Notes & Theories science blog

The science and magic of breadmaking

As winter sets in, warm your senses by baking your own fresh bread. Andy Connelly guides you through the magical process that turns flour and water into heavenly food
Freshly baked bread
Use your loaf: Making bread was surely one of humankind's first chemistry experiments. Graham Turner/Guardian

When I think of bread my mind goes back to cold Saturday mornings with ice on the inside of the patio doors and cartoons blazing on the television. My dad would get up early and, after eating his porridge, would begin to make bread.

He would mix all the ingredients in a large ceramic bowl that was crystal-white on the inside and biscuit-brown on the outside. I would watch as the flour became dough and the dough grew and grew in the warm kitchen. I would linger near the oven to smell the earthy fresh bread as it baked, waiting for the treat of eating the crusty end slice of the loaf with a thick slab of butter.

I'm not saying my dad was an amazing baker, but warm bread for tea on a wintry Saturday afternoon with cheese and strawberry jam is something I will never forget. Few things are as tasty, satisfying and simple, and yet if we take a deeper look at bread we find the science of life, complex structures and the history of human development.

Archaeologists have correlated the development of human civilisations with the evolution of what is now regarded as the modern species of bread wheat. Bread is one of the oldest prepared foods, dating back to Neolithic times when lumps of dough, unleavened, were placed on hot stones in the embers of a wood fire. Bread soon became synonymous with life itself.

In the Bible it is often compared directly to life: "And Jesus said unto them, I am the bread of life. He that cometh to me shall never hunger; and he that believeth in me shall never thirst." And in the Lord's Prayer Christians ask that God "give us this day our daily bread".

In England, bread even defined the social hierarchy. "Lord" comes from the Anglo-Saxon hlaford meaning "loaf ward", the master who supplies food. "Lady" comes from hlaefdige, meaning "loaf kneader", the person whose servants produce what her husband then distributed.

Making bread was surely one of the first chemistry experiments. Finding that ground grain (a dry, loose, hard and bland substance) mixed into a rough porridge with water could be transformed into a flavourful, puffy, moist mass that was crisp on the outside, simply by placing it near a fire, was an extraordinary discovery. These flat breads can still be found in the world as the Middle Eastern lavash, the Greek pita, the American tortilla and the Indian chapatti.

Better still, if this porridge mixture was left in the open air for a few days the real science of life began. Magically, this "dough" began to rise and could then be baked into the most wonderful cloud-like substance, leavened bread.


Flour 500g
Instant active dried yeast (as specified on packet)
Warm water 300g
A quick glug of olive oil
Pinch of salt (to taste)

1. Mix flour, salt and yeast together in a large bowl. Pour in the water and start mixing with a spoon.

Look at what is happening as you mix the ingredients. The water is disappearing and the dough is forming. The shaggy mass of dough is sticking to your spoon. The mixture is slowly binding together to form a cohesive mass. If the mixture seems too wet do not add more flour, wait 10 minutes for the starch to absorb the water.

Lean over the bowl and take a good sniff. You can smell the earthy, metallic odour of flour and water with a slightly sour note from the alcohol produced by the yeast and a sweet smell from the sugars released by enzymes in the flour.

Starch (70% by weight of wheat flour) absorbs the water you have added and then enzymes digest the starch and turn some of it into sugar. These free sugars are fantastic food for yeast. In fact, you can mix the dough the day before baking, without the yeast. This releases flavours and sugars trapped in the starch, which is great for the palette and for the yeast.

Yeast metabolises sugars for energy and produces carbon dioxide gas and alcohol as by-products just as in the fermentation of beer. In fact beer can be seen as liquid bread and bread as solid beer. In case you were wondering, the alcohol burns off during baking.

C6H12O6 → 2C2H5OH + 2 CO2

In other words, one molecule of glucose sugar yields two of alcohol and two of carbon dioxide gas – the burping and sweating of yeast.

Yeast spores are ubiquitous in air and on the surface of grain, and they readily infect a moist, nutritious grain paste. However, with this recipe it is much easier to add some easy-blend yeast from a packet, which is alive but dormant, waiting for us to wake it up.

It wasn't until the investigations of Louis Pasteur some 150 years ago that we began to understand the nature of the leavening process. He, like every baker of the time, was a scientist experimenting and learning how these single-cell fungi work and how to control them.

2. Work the ingredients together into a dough and knead on a lightly floured surface for 5 minutes, or until the dough is smooth and elastic but not sticky;

As you knead your dough, turn, fold and press each time. The folding traps the air, the pressing adds mechanical energy, warming the dough slightly and aiding the formation of a network of gluten, a stretchy protein complex. The turning encourages mixing and gives a more homogeneous gluten structure. Watch the dough under your palms turn into a pliable, soft and elastic ball. Stop when the dough ceases to tear under your hands and forms a smooth, elastic surface.

Within the flour there are many long, chain-like protein molecules that are insoluble in water. When wet, and under the influence of yeast, these proteins link up end-to-end creating an extensive interconnected network of coiled proteins, the gluten. The glutinous dough is both plastic and elastic; that is, it will change its shape under pressure, yet it also resists and moves back towards its original shape when the pressure is removed. This allows the dough to expand, incorporating the carbon dioxide gas produced by the yeast, and yet resist enough to prevent the bubbles walls thinning to breaking point. Kneading the bread stretches the gluten into elastic sheets that can be filled with gas to form bubbles, giving the bread a spongy structure.

This gluten network can be stronger or weaker depending on the ingredients (such as the type of flour) and how you work the dough. Fats and oils tend to interfere with the gluten, making the gluten strands shorter, but just a little olive oil can make the dough exceptionally easy to knead, and give it a particular litheness.

The only ingredient we haven't discussed yet is the salt. If you've ever forgotten to add salt, the bread produced has a dead, rather unpleasant taste. However, it decreases yeast activity so don't add too much. The salt has been compared to the bridle, and the yeast to the whip. By judicious use of salt at the different stages you can guide and arrest fermentation.

3. Return the dough to a clean bowl and cover with an airtight plastic bag or a damp tea towel. Leave to rise in a warm place for 1-2 hours;

When I watch the dough expand I see it as a lively white cushion, growing bigger and bigger, blowing up very slowly with thousands of tiny balloons inside. As much as 80% of the volume of bread is empty space. The bubbles interrupt the network of gluten and starch granules, dividing it into millions of very thin sheets that form the bubble walls.

The carbon dioxide produced by the yeast diffuses into any tiny bubbles it encounters and enlarges them. Thus, the more bubbles produced during the preparation of a dough, the finer and more tender the resulting bread.

Yeast cannot be rushed, it must be given time. When the Israelites fled Egypt they could not tarry – they could not waste the time required for yeast to work. Their bread had not risen and so was eaten, and is eaten to this day in memory, unleavened.

The end of this period (the proving period) is signalled by a doubling of dough volume. To check that the bread has finished proving you could follow the advice of an Russian cookery book published in 1860 and place the loaf in a bucket of water. When the loaf has sufficiently risen it will rise to the top of the bucket.

Or, less courageously, you could poke the dough with your finger. If it does not spring back this means that the gluten network has been stretched to the limit of its elasticity and the dough is ready.

4. Again, knead on a lightly floured surface but this time only briefly to homogenise any remaining yeast and the air pockets that have formed

5. Shape into loafs, place in buttered tins and leave to prove for 30 minutes;

6. Bake in a preheated oven at 220C for 35-40 minutes.

Baking is the process of turning all the beautiful work you have done into a delicately chambered, crisp loaf. As the dough heats up it becomes more fluid and the gas cells expand and the dough rises (called oven spring). The main cause of oven spring is the vaporisation of alcohol and water into gases. These fill holes in the gluten network and expand the dough by as much as half its initial volume.

The oven spring stops when the crust becomes stiff and firm enough to resist and when the interior of the loaf reaches 70-80C. This is the temperature at which gluten proteins form strong cross-links and water-laden starch granules swell and set. At this point the yeast has already died and the series of transformations from grain to bread are almost complete. Now the walls can no longer stretch and so the gas pressure in the holes builds, eventually popping the walls and creating the familiar open network you see when you slice a loaf.

Legend has it that you know the loaf is finished if you hear a hollow sound when you tap the base. This means the inside is light and fluffy. More scientifically you can check with a thermometer that the centre is at just less than 100C.

Personally, I like bread with a deep brown crust, as this adds some lovely warm flavours, so I tend to cook the loaf a little longer to allow the high temperatures to caramelise sugars in the crust. Supermarket bread is rarely crusty because it tends to be under-baked; this leaves more water in the loaf, allowing less flour to be used to produce a loaf of the same weight.

7. Leave on a wire rack to cool for about 20 minutes;

8. EAT!

To perform a little chemistry test in your home take a piece of bread in your mouth and chew, keep chewing, and chewing, and a bit more. Initially you should taste your beautiful homemade bread, followed by a sweet taste which is the remaining starch being turned into sugars by an enzyme in your saliva, and then, after almost everything else has gone, a chewing gum-like mass forms in your mouth. This is gluten.

But don't do this with all the bread. Take out a large pat of butter, spread it thickly on a slice, eat and enjoy.


This article was amended on 9 June 2010. The Anglo-Saxon for "loaf ward" is "hlaford" not "halford". This has been corrected.

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