Oxidation and over-oxidation in bread dough is likely a topic that doesn’t get mentioned enough by bakers. To understand its importance, here’s is an experience I had last year:
I had tried to make a spectacular “super bread”. I’d mixed it “hard”, bulk fermented it “long”, and gave it a “nice”, extended rise. I thought it would be a showstopping loaf. But in reality, the dough lost its strength and flavour. I still remember my bitter disappointment when it came out of the banneton and collapsed.
I now know that it did this because of over-oxidation. So what is the truth about oxygen in bread, is oxygen required and how to prevent over-oxidation? Let’s take a look.
The 7 Things You’re (Probably) Doing Wrong!
Improve Your Baking Skills With My Free Email Course- Sign Up Here!
Hey there! Some links on this page are affiliate links which means that, if you choose to make a purchase, I may earn a small commission at no extra cost to you. I greatly appreciate your support and I hope you enjoy the article!
What is oxidation in bread dough?
When flour is in contact with air, it absorbs oxygen. The amount of oxygen absorbed increases when the dough is kneaded. The dough uses the oxygen in the dough to strengthen the dough structure and supply the yeast. It can also have a detrimental effect on the dough.
Sometimes dough oxidation is called oxygenation and dough with too much oxygen is known as over-oxygenated. Looking through scientific papers it seems that there is a fine line between both processes, but oxidation is the correct term.
How oxygen benefits bread dough structure
oxidation makes bread dough stronger. As gluten molecules are oxidated, sulfhydryl groups in some amino acids are oxidized to produce disulfide bonds. These contribute to the crosslinking of the gluten which produces an enhanced gluten structure. This makes the dough easier to shape and rise in a uniform shape.
How oxygen benefits the yeast
Yeast has two methods for making carbon dioxide gas in bread making. It can either operate through aerobic respiration or anaerobic respiration. Without the presence of oxygen, fermentation begins. The dough fermentation process is much talked about as it produces carbon dioxide and ethanol alongside lactic acids and facilitates the growth of more organic acid bacteria. But respiration is just as important. When the yeast undergoes cellular respiration it multiplies and produces CO2, without any ethanol or organic acids.
Aerobic respiration requires oxygen. As the yeast exerts its supply of readily available oxygen it changes its mode of operation and anaerobic respiration begins.
Aerobic respiration vs anaerobic respiration in bread
Aerobic respiration is best for lighter tasting bread that has a short rise. Aerobic respiration releases more ATP molecules which provide energy to make the dough rise quicker. This makes a lighter tasting bread.
Because of the benefits of organic acids and ethanol provided by anaerobic respiration, it is favoured in flavorful artisan bread styles. These extra components act as natural dough conditioners and flavour enhancers to make a more interesting loaf that keeps fresh for longer.
The tricky task for home bakers is to not sit on the fence! You either want to incorporate a lot of oxygen and rise the bread quickly or a longer rise for a more fermented flavour.
When making bread quickly, oxidation is our friend. This is especially true when high-intensity industrial mixers are used. But, for long-fermented bread, it becomes a problem.
If you want to advance the flavour of a quickly risen bread you should look to preferment your flour.
What is the issue with over-oxidation in bread dough?
When too much oxygen is incorporated into the dough it destroys the flavour and appearance of the bread. The yellow/creamy lipids in the flour are the carotene pigments called carotenoids. As oxygen is added they become damaged and as the dough becomes over-oxidated, they turn a pure white colour. This represents damaged carotenoids and that the minerals they contain have been washed away.
Not only does over-oxidation wash away colour and minerals it also removes much of the bread-like flavour. The flavour that remains after baking will be bitter
How to tell if dough is over-oxidated
The best way to see if there is too much oxygen is by looking at the colour of the crumb. If it is white and not aromatic there was too much exposure. Another thing to observe is the crumb. Too much oxygen can produce an overly soft and potentially crumb. You will also notice structure
The causes of over-oxidation in bread dough
Dough absorbs a considerable amount of oxygen as it is kneaded. Oxygen continues to be absorbed as the dough sits during the first and second rise. Long fermentation after intensive mixing is the main cause of over-oxidation. Yet there are many causes of oxidation in bread dough:
- Long mixing times
- Intense mixing
- Mixing the dough between 26-27C (75-77F)
- Excessive bulk fermentation/proofing
- Delaying the addition of salt until the end of mixing
How to prevent over-oxidation in bread
If a long mixing time is used, the bulk fermentation must be reduced to prevent over oxidation. It’s also a good idea to reduce the amount of oxygen that can come in contact with the dough. Little things such as using small containers for bulk fermentation and using a lid to cover dough resting containers make a big difference.
How to prevent over-oxidation when mixing
Incorporating too much oxygen is common where intense mixing is used. oxidation is prevented in some commercial bakeries by using specialist mixers that prevent oxygen from entering the dough. They use these mixers alongside adding an antioxidant such as ascorbic acid.
Ascorbic acid can be used to increase the amount of oxygen in the dough for home baking. But in specialist industrial mixers, ascorbic acid can also be used as an anti-oxidant. This allows longer fermentation times to be achieved.
Over-oxidation can also occur when poor quality stand mixers are used. Some won’t develop the gluten effectively so many home bakers increase the kneading time above 15 minutes. A lot of oxygen is still incorporated though so it is best to mix for less and increase the bulk fermentation time or knead by hand and add a small amount of ascorbic acid if you wish to make a quick bread.
How to make a quick-bread
When preparing soft-crumbed bread, a short (or zero) bulk fermentation should follow intense mixing. Mixing times will be 2-3 minutes at slow speed and 5-7 minutes at fast speed. Ascorbic acid can be added to enhance oxygen intake.
This method allows the dough to benefit from a strong gluten structure and receive big gains in the oven spring. This is achieved without risking over oxidation or the yeast running out of available sugars.
Is oxidation in dough the same as oxidation in flour?
Typically flour is stored for 3-4 weeks before it can be used. This ageing process allows the flour to absorb oxygen which matures the protein. The process of flour oxidation works similarly to dough oxidation but occurs at different stages.
It is common for flour mills nowadays to add an oxidizing agent such as ascorbic acid to fresh flour during milling. This speeds up the ageing of the flour so it can be packed and sold straight away. This removes storage and infrastructure costs without affecting the quality of the dough.
Does dough need oxygen to rise?
Oxygen is not essential for the yeast to produce gas and rise. Incorporating oxygen into the dough is very beneficial for quickly risen bread. For a longer fermented dough, the kneading duration is best kept short and slower to reduce oxygen intake.
Frequently asked questions on bread oxidation
Does sourdough starter need oxygen?
A sourdough starter should be kept loosely covered but this isn’t due to the starter needing some oxygen. A sourdough levain does not need oxygen to ferment. The lid is kept loose so that carbon dioxide produced during fermentation can be released. If securely fastened it can create a vacuum which slows down growth or lead to the jar exploding!
Why does flour contain ascorbic acid?
Ascorbic acid is a common ingredient listed on flour bag labels. It acts as an oxidizing agent to mature the flour quickly. The use of ascorbic acid reduces the cost of storing the flour without altering its quality.
Is bread making anaerobic?
Both types of respiration are used during the bread making process. Aerobic respiration occurs at the early stages of gas production and is desired in quick-breads. Anaerobic respiration leads to fermentation and is the prevailing function of the yeast in longer proofed bread.