Mechanical cake

Last year [= last week] I was writing about baking powder. Even as I wrote ". . .there are two ways of getting loft into cakes - biological and chemical . . ." I knew I was ignoring part of the cakiverse. So here I am making up for slighting the physical / mechanical ways of creating foamy deliciousness. During my expensive education, I tried a few things once and then moved on. 

• I was in a play that had a morris dancing scene; 
• but not the other Beecham thing(*); 
• I made a cheese soufflé; 
• I rode a donkey . . . for 15 seconds
  
• I went pillion on a motorcycle . . . for 15 minutes
  

You can tell I've lived a very exciting life; but the only event relevant to this post is the soufflé, which derives its light airiness from beating egg whites to a foam and folding that gloop gently into the other ingredients just before baking - pre-heat oven, or the confection will collapse.

A similar procedure is key to making meringues. The egg whites are separated from the yolk and whisked up into a foam. The bubbles of the foam are stabilized by the presence of protein - albumins and others - dissolved in the water. It is possible to over-beat the foam so that the matrix collapses, sometimes even before cooking starts. The whipping can increase the volume by as much as 8x and cooks like to achieve this maximum, even if they're not in the commercial business of selling air to punters. Various 'fixes' have been identified as either increasing the volume or, more relevantly, stabilizing the foam until the proteins are set by cooking. I am channeling On Food and Cooking by Harold McGee here [and prev].

• Don't use a plastic bowl: it is hard-to-impossible to clean oils from plastic. Oils and fats prevent the egg-white proteins making the crucial interface between air and water.
• rigorously exclude egg-yolk: lecithins are complex fatty molecules which are even more effective than sunflower oil or residual butter at elbowing into the molecular edge of the bubbles and causing collapse.
  
• salt is ionic and will change the shape of albumin and lower its foam making capabilities - if you must add salt to taste, do so at the last moment
• also add sugar [folding in] after the egg whites are proper peaky.
  
• a pinch of cream of tartar [tartaric acid as in baking powder prev] will lower the pH from 9 to ~8 and this seems to enhance the foaminess and stability
• it has long been asserted that a copper pan is a miracle-worker for meringues and there is some scientific evidence that copper ions help prevent over-beating collapse by stabilizing the foam
  
• before your eyes evidence for bowl effects
  

So there is a little chemistry in making great meringues, but it's mainly elbow work [or Kenwood Chef for wimps].

Victoria sponges are related. Cream butter and sugar till it turns white [ie gorra lorra air in], in a separate bowl whisk the eggs so that they also have a lot of incorporated air. Throw them together then g e n t l y fold in sufficient flour; taking care not to work all the air out by over stirring. Very similar in principle to a soufflé, as both rely on beating to create bubbles in a foam and ultimately in the finished product. You'd be surprised by strawberry jam and clotted cream in a soufflé, though.

footnotes
*Sir Thomas Beecham once said "In this life try everything once, except morris-dancing and incest".