打發蛋白時加糖的時間及意義[科學]+[技術]問題 ?

01-29

[科學]+[技術]問題
1. 為什麼要在打發蛋白一定階段後才能加糖？一開始加糖打發蛋白根本打發不起來。有什麼科學依據么？
2. 分次加糖的作用？

Sugar both hinders and helps foam making. Added early in the process, it delays foaming, and it reduces the foam』s ultimate volume and lightness. The delay comes from sugar』s interference with the unfolding and bonding of the proteins. And the reduction in volume and lightness is caused by the syrupy sugar-egg mixture being harder to spread into thin bubble walls. Slow foaming is a real disadvantage when the whites are whipped by hand — at standard soft-meringue levels, it doubles the work — but less so if you』re using a stand mixer.

The helpful thing about sugar is that it improves the foam』s stability. By making the liquid thick and cohesive, sugar greatly slows drainage from the bubble walls and coarsening of texture. In the oven, the dissolved sugar hangs onto the water molecules and so delays their evaporation in the high heat until after ovalbumin has had time to coagulate and reinforce the raw foam. And it eventually contributes reinforcement of its own in the form of fine but solid, cotton-candylike strands of dry sugar.

Sugar is usually incorporated into the egg whites after the foam has begun to form, when many proteins are already unfolded. For some purposes, cooks will mix sugar and whites at the outset, in order to obtain a very firm, dense foam.

"On food and cooking" - Harold McGee

誰說一開始加糖就打發不起來？器具都用紙巾擦乾了么？有油污否？糖的顆粒是多大的？蛋白裡面有沒有不小心混進了哪怕一丁點的蛋黃？

按照我自己的操作經驗，如果做一個八寸的蛋糕，完全可以把細砂糖分兩下加蛋白里，先放一半的糖，放蛋清，攪拌機打打，等有白色泡沫出來但是又不是很細密的時候再把第二部分糖邊攪拌邊放進去，然後打發時間還要參考攪拌機的檔速的。

剛開始你可以照書做，熟練了你就可以自己摸索了阿，人是活的哇！

在一開始加糖了打不起來嗎？這個事情得辯證的看。我在一開始加糖是可以打發的，但我加的糖分量少。有一次看教做蛋糕的視頻，糕點師建議，如果你加的糖份少，可以在一開始加入，如果糖份分多，建議則分次加入。

糖多糖少的區別，不僅在甜度上，也在蛋白的穩定性上。有一段時間，我不喜歡加太多的糖，結果拌的時候消泡嚴重，烤出來的蛋糕高度也沒有想像中的那麼高。糖的穩定作用還是很明確的，打出同樣體積的蛋白，用的材料越多，氣室的「壁」越厚，「壁」越厚，就越穩定，越能打發充分，越細膩。

至於為什麼分次加，主要是「加糖時，被打發的氣泡外面的液體濃度會迅速增加，形成比較強的滲透壓，容易消泡。所以，分次增加是為了減輕泡泡外液體濃度的陡然變化，加多少次都無所謂，怎麼加也無所謂。」來源：打發蛋白的一定要分三次加糖嗎？

一開始加糖可以打發的。誰告訴你不行的？

而且，因為蛋白中性發泡後打起來費勁，我擔心糖難溶，都是在濕性發泡的時候就把糖全倒下去的。btw，我是手動打蛋白的。