How to get back the sourness your starter lost.
I have been trying for years to find what happens with the sourness of starters. I am referring to the problem of having a starter producing sour bread and after a few weeks or months you lose sourness although the bread rises as it used to. The fact that the bread rises proves that the starter was not neglected.
I have heard many explanations (mainly about change of region) and many suggestions to fix the problem (mainly based on rye) that never worked, at least for me. I faced this problem with SF starters I bought from different vendors and also with my local starter, which I started from scratch. The latter proves that the problem does not have to be in the change of region, but it may have to do with the flour or water used, or method of feeding. My local starter lost its ability to produce sour bread after 4 months. But the bread rises very nicely!
Since I can not find a solution on the internet, I publish a solution here for lovers of sour to enjoy!
I tried to experiment on the subject essentially without a recipe or known path to follow. My friend Spyros Paramithiotis, a research scientist on sourdough in the Agricultural University of Athens (with scientific publications on the subject of sourdough) helped me a lot with his knowledge although he could not help me fix the sourness problem (I had discussed it with him many times). But he gave me crucial information answering different questions over the last 3 years. When he recently gave me the third one I knew I could solve the problem. Here is the crucial knowledge:
1. The bacteria that produce acetic and lactic acids do not really move in the dough! They consume whatever sugars the find nearby. On the other side, yeasts that produce CO_2 to rise the dough, they move. If they consume their nearby food, then they start moving in order to find new sources of food.
2. The acid producing bacteria reproduce at double the rate the yeasts reproduce. So, starting with the *smallest* amount of starter will lead to bigger sourness.
Because of 1. the acid producing bacteria will multiply better if there is plenty of food in the dough. We have to care for them, since they do not move. Do not bother with yeasts, they move and they will find their food. So we need a "sweeter" flour:
3. The flour that has more food for the acid producing bacteria is durum flour. It is the yellow hard flour that is mainly used for pasta so it should be easy to find. In Greece it is widely available. Durum, although hard, it can not rise well (its gluten is not of good quality, and this is why it is not used in bread making).
So if your starter rises well but has recently lost its sourness take it out of the fridge and make a firm dough adding water and durum flour. Put it in a plastic bowl, cover it with plastic wrap and let it on the kitchen counter for 48 hours in warm climates, 72 hours in colder ones. Twice a day punch down with a spoon. Not with your hands as it gets very very sticky. The dough being firm and the flour being from durum wheat will have enough food to sustain life. Repeat once more and after the new 48 or 72 hours you are ready to bake a sour bread. After you used the starter put the remainder back in the fridge. It will be OK for about 2 weeks. Meanwhile you may take small quantities and bake bread. At the end of 2 weeks feed it with durum, leave it out to ferment for 48 or 72 hours and return to the fridge for another 2 weeks.
(Times may have to change depending on temperature.)
To take advantage of information 2. above, use only a teaspoon of starter for 1.4 Kg or 3 lbs of (bread or other) flour. Make the dough in one step (straight dough method), cover and let it ferment for about 22 hours. If the temperature is about 20 C, it will take more than 14 hours to see it rising. But sourness will be better at the end. After 22 hours at 20 C, form loaves and after they rise bake at 230 C.
If your starter has lost its sourness for a long time, you may try again, but one can not know what will happen.
This has worked beautifully for me, when other methods (using rye) have failed. So some people may find it useful.