Approximately 6 years ago, I attempted for the first time to grow from scratch my own sourdough starter culture. One day in Autumn/Winter time I mixed flour with water, and then I had to wait several days for the mixture to be conquered by millions cells of wild yeast and bacteria, with enough power to inflate a bread dough, which subsequently would bake and transform into bread with great flavour and character. If I was successful, I could use the culture as the mother dough for all my future breads.
I remembered that my very first attempt failed, simply the content in the jar showed no signs of life and activity, no bubbles, no strange smells. Probably the conditions were not appropriate. Maybe, my kitchen was simply not warm enough and/or I did not have the patient to wait and let nature do its job. At that time, I did not have also the knowledge of what exactly I was trying to do. Nevertheless, the second time, just a few days after the first, was crowned with success and since then I am still maintaining and using the same culture, I am giving it to others who ask for it, and of course to my students when coming to my bread courses motivated to start their own sourdough bread adventure.
No matter if you get the starter culture from someone else, I think it is still worth it at some point to try to make it from scratch on your own so as to live this great experience, observing each day how a simple flour and water mixture develops its structure and aroma characteristics.
Establishing a sourdough culture is a simple task to carry out, however, its success is not guaranteed because the process at the microscopic, biochemical level can be very complicated, depending on many factors. The moment when flour comes in contact with water starts a plethora of reactions, in simple words a ruthless war between numerous species of microbes that until then were lying dormant onto the flour particles or into the surrounding environment. Those small creatures will fight hard to dominate by feeding on the flour nutrients so as to build their own empire, protected from intruders.
What has to be decided during this war is whether a subset of beneficial, regarding their health and bread-making properties, microbes will make it till the end prevailing and creating a symbiotic ecosystem, a kind of communal society where each kind of species works in conjunction with the others. Only then an active sourdough culture will be formed and can function as the mother dough for all the breads someone will ever make. Fortunately, in most cases, mother nature takes charge and helps the establishment of such an ecosystem.
After all the years of making sourdough bread, I felt to experience once more this process. So, I sought to give it a try and make a new sourdough culture from scratch.
To do so, I had to prepare the flour and water mixture, close it into a jar, let it on the kitchen counter, refreshing it every day, and observe day-by-day how it reacts. By my side, I had a thermometer to monitor the room temperature, a pH paper to measure how acidity evolves, and a rubber band around the jar to check how much the mixture grows in volume.
So, let the trip begin!
Day 0 denotes the moment when the same by weight amounts of flour and water were mixed and closed into the jar.
After one day, the mixture showed no signs of activity whatsoever. That was expected, it was too early and the room temperature, because of the cold weather outside, was not high enough to initiate rapid microbial growth.
However, already in day 2 signs of life appeared in the jar. The mixture had almost doubled in size and the pH has dropped from neutral values (6-7) to slight acidic ones, around 5. The pH drop indicated the presence of acids, which are metabolic products of lactic- and acetic acid- bacteria (LAB and AAB respectively). Those types of bacteria are known to be among the most numerous species in a sourdough culture. Bacteria are generally more robust than yeasts and can grow under a bigger range of conditions. Keep in mind that at the end of the trip, a mature sourdough culture will have 100 times more bacteria than yeast cells.
Bacteria can feed on the complex carbohydrates (starch and fibers) that are present in the raw flour, while yeasts and unwanted microbes (molds) can metabolise only simple sugars, which are initially not present.
The volume growth indicated the production of gases. Some of them, produced mainly from yeasts like carbon dioxide (CO2), are odourless, while others produced from bacteria contribute to unpleasant smells, something that is usually observed during the first days of the culture evolution. In my case, I could feel already some strange smells, and judging also from the quality of the gas bubbles (were small and for sure not indicative of a mature culture with enough yeast power to inflate a bread dough), I concluded that what I was seeing at that point was mainly bacterial activity.
Suddenly, the next couple of days the mixture remained inactive. I could still smell a blend of pleasant and unpleasant aromas but there was no much gas and volume growth. However, the pH was still dropping to approximately a value of 4-5. I was imagining those moments as a kind of cruel, invisible to the human eye war between microbes.
The beneficial bacteria by having acidified already the environment had killed bad siblings and other microbes that cannot survive under those conditions. At the same time, they had produced food for yeasts. They did so by digesting complex carbohydrate molecules to simple sugars like glucose, fructose, and maltose.
The question that remained to be answered was whether they were still yeasts coping with the sourness of the environment that can feed on those simple sugars and start giving out some alcohol, but most important for bread-making, large amounts of CO2.
That became evident from day 6 and on when the growth in the volume of the mixture was more pronounced and the air pockets on the jar walls were relatively large. That indicated indeed that yeasts survived the acidic conditions and they could now feed on the simple sugars produced by bacteria, producing in turn a lot of CO2.
At the same time, I could also smell the alcoholic content in the jar that was becoming stronger as the culture was reaching a full day without fresh flour.
That pattern kept constant for 3-4 days in a row with the culture growing more and more each day. The pH had dropped more and remained all these days to values between 3.5-4, that is a prerequisite for a mature sourdough culture.
All those facts were speaking for an establishment of a symbiotic culture of wild yeasts and bacteria, simply known as sourdough.
The winner microbes will live happily into this mixture as long as I will provide them from time-to-time with fresh food. In exchange, I will benefit from their metabolic products to make great breads for as long as I want for the rest of my life!
Making a Sourdough starter from scratch
- The establishment of a mature sourdough is highly dependent on the environmental conditions, which will determine how fast the culture will reach its mature state and the exact species of wild yeast and bacteria that will grow and prevail into the flour-and-water mixture. In the current example, the culture was established at a room temperature of 22ºC and at a relative humidity of 30-50%.
- The only components that are needed are flour and water. These are enough for the beneficial microbes to thrive. They do not need any extras, like sugar, juices, fruits, etc.
- In theory, all flours could work. However, it is advised not to use flours that contain additives and to use solely or as part in a mix a whole grain flour. The latter contains many minerals and vitamins that can provide essential nutrients to the microbes and make them happier. Whole grain rye flour for instance is a perfect food source for the microbes, which are growing particularly fast when being fed with it.
flour (here I used a 50-50 mix of whole grain rye flour and white wheat flour (type 550 in Germany))
- Mix well the same amount (in weight) of flour and water until the flour is fully hydrated. Transfer the mixture into a glass jar, close the lid, put a rubber band around it to observe growth, and let it on the kitchen counter.
(You do not need to use large amounts of flour/water because every day a part of the mixture will be discarded and at the end of the process just a small quantity of mature sourdough is enough to grow huge amounts of it in the future. Fill the jar to not more than one-third of its capacity to avoid having the mixture spilling out in case it grows a lot. In this example, I used 25 gr of total flour and 25 gr of water)
- After 24 hours discard two-thirds of the mixture and mix the remaining one-third with the same amounts of fresh flour and water to reach again the same final weight. Here, I used 17 gr mixture + 17gr fresh flour mix + 17 gr water.
(Do this in a small bowl/plate and place the new mixture in the same glass jar that you have cleaned before. Putting the mixture every time into a clean jar helps to avoid having dough pieces sticking on the jar walls that prevent you from observing clearly how the mixture grows)
- Do the same refreshing process every day and observe how the mixture evolves in terms of smells and volume growth. During the early days, you might experience unpleasant smells and no growth. Do not stop, just go ahead with the daily feeding.
- You can stop with the daily feeding process only after the culture has matured and activated. This is evident when after a new feeding it grows substantially (at least double-in-size) after 5-10 hours, depending on the exact room temperature, and for several consecutive days. It should also smell pleasant, something between yogurt, beer, and honey.
(In the last days it might grow faster, reaching a peak and then deflating, losing its volume. This is normal because there was too much gas produced and the mixture does not have enough strength to keep it inside. It is not mandatory but in this case, you can feed your culture twice a day or use a bigger ratio of fresh flour-and-water to the old mixture)
- When you feel that the culture is mature and active, go ahead making some bread or store it in the fridge and feed it as before once every week.