|Fresh eggs straight from our backyard!|
The egg yolk and the egg white are made up of different components, so they can sometimes result in completely different products. For this reason some recipes ask you to split the eggs into whites and yolks. The egg white is made of 90% water and 10% proteins. It makes up roughly 60% of the egg’s weight. The yolk on the other hand is made out of 50% water, 1/3 fat and 1/6 proteins. The yolk also contains almost all of the vitamins and nutrients of the egg.
The protein, together with the lack of fat, gives the egg whites the ability to foam. Egg whites can hold a lot more air than any other ingredient can achieve. The fat in the yolks inhibits this foaming, so it’s best to avoid getting any egg yolks into your egg whites when you separate them (while the other way around is fine).
Especially when you have chickens yourself you'll notice a big difference between fresh eggs and old eggs. As the egg ages the egg yolk soaks up the water from the egg white resulting in a bigger yolk but also a weaker membrane. Older eggs can thus appear very watery and pour right out of their shell and are much easier to peel after boiling. Very fresh eggs however will hold together much firmer, which makes them perfect for frying or poaching. These changes do not affect the nutritional quality of the egg or it’s baking properties.
So now off to the purpose of eggs in baking. Eggs have so many purposes in baking I’m at loss at where to start! No one ingredient has this many uses. I’m sure you already know quite a few, so I’ll try to keep it short.
Think of soufflés and sponge cakes: eggs can be used as leaveners, as I already described in a post on Leaveners. Because of its ability to foam (especially those whites!) eggs are perfect natural rising agents. Before baking, you incorporate air by whisking (this process is also called ‘mechanical leavening’). During baking the water from the egg evaporates, while the elasticity of the proteins ensures the steam stays in the batter. These membranes set quickly (around 70°C/160°F), trapping the air inside before it collapses. You’ll end up with a fluffy cake-like texture and a soft crust. Eggs also provide moisture for chemical leaveners to do their work.
Eggs improve the structure of our baked goods, not only through leavening. The egg yolks will result in a denser structure with a fine crumb, whereas the whites will result in a very light, fluffy structure with a larger crumb. Eggs also provide moisture for the dough or batter and bind the ingredients together. Think of sponge cake, where eggs are the only ‘liquid’ to bind all ingredients. In sauces, like mayonnaise, salad dressings and other sauces they help emulsify the ingredients. When heated they add thickening power to custards, sauces and ice creams.
Because of the water and proteins baked goods with egg often taste dry and dry out more quickly than those without. To compensate for this, you can add extra fat. A spoon or two of milk or milk powder in cakes and breads also does wonders.
The Shiny Colour, the Flavour & All those other things
What ingredient doesn’t affect the colour and flavour of the end product? Especially in custards you will notice eggs give our baked goods a golden colour. When brushed on breads or cookies they add a lovely shine. Egg whites will give a light golden crust, while the yolks (diluted with milk or water) give a darker gold crust. As for the flavour, imagine that same custard and you’ll instantly know what I mean when I say eggs add a rich flavour to our baked goods. Especially the egg yolks (which are more than just water) add flavour to our baked goods. But there’s more! Apparently eggs can clarify soups and coffee and retard crystallization in boiled candies and frostings. (Don’t ask me the details on these!) Also, don’t forget the nutrients! Proteins, vitamins and water are essential in any diet – although baked goods should not be your main source for any of these!!
So to summon it all up: eggs consist of a yolk and a white. Both have their own uses in baking: the whites foam like mad and the yolk contains most of the colour, flavour and nutrients of the egg. The main purpose of eggs in baking is their astonishing ability to leaven our baked goods. But they also act as a moisturizer and emulsifier. They add a shiny gold colour, a rich flavour, some other crazy things and a whole bunch of nutrients (especially those proteins!). Oh, and while eggs age their structure changes – which you could totally use to your benefit!
The funny thing is I notice a lot of similarities with my other posts. Take butter: it contains fat and water. Take the yolk: it contains water and fat. While completely different ingredients, the effect of these components is the same. Perhaps I should just write Oven Info posts on the different molecules and just tell you where to find them?
I really hope you learned a thing or two and enjoyed reading this post! Next month I'll share something on flour. (I promise!!) Until then: I hope you get to enjoy the last remaining bits of summer!
Bread by Christine Ingram and Jennie Shapter
Culinate - Kitchen Chemistry
Baking 101 - Joy the Baker
Kitchen 101 - Chasing Delicious (This link includes lots of extra information, including problem-solution cases. It's something you don't want to miss out on!)
Eggs - Baking 911