Factors That Affect Sourdough

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Making bread is a craft that dates back to ancient times and has been a staple for many cultures. The bread at this time was leavened with natural yeast until baker’s yeast was developed for industrial production of bread products. Although we can find this commercial yeast in almost any grocery store, many people prefer the taste and texture of sourdough bread leavened with natural yeast.

Sourdough starters begin as a mixture of flour and water which serves as a home to various forms of yeast and bacteria. If given optimal environment, feedings, and time it will produce a bubbly, active starter ready to leaven dough. If you are working on beginning a sourdough starter, it may help to better understand the factors that can affect the growth of microorganisms in your starter.


The different types of flour are much like the different types of soil you can choose from to grow your garden. Each one provides various nutrients and properties to your starter. The type of flour used can impact your starter’s ability to leaven as well as the flavor profile. Flour not only provides nutrients to your starter, but is also a natural source of yeast. Research is still developing on understanding how the types of flour relate to the microorganisms introduced and the flavor profiles. Different types of flour you can use include rye flour, whole wheat flour, and unbleached all purpose flour. Whole grain flours contain fiber, starches, proteins, and other properties that aren’t found in white flour.


The first concept of time is the age of the starter. A mature starter is likely going to have a strong yeast culture and may also have stronger leavening properties. Secondly, the amount of time between feedings is another crucial factor. Re-feeding, as it is called, is when you discard excess starter and adding fresh water and flour to the remaining starter in the container. When given an optimal range of feedings, the sourdough starter is more likely to higher diversity and fermentation.


Starters are much like people in that they like to remain in a warm temperature, but not too warm. They are most active around 70 degrees Fahrenheit. You can store them in the refrigerator, but the activity will slow down significantly in cooler temperatures. If held at too high a temperature, you may overheat your starter and kill the yeast.


The moisture level of sourdough starter is an important factor that affects the activity and the microorganisms in the starter. Sourdough starter recipes should include a ratio of flour and water to use.


There will be bacteria present in starters that come from the environment, container, flour, and water used that helps it form a unique microbiome. They are present in the beginning and are added continuously as a starter grows and is refreshed with feedings.


Yeasts are a single celled microorganism from the fungi family. Starters obtain yeast from the flour used and the environment which also helps it form a unique microbiome. The yeast in a starter produces carbon dioxide which makes it very useful in leavening dough. These tiny organisms can give each starter its own unique flavor. They also have an affect on the activity of bacteria. Yeast may overtake the bacteria right away or it may take five to seven days.

Unwanted Guests

It’s important to keep your starter loosely covered to prevent “unwanted guests” from entering the container such as flies or particles from the surroundings. If your starter grows mold you should throw it out.

If you’d like to learn more about sourdough starters, see our events page to sign up for a class or send me an email at j_holmes@ncsu.edu.


  1. Calvert, M. D., Madden, A. A., Nichols, L. M., Haddad, N. M., Lahne, J., Dunn, R. R., & McKenney, E. A. (2021). A review of sourdough starters: ecology, practices, and sensory quality with applications for baking and recommendations for future researchPeerJ9, e11389. .11389