The Science and Magic of Sourdough Bread

Words, recipe and images by Charlene Trist

At its most elementary, bread is merely flour, water, yeast and salt; yet if we take a deeper look, we find complex chemical transformations that turn lumps of wet dough into a food that throughout the ages has become synonymous with life itself. By no means am I an expert baker, however since familiarising myself with the basic chemical, physical and functional properties of sourdough breadmaking, I have been able to turn out light, aromatic and rustic looking loaves that hold up against many bakeries, and I am sure you will too.

Tools - what you will need to get started

1 x 1 litre capacity Mason jar or glass storage container

1 x large mixing bowl

1 x plastic or metal bench scraper

1 x set of measuring spoons

1 x set of measuring cups

1 x measuring jug

1 x sharp knife for scoring

1 x kitchen scale

1 x sheet pan

1 x damp tea towel

A mixer or food processor may be useful but not essential. In my opinion, kneading by hand is the best way to determine if the dough needs any adjustment with flour or water and is the most therapeutic part of breadmaking.

Other tools which are useful but not essential are a baking stone, ceramic baking cloche or Dutch oven, razor blade, a timer and proofing cloths.

Sourdough and wild yeasts

Sourdough breads get their name from the fact that both the dough and bread are acidic. The acidity, along with other distinctive flavour components, is produced by bacteria that grow in the dough along with various yeasts. The leavening for this kind of bread begins as a “wild” starter, a mixture of whatever microbes happened to be on the grain and in the air and other ingredients when flour was mixed with water. The mixture of yeasts and bacteria is then perpetuated by saving a portion of the dough to leaven the next batch of bread. The bacteria and yeast consume starch and produce gas for the bread to rise. This is the process of fermentation and it makes the food more nutritious, flavoursome and digestible.

A healthy and active sourdough starter contains two types of organisms – yeast and lactic-acid bacteria and takes at least five to seven days to make. You know you have a good balance of yeast and bacteria when the starter is full of bubbles and has the characteristic smell of fermentation.

Sourdough starters are often referred to as a ‘hydration’ percentage for example 100% hydration sourdough starter. The percentage indicates the hydration of the flour in the starter. As my recipe requires equal quantities (by weight) of both water and flour, it is a 100% hydration starter. The hydration of a starter not only affects its consistency but also how quickly it will ferment. The more hydrated the starter, the quicker it will ferment and the more feeding it will require.

Sourdough Starter Recipe

Ingredients:

150g high protein bread flour

150mls warm filtered or previously boiled water

Method:

Day 1 -2

150g flour + 150g water, mix, stand for 48 hours

Day 3:

1st feeding. 150g starter + 150g flour + 150g water, stand for 24 hours

Day 4:

2nd feeding. 150g starter + 150 flour + 150g water, stand for 24 hours

Day 5:

3rd feeding. 150g starter + 150 flour + 150g water, stand for 24 hours. By now your starter should have doubled in size. If it hasn’t, continue to feed every 12 hours until it does.

Day 6:

4th feeding. 150g starter + 150 flour + 150g water, stand for 24 hours

Day 7:

Use the active starter OR store at room temperature and continue with daily feedings. If you don’t intend to bake daily, store your starter in the fridge and feed once each week.

Sourdough bread recipe

Making bread must be one of humanities first chemistry experiments. What an extraordinary discovery it must have been to realise that a porridge of dry ground grain and water could be transformed into a fluffy, flavourful and filling food product with a soft moist interior and a crisp exterior just by leaving the raw dough in the open air for a few days and then simply placing it by a fire.

Ingredients

150g active sourdough starter

400 high protein unbleached bakers flour

100g wholemeal flour

12g fine sea salt flakes

630g warm water

Method

Combining your ingredients

Mix sourdough starter, flour, salt, and water together in a large bowl. Use your hands or a wooden spoon to combine.

Take notice of what is happening has you mix the ingredients. The water is being absorbed by the flour and the dough is forming. Slowly, the mixture is binding together to form a cohesive mass. Wait 30 minutes for the starch to absorb all the water. If you take a good sniff, you will notice that the mixture smells earthy and sweet.

Stretch and Fold

The key to making good strong bread is the development of gluten. Gluten is a mixture of two proteins called glutenin and gliaden that can’t dissolve in water, but do form associations with water molecules and with each other. When hydrated and with the assistance of the fermentation process, these proteins link up end-to-end to form super-chains a few hundred glutenins long and form temporary bonds with similar stretches of neighbouring gluten proteins, resulting in an extensive interconnected network of proteins, the gluten.

To strengthen the dough and make it more buoyant, complete four sets of folds using the technique demonstrated in this link, resting the dough between each one for 30 minutes.

If you use this technique, you will gradually feel the dough strengthen, becoming a soft and supple ball. You will know when the dough is ready when it can pass the windowpane test. Stretch the dough into a translucent thin membrane (i.e., a windowpane) and hold it up to a light. If you can stretch the dough and see through it, without the dough breaking, a sufficient amount of strong gluten strands have formed.

The dough has been kneaded properly when you can stretch the dough and see through it like a windowpane

The dough is now ready to form lots of gas bubbles, giving it the spongy texture for which sourdough is renown while it rests in the refrigerator for at least six hours or overnight.

While your dough is resting, the yeast introduced in the starter mixture is metabolising sugars in the starch for energy and expelling carbon-dioxide gas that fill the dough with bubbles, giving it volume and making the bread light and tender. The yeasts also release a number of chemicals that affect the dough consistency, thus strengthening the gluten and improving the doughs elasticity resulting in larger holes in the crumb – a distinguishing feature of a good sourdough bread.

Shaping

After the dough has risen overnight and roughly doubled in volume, it will need to be shaped before its second proofing at room temperature. Shape the dough by gently patting the dough into a rectangle then bring all four corners together in the centre. Squeeze the corners to seal them and tighten the skin of the dough by gently rolling the dough on the counter to create surface tension as in the technique demonstrated here:

Proofing

Dust a proofing basket or a tea towel lined mixing bowl with wheat flour, rice flour or semolina. Transfer the dough to the prepared proofing basket, seam side up, cover with a damp cloth and let it rise at room temperature for a further two hours. This is called proofing because it proves that the dough is still alive.

Scoring

It is important to score the bread with a sharp knife or razor blade just before baking to release some of the trapped gas and to control how the bread rises while baking. Now is a great time to take another sniff and notice the distinct change in aroma. What was once earthy and sweet, is now sour and musty.

Baking

Bake at 230°C for 40 minutes or until the desired level of browning/crust caramelisation (the browning of sugar due to heat) is achieved.

Baking is an important stage in breadmaking because it implies many physical and chemical changes such as evaporation of water, formation of crumb structure, volume expansion protein denaturation (the undoing of proteins natural structure), and starch gelatinisation (the disruption of molecular orders within the starch granule manifesting in irreversible changes in the starches properties).

Until the middle of the 19th century, bread was baked in clay, stone, or brick wood fired ovens which were ideal for bread baking as they retained a large amount of heat energy. As the dough warms, it releases steam, which fills the closed chamber and creates a rapid expansion of the gas cells resulting in a larger and lighter loaf and a glossy crust.

Steam can be applied in domestic ovens at the beginning of the baking process by spraying some water or dropping ice cubes on the oven floor or by pouring a cup of water to a pre-heated baking dish while it and your loaf is in the oven (if you do this method, take care to not burn yourself).

Alternatively, you could replicate the steaming process of a wood fired oven by baking the loaf in a pre-heated bread cloche or Dutch oven as I have done, Just remove the lid after the first 20 minutes of baking.

Resting

Remove your loaf from the oven and allow it to cool down. As the temperature declines, the starch granules firm up and the bread can then be sliced without tearing.