When making sourdough bread, it may happen that the dough smells like vinegar, even though it was not among the ingredients you used.
My goal with this post is to explain what causes this exciting phenomenon.
In addition to wild yeasts, sourdough contains lactic acid bacteria. These bacteria also feed on sugars, producing lactic acid and acetic acid. Lactic acid will give the bread dough a pleasantly soft, yogurt-like, or buttery aroma. Harsh acetic acid is responsible for the vinegary smell.
As a result of over-fermentation, too much acetic acid can be produced, which causes the death of the yeast in addition to the unpleasant smell. Although the strong vinegar smell of the dough is considered an error in bread making, such bread can be consumed safely.
Sourdough bread tastes good when mild lactic acid and harsh acetic acid are in the right balance. While on the subject of bread flavor, you may be interested in my article on what makes homemade bread bland.
Factors that affect the acidity of sourdough starters
1. Diversity of wild yeasts and bacteria
Making and maintaining a sourdough starter is not an easy task. The behavior of diverse wild yeast cultures is not as predictable as that of store-bought baker’s yeast, which contains only one strain, Saccharomyces cerevisiae.
Mixing water and flour is the first step in making a sourdough starter. The starch in the flour is converted into sugar by the enzymes also present in the flour. There are different wild yeast strains in the flour, on our hands, and in the air. These yeasts and the lactic acid bacteria living in symbiosis with them feed on this sugar, and the fermentation process begins.
Yeast produces carbon dioxide gas and alcohol, while lactic acid bacteria produce lactic acid and acetic acid. In addition to lactobacilli, there are small amounts of acetic acid bacteria in the sourdough starter, which also make acetic acid from the alcohol produced by the yeast. Acetic acid is the same acid that is present in vinegar.
Due to their diverse composition, some of these microbial cultures produce more acetic acid, while others make more lactic acid.
2. The type and properties of flour
In addition to the unique properties of wild yeast cultures, the type and properties of flour also affect sourdough fermentation.
The higher the ash content of the flour, the more acidic the bread will be. Higher ash content in flour means a higher mineral content and more bran in it. Flour with a lower ash content is refined to a greater extent.
According to a study published in the Institute of Food Science Technology, bread made with dark flour contained twice the concentration of acetic acid and 30-50% more lactic acid than bread made with white flour.
3. The consistency of the sourdough starter
The acidity of sourdough is influenced by the ratio of water and flour in it.
Stiffer sourdough starters made with less water are more favorable to lactic acid-producing bacteria, so the mildly acidic lactic acid will dominate.
However, a loose sourdough starter with a high water content favors acetic acid-producing bacteria, so harsh acetic acid will dominate in them.
4. Temperature also affects the acidity of the sourdough
According to the expert of the Puratos company, more acetic acid is produced in sourdough with lower water content and at a lower temperature (20-25°C/68-77°F), which is why it will typically taste more vinegary.
In a warmer environment (30-35°C/86-95°F) and in softer sourdoughs with higher water content, more lactic acid is formed, resulting in a yogurt-like taste.
5. Timing is very important
You also have to monitor the activity of the sourdough and learn to decide when it is ready to use. The ideal moment to use a sourdough starter is when it doubles in volume after the last feeding. If you let it stand for too long, the vinegar smell will intensify.
6. The amount of added sourdough starter also affects the acidity
The sourdough starter should be at least 15% of the total weight of the dough to make a mildly acidic bread.
The maximum amount of sourdough starter shouldn’t exceed 40% of the total mass of the dough. This ratio will result in a rather sour-tasting bread.
7. The effect of the proofing temperature on the acidity of bread
If you proof your bread dough in a cooler environment, the activity of the yeast slows down, and the bacteria that produce vinegary-smelling acetic acid become more active.
In bread proofed in a warmer place, the yeast is more active and the bread rises faster. The taste of such bread will be dominated by milder lactic acid. Lower bread rising temperatures favor the formation of acetic acid, and higher temperatures favor the formation of lactic acid.
Acetic acid is a byproduct of sourdough fermentation and is good in moderate amounts, but in large quantities, it can also be responsible for the bread's excessively sour smell and taste.
The vinegary smell can be prevented by paying attention to the duration and the temperature of the fermentation of the sourdough starter. Overly long fermentation can result in the production of too much acetic acid, damage yeast cells, and ruin the quality of the bread.
For further information on bread making, be sure to check out my article on the main ingredients in bread and their purpose.