HOW BAKING WORKS
I love making cakes but being an ex-scientist, I'm also a bit of a geek too, and having always had a fascination in how the world we live in works, I thought it would be interesting to have a little science lesson on how a gloopy, liquidy mass that you shove in the oven becomes a moist, fluffy birthday cake, a crusty, moreish loaf of bread or a crisp and marshmallowy meringue. Indulge me...
Everybody loves a good diagram, so instead of having to read through loads of text, take a look at the excellent infographic below taken from the Berries.com website The information is quite general applying to bread and cakes and pastries, while I have added some additional information which leans more towards cake making.
This is most noticeable in pie crusts and puff pastry where the layers of dough are separated by layers of fat. Fats can also help prevent the dough bubble walls from collapsing prematurely and so help with increasing volume and lightness.
The innovation of hydrogenating vegetable oils to make them in to a solid allowed air to be incorporated much more easily. Modern shortenings also contain nitrogen bubbles to aid leavening.
There are more than 100 different species of yeast which are microscopic single-celled fungi, related to mushrooms.
It has been used to raise breads for 6,000 years, originally being sourced from the grain surface or a piece of dough. Nowadays it's grown on molasses in fermentation tanks
The English word 'flour' originates from the Medieval word for 'flower', meaning the best part of the grain.
Most flours on sale in supermarkets contain no indication of the type of wheat they contain or their protein content.
Bread flours contain the highest proportion of gluten proteins (12-13%), followed by English plain and self-raising flours (7-10%). Self-raising flour has baking powder already added. Cake flour, which is more hard to come about in the UK contains 7-8% (you can make your own cake flour by adding corn flour to plain in the ratio of 6.3:1
Cake flour is chlorinated in the USA to bleach it, which also has the effect of making the cake finer and more velvety. There's no evidence that chlorination is dangerous, but the EU and UK consider its safety unproven and forbid its use.
Freshly milled flour needs to be oxidised so that the gluten and baking properties improve. Originally this was done naturally by leaving it out in the air. Nowadays to shorten the time vitamin C is often added.
A mixture of flour and water is called either a dough or a batter depending on the relative proportions of the two major ingredients.
The gluten network is both 'elastic' and 'plastic', meaning it changes it shape under pressure, e.g. it will expand to incorporate carbon dioxide but the bubble walls will not burst, so that the bread or cake rises and keeps its shape.
Kneading and mixing increases the strength and elasticity of the gluten network - in yeasted breads and puff pastry this is desirable but not so much in cakes and cookies
The strength of gluten network can be controlled by a number of ingredients and techniques:
type of flour
water content - more water means a less concentrated and moister dough
more stirring and kneading results in a more elastic network
salt strengthens the gluten network
sugar limits the development of gluten and tenderises the structure
fats and oils weaken gluten and tenderises
acidity, e.g. from yoghurt or buttermilk, weakens gluten network
In a chocolate cake, cocoa powder takes on the water-absorbing and structural duties of flour, therefore it's important to subtract the correct amount of the flour from the mixture to prevent the cake becoming too tough.
The word 'starch' comes from the Indo-European root meaning 'stiff'. Starch was first used to stiffen linen in the 14th century. The carbohydrate composes roughly 70% of the weight of flour.
This is structure is known as the 'crumb', while the outer surface is called the 'crust'
Chemical leavening agents are concentrated and produce CO2 much more quickly than yeast. Because cake batters can't hold gas bubbles for more than a few minutes they need this fast-acting source of CO2 rather than yeast.
Common acidic ingredients include sourdough cultures, buttermilk and yoghurt, brown sugar & molasses, chocolate and cocoa.
Baking powder contains baking soda and acidic solid crystals therefore doesn't need additional acidic components in the cake mixture for it to work. Most supermarket brands are double-acting, producing gas upon mixing the powder in to the batter, and then during the baking process.
The gas bubbles produced interrupt the gluten and starch network. The result can be that as much as 80% of the volume can be empty space!
The CO2 produced doesn't create new air bubbles, but diffuses into and enlarges the tiny bubbles that are already there produced from the initial aeration of doughs and batters from kneading, creaming butter and sugar, or whipping eggs!
Soooo, when a recipe says to whisk the butter and sugar so that it becomes light and fluffy don't skip this step - your cake won't rise as much!
Before the advent of chemical raising agents or electric whiskers you can imagine the amount of effort it must having taken to incorporate air bubbles into a cake mixture! Even with an electric whisk this stage can still take 15 minutes.
Techniques for aerating cakes:
sugar beaten into butter or other shortening and the other ingredients folded in
sugar beaten into whole eggs (Genoese), yolks only (sponge), whites (angel food cake, chiffon cake) and other ingredients folded in
all ingredients beaten together (commercial cake mixes)
none (fruit cake, spice cake)
Once the foam has formed, flour is added by gently folding it in so as not to burst the air bubbles and limit the amount of gluten formed.
The word 'egg' comes from the Indo-European root meaning 'bird'. Eggs are one of the most versatile ingredients in the baker's larder, being used for a wide variety of applications from giving taste and structure to cakes, breads, soups, pasta and drinks, making light and airy meringues or dense and creamy custards, to clarifying stocks and wine, and adding a shine to pastries.
They truly embody the chain of creation in life on this planet, with the yolk being formed from the plant material eaten by the hen, who in turn is created from the yolk, all of which is given life from the sun (the word 'yolk' comes from the Old English for 'yellow' which itself is derived from an Indo-European root meaning 'to gleam, to glimmer').
Chickens, from where we get most of the eggs used for baking, have been around for 3-4 million years, and probably became domesticated in SE Asia around 7,500 BCE
Whisking also works the same way as heating by encouraging the proteins to bond to each other and form a more solid structure (a foam).
The egg white turns from clear to opaque as a result of the large protein molecules clustering together and deflecting light rays.
Sugar is also an important leavening agent in cakes - the sharp edges of the crystals cut in to the fat or eggs as it's beaten, carrying air in to the mixture. Cakes that omit refined sugar require more chemical leavening to produce a suitably risen cake.
Sugar also interferes with the gluten formation, egg protein coagulation and the starch network and so tenderising the cake
Sugars melt into a syrup then slowly change colour from a light yellow to a dark brown depending on how long the sugar is cooked.
Baking a cake can be divided in to three parts:
Expansion, where the gases in the air cells expand and chemical leavening agents release CO2 and water vapour begins to form
Setting, during which time the egg proteins coagulate, starch granules absorb water, swell and gelate.
Browning, where batter solidification is complete and the flavour enhancing reactions on the dried outer surface.
Once the cake starts to shrink away from the tin and a toothpick comes out clean from the centre of the cake, it's done.
Named after a French physicist who described these reactions in 1910.
Maillard flavours are more meaty than caramelised ones.
Tightens the gluten network allowing it to hold more water and carbon dioxide, therefore making the dough more elastic and allowing it to expand more without tearing.
The bread is generally easier to handle and has better volume and a finer crumb.
In sourdoughs, salt limits the activity of the souring bacteria that can damage gluten.
CAKE PANS...can have an important influence on the rate and distribution of heating. Bright surfaces reflect heat in the oven and transmit heat poorly to the food they contain, resulting in a slower baking process than a dull metal pan or glass one (as much as 20%).
COOLING TIME....after a cake has come out of the oven its structure is quite delicate and should be allowed to cool before being taking out of the pan, otherwise, as well as burning your fingers, you could find it breaking apart in your hands.
Gradually the starch molecules will settle back into close, organised association with each other. Cakes that have less fat and flour and are aerated with eggs, e.g. angel cake, can shrink back down considerably as the air bubbles the egg proteins surround contract down, therefore you;ll see the recipe saying to suspend the cake upside down while it cools (don't be scared to do this ;-)).