Bun in the oven!

What gives bread it's characteristic fluffy texture? Why does it rise up? Why do you need to prove the dough before baking? What happens during the all important baking step? And most importantly, where does that all important bread smell come from? How do supermarkets make their bakery aisle smell so inviting?

It's bread week here on Chemystified and I shall be having a go at baking my own loaf.

My loaf.
Recipe courtesy of the queen of baking Mary Berry.

Like many who watch the Great British Bake Off will know some of their creations are masterpieces of art. I am a firm believer that cooking is a science and that baking is just chemistry in action that we can enjoy with our eyes as well as our taste buds.

Figgy olive oil and sesame challah
Credit: Sarah R

Without trying to sound too much like a recipe book, we'll start with what goes into a basic loaf of bread. Into our metaphorical mixing bowl we will put:

Ingredients for the farmhouse loaf

• Flour
• Yeast
• Salt
• Water
• Butter

I used the farmhouse loaf recipe from Mary Berry's complete cookbook. Our well used family copy featured to the left.

Each of these ingredients brings something to the table with regards the chemistry going on inside the dough, and like the salt doesn't just add to the flavour of our final product.

Flour Power
Starting with the flour. This ingredient makes up a majority of the stuff you put into your bake and the type of flour you are using with vary between breads: the standard white loaf requires a mixture of white and bread flour whereas cornbread, like the name implies, is made with cornmeal. Bread flour has a higher gluten content that white flour and so leads to a denser bake.

Gluten is the key part of flour that gives the bread dough it characteristic springy texture. Gluten is a mixture of two proteins and upon mixing with water the starch in the flour surrounds the protein. Kneading the dough establishes a gluten structure or network. This combined with the yeast, gives rise to the light, fluffy bread texture we know and love.

Leavening or Raising Agents

Yeast in action
Image: mystuart (on and off), Flickr

Leavening agent is just the fancy term for the ingredient that makes the bread rise. Yeast is a fungus which is commonly used as a leavening agent in breads. Yeast comes in two form: live or dried yeast. Dried yeast has the advantage over live that it will always be in your cupboard ready to go and grow... Live yeast need a little bit more looking after.

Once combined with flour and water the yeast get busy fermenting and respiring. The yeast convert sugars, sourced from starches present in the flour, into carbon dioxide . The carbon dioxide gas bubbles get trapped in the gluten structure which helps the dough to rise. As the dough expands, the gluten molecules uncoil and there is increased inter-molecular and hydrogen bonding making the dough stronger.

Baking powder and bicarbonate of soda can also be used as raising agents where a smaller rise is required. For example in a flat bread.

Salt
Salt is added to dough not only for its flavouring properties. The presence of sodium chloride (or common table salt) promotes the aggregation of proteins and leads to a stronger, less sticky dough.

Time to Rise: Watch It Grow

My dough after proofing
for around 2 hours.

Following the combination of ingredients and kneading of the dough, it must be left to proof. During this time yeast is fermenting, which helps develop the flavour of the bread and the dough is rising. The longer you leave the dough to rise, the bigger the loaf will be, however the dough won't go on rising forever. Yeast is limited by the finite resources for fermentation in the flour.

Chemical reactions also occur at this stage between natural oxidants. Links between the protein chains repeatedly break and reform, allowing the dough the stretch without losing its structure.

Baking: The Ultimate Chemical Reaction
It is during baking that the bread undergoes the greatest change. It goes from a soft and squishy dough to a crumby, crunchy loaf.

Because the yeast is actually a living organism, when the bread enters the oven they are all denatured or killed due to the heat. This stops the loaf rising once its baked.

There are various stages to the baking process, The first of which is reliant on the water in the dough evaporating and steam produced. The steam, being a better conductor of heat than the dough itself, efficiently heats the dough throughout, center to the forming crust. The evolution of steam also causes the loaf to rise further. This is called the oven spring and happens within the first ten minutes of baking.

The steam is then be vented from the oven, allowing for the formation of the crust and the drying out of the bread crumb. Too much steam and the crust won't form properly. Too much heat and one side of the bread may burn before the crumb dehydrates.

The outside of the loaf cooks quicker than the outside, owing to the poor heat transfer of the dough. As this is the first part of the bread to cook, you could liken it to cooking meat, when you sear the outside. The starches in the outer part of the dough are broken down into simple sugars which are caramelized.

Bread Vs. Biscuit
Bread and biscuit or cookie recipes are very similar, bread is savoury and biscuits are sweet. There is a difference in the way that they are baked however. Bread is cooked at a much higher temperature which means that as well as starches breaking apart, the gluten protein is also broken down into smaller amino acids, which recombine with other compound in the bread dough. This reaction is called the Maillard reaction and owes to the golden colour we associate with the baked bread.

So...  biscuits = sugars caramelizing and bread = sugars caramelizing + Maillard reaction

The combination of the two processes leads to the thicker crust of bread compared to that of a biscuit.

The Smell Is Killing Me! In a Good Way!

My loaf cooling.

Bread had a very distinctive smell and it permeates a room best when its warm. So when you take your loaf out of the oven the vultures will descend, ready to munch away and nothing beats a still warm from the oven slice of bread and butter. But back to that aroma.

More than 540 volatile compounds have been identified as being present in bread, but only sixteen contribute to the smell. Of these fifteen, 2-acetyl-1-pyroline contributes most to the smell of white bread crust. [I. Cho, D. Peterson, Food Sci. Biotechnol., 2010, 19(3), p575-582]

2-acetyl-1-pyroline
Compound that contributes most to white bread smell

It would appear that goodness was the death of my bread, they are both gone and I only made them yesterday...  So go on, I challenge you to bake your own bread and see how long it lasts! Share a picture of you bake.  

Ready. Set. Bake!