How to (scientifically) make bread.
Bread. Simple, yet so complex.
Bread has always fascinated me from a young age. My mom would often prepare our homemade pizza dough hours in advance. I’m still in awe after I see her creation double in size. To curb my restless impatience, my mom would tell 10 y/o me:
“The dough has to proof, and the yeast needs to activate”
As a kid waiting for pizza, I didn’t want to let the dough rest. I wanted pizza right away.
I now understand why patience is key to bread making.
Here’s how you can make your own bread, in a few simple (yet complex) steps.
Step 1: Gather your Ingredients
You will need:
- Flour
- Water
- Yeast
- Salt
Let’s go into what role they play in the process.
Flour
All wheat flours contain two important proteins: gliadin and glutenin. In the presence of water, these proteins bond together and create a network of proteins collectively called gluten. Flour also contains amylase which is necessary for starch to break down simple sugars in a process called autolyse.
Water
Water is vital to hydrate our dry ingredients and activate the proteins within flour. Food scientists measure the amount of water that is used for the growth of microorganisms, as well as enzyme and chemical activity through a measure called water activity (aW). Essentially, water activity is a measure of the water that is available to be converted to vapor. There is a general correlation of the moisture content of food with its water activity.
Yeast
Yeast is a fungus that eats sugar and produces carbon dioxide and ethanol as waste. It’s the key player when it comes to bread making and alcohol fermentation for wines and beers.
Salt
Sodium and chloride ions are essential for the convergence of protein chains (for a stronger more elastic dough). Salt slows enzyme activity as well as the rate of fermentation — but it strengthens the gluten.
Step 2: Knead, Knead, Knead!
Gluten development
It’s time to mix our ingredients. Autolyse is the artisan bread method developed in the 90s by the french scientist, Raymond Calvel. It involves mixing flour and water to create gluten. Once the proteins are hydrated they begin to stick together through the formation of chemical bonds.These chemical bonds are called disulfide cross-links and with continued mixing, a network of chemically linked proteins is formed. When the dough is kneaded, a viscoelastic matrix is created. Glutenin and gliadin would not be as elastic on their own. Kneading and constant mixing of the dough is crucial in the beginning stages in order to create that network and reach the optimal elasticity. Gluten becomes stronger as more bonds are formed between the proteins. The more you knead, the more gluten you have, which will allow for more carbon dioxide to be trapped within the network. This is significant because the carbon dioxide is what inflates the dough as it rests and bakes. Below are a series of scanning electron micrographs of different stages of gluten development from the German journal Zeitschrift fur Lebensmittel-Untersuchung und-Forschung (1990).
Step 3: Proof
It’s now time to let our dough “proof”. The proofing process refers to main fermentation stage of the dough, where our yeast will activate and the dough will rise.
The yeast eats the sugars provided from the flour, metabolizes them, and the waste products are what give rise to bread’s distinct flavour and texture. The yeast cells undergo glycolysis, a process that breaks down glucose in order to create pyruvate, NADH as well as ATP. Check out my past article here if you’d like to dive deeper into that pathway. After glycolysis, the yeast cell chooses to carry out ethanol fermentation.
Ethanol Fermentation
- In glycolysis, glucose is converted to 2 molecules of pyruvate and at the same time, 2 molecules of NAD+ are reduced to NADH
- Pyruvate is then converted to acetaldehyde (2 carbon dioxide is released in this reaction)
- Pyruvate has a carboxyl group that is removed by pyruvate decarboxylase. The carboxyl group , in its shape, is carbon dioxide — this is how carbon dioxide is released
- What is left over of the pyruvate is now acetaldehyde. The acetaldehyde can be reduced (meaning it can gain electrons) and it gains a hydride anion.
- Acetaldehyde is converted into ethanol after being reduced. During this process, NADH is oxidized back into NAD+ in order for glycolysis to occur again.
Air Pockets!
How do those bubbles get there? As the yeast ferments and produces carbon dioxide as the by-product, the carbon dioxide needs to get trapped somewhere. As the bread proofs, the reaction of converting pyruvate to ethanol occurs slowly (which is why the best breads end up being proofed for hours or even overnight). The carbon dioxide is trapped between the network of gluten that is created during the kneading process.
Step 4: Bake
With an increase in temperature, the rate of reaction is increased as well. The yeast continues to produce carbon dioxide as a by-product and due to the high heat in the oven. The energy transfer causes the carbon dioxide gas particles to expand within their container (gluten).
The thermal death point for yeast cells is 130°F–140°F. Most bread is baked when the internal temperature reaches 200F — at this point the yeast is dead. Note, most gluten-free breads use a larger quantity of yeast, which is why they are usually cooked at higher temperatures. As for ethanol, most of the ethanol is baked off, but some breads can still contain trace amounts of alcohol!
Maillard-Hodge Reaction
The Maillard reaction is used in creating important flavours in cooking. The reaction is well recognized for creating the flavors of baked bread, seared meats, roasted coffee beans and dark beer. The reaction was coined after the French scientist Louis-Camille Maillard who published his research into the reaction of amino acids with sugars in 1912. He discovered that brown colours were created when amino acids were heated with simple sugars like glucose. This browning is “non-enzymatic browning”. Enzymatic browning is what happens when apple slices or potatoes turn brown due to natural enzymes within the cells.
It’s fascinating to look through the scientific perspective on how things come to be in our day to day lives. Humans are the best of manipulators and the greatest of inventions have followed and taken advantage of processes and systems occurring naturally.
If you enjoyed this article and would like to go deeper into food science and the process of fermentation, check out this awesome lecture done at Harvard University.
I’m super interested in how metabolic pathways make up the world around us. Understanding the human metabolome will unlock a new age of medicine and increasing healthspan. Connect with me on Linkedin, and let’s talk about the future of Metabolomics!
