---
title: 'The science of sourdough bread'
source: 'https://youtube.com/watch?v=ipBonoCkNk8'
video_id: 'ipBonoCkNk8'
date: 2026-06-30
duration_sec: 177
---

# The science of sourdough bread

> Source: [The science of sourdough bread](https://youtube.com/watch?v=ipBonoCkNk8)

## Summary

Sourdough bread uses a wild starter instead of commercial baker's yeast, which introduces diverse yeast strains and lactobacillus bacteria that create unique flavors and textures. The process involves growing a culture from wild yeast, feeding it daily, and using a large proportion of it in the dough to achieve a slow fermentation that enhances digestibility, flavor, and structure.

### Key Points

- **Sourdough vs. Normal Bread** [0:00] — Sourdough uses a wild starter instead of a single strain of mass-produced baker's yeast, leading to diverse yeast types and flavors.
- **Growing Wild Yeast** [0:33] — Wild yeast settles on grain berries; when flour is mixed with water, the yeast feeds on sugars, producing alcohol and CO2 gas. Bubbles appear after about five days, indicating yeast growth.
- **Role of Lactobacillus** [0:58] — Lactobacillus bacteria grow alongside yeast, producing lactic acid that gives sourdough its tangy flavor and name.
- **Maintaining the Starter** [1:15] — A small portion of the starter is fed daily with fresh flour and water to keep it active indefinitely.
- **Dough Composition and Mixing** [1:34] — 30% of the dough is the culture, mixed with fresh flour and water. Mixing develops proteins that trap gas, creating a chewy texture.
- **Proving and Shaping** [1:55] — The dough proves until doubled in size, which takes longer than commercial bread. Gentle shaping preserves gas pockets, and the dough is placed in floured baskets to form the crust.
- **Benefits of Sourdough** [2:37] — The long production time makes sourdough more digestible, flavorful, and textured, with a better crust and ability to spring back when squashed.

### Conclusion

Sourdough's unique flavor, texture, and digestibility come from its slow fermentation using a wild starter, which requires daily care and patience but yields superior bread.

## Transcript

Sourdough differs from normal bread, as you 
might call it, by the fact that we're using a  
wild starter instead of baker's yeast. So baker's 
yeast is one single strain of wild yeast which is  
mass-produced, to create this milky substance 
of yeast that's then compressed into a block,  
and that's trillions of cells which means you 
can make bread much much quicker without any time  
of developing that dough and growing 
that yeast, it's already been grown.  
With a sourdough you don't know what type 
of yeast you're going to get in your bread,  
so you get lots of different 
yeast creating different flavours.  
What you do with the wild yeast is you grow it 
from a small culture. Wild yeast settles on the  
outside of a grain berry, as soon as that's 
ground into flour and you add water to it,  
it begins to feed on the sugars. When it feeds on 
the sugars it creates alcohol and it creates gas,  
the gas being CO2. In five days time you'll start 
to see some bubbles popping up into the culture.  
Those bubbles are the first sign that the yeast is 
beginning to take a hold and grow. Lactobacillus  
is basically a good bacteria that grows alongside 
the yeast, that's what gives sourdough its name.  
It creates lactic acid, it gets sharper and 
sharper. It gives it it's flavour so it's a  
very important thing that the two grow together. 
In the morning when you come into the bakery it  
smells more like a brewery because of all the 
starters fermenting creating alcohol and gas.  
We then take a little bit of that, feed it with 
fresh flour and water and by the next day it's  
bubbling away like mad and that is your culture. 
Once you've created that culture, you just have  
to keep feeding it every day, keep a little bit 
back and feed it, and that will last you forever,  
as long as you remember to feed it every day. 30% 
of the dough is made up of the culture, unlike  
a small amount of yeast you would add to bread. 
We're adding 30% of this culture, to fresh flour  
and water to make the dough. The dough is then 
mixed, to allow the proteins to join together.  
The proteins are what trap the gas. So you've got 
two different types of protein that create this  
chewy gum-like texture to the dough that trap the 
gas produced by the yeast. We allow it to prove to  
double its size. This takes quite a long time when 
making sourdough because you're growing yeast.  
So once the dough's developed or 
'proved' we've got this massive  
marshmallow of dough so we're then gently 
shaping it because we don't want to lose  
all those pockets of gas. It's taking a long 
time for that wild yeast to create that gas  
we don't want to knock it out. So we gently shape 
it, round it up. We then put that shaped dough  
floured into baskets. That helps to create 
the crust around the outside of the bread,  
holding it together and it allows it to 
rise within the basket so we keep the shape.  
The proteins are trapping the gas and create 
those big holes synonymous with sourdough. We  
then turn it out onto wooden peels, score it, and 
then load it straight onto the stone in the oven.  
Sourdough has something in it that normal 
bread doesn't have and that's a lot of time  
in its production, which makes it more 
digestible, it gives it more flavour,  
more texture, you can squash it flat, it will 
bounce back. It gives it a better crust as well.  
Flavour is the biggest thing though, it 
completely changes the flavour of the bread.