空氣,冷縮熱脹這基本的科學真理便程現在你眼前。對一些比較脆弱或幼細的蛋糕,如日式海棉芝士蛋糕,因麵粉份量很少,全靠雞蛋凝固後的支撑力,怎樣避免回縮便是一大挑戰。

我曾經試過讓焗好的蛋糕仍然留在熄了火的爐內半小時至一小時,令它慢慢降溫,但效果都只是一般:

焗好慢慢在爐內降溫,有一條"腰"

直至最近我從另一個網誌內發現一種方法,可以改正這個缺點。Biren 將剛焗好的蛋糕連焗盤從高處放手,令它跌在櫃臺上,便可避免回縮現象。起初我滿心懷疑是否可行,但她讓我讀了一篇研究文章,令我明白到箇中因由。
原來三十多年前日本一所麵粉廠,有研究人員做過實驗,發現如果將剛焗好的蛋糕(連焗盤)從四寸高放手令它跌在櫃臺上,便可避免回縮現象。理由是蛋糕之所以回縮,是因為內裏的細胞壁受冷而收縮,但如果將它們震破,那麼壓力沒有了,回縮便不成問題!

這個研究實在令我茅塞頓開! 使我急不及待去試試:

日式海棉芝士蛋糕,經過震盪後,"腰"不見了!

除了這款輕芝士蛋糕,我也用雪紡蛋糕來做試驗:

效果實在是超乎理想,以後做雪紡蛋糕都不用倒扣了!

希望這些資料可以幫到大家焗出樣子精美又可口的蛋糕。

注意:蛋糕連盤震跌後不可倒扣,只須放在架上待冷便可。