The basis of every sourdough process is the optimum coordination of the raw material and processing parameters described in the following text in regard to the desired sourdough quality. None of the parameters listed has an effect on its own, there are numerous interactions between the individual factors which have to be taken into consideration.
A perfect starter is the prerequisite for the success of the sourdough process. The starter contains the desired microflora which is activated and reproduced in the single sourdough stages. The composition of the bacterial culture of the starter influences the type and the quantity of the fermentation products formed in the sourdough.
Common practice is to take the starter from the mature sourdough and to renew this regularly by means of a pure culture sour. A pure culture sour is understood to be a starter with an exactly defined composition of lactic acid bacteria and sourdough yeasts. The use of a spontaneous sourdough as a starter, which could frequently be seen in previous times, is practically no longer realized for reasons of poor reproducibility.
To avoid foreign fermentations, it is important to introduce a sufficient quantity of lactic acid bacteria via the starter. A too large quantity of starter lowers the initial pH value too strongly, so that the desired enzymatic decomposition procedures of the flour ingredients of the sourdough are reduced. The quantity of starter has therefore to be adjusted to the temperatures, standing times and dough firmness of the single stages. Short sourdough processes require a higher quantity of starter than long sourdough processes.
The temperature is one of the most important influencing variables of sourdough fermentation. It is mainly based on the micro-organisms used. Temperatures of 30° C and above mainly benefit the homo-fermentative lactic acid bacteria which only form lactic acid. Processing of this very warm sourdough leads to a mild to insipid bread aroma.
In the case of sourdoughs with cool processing, this means temperatures of 22 – 25° C, predominantly hetero-fermentative lactic acid bacteria reproduce which, in addition to lactic acid, also form acetic acid. Due to the higher contents of acetic acid, these sourdoughs give a strong bread taste. Attention has also to be paid to the influence of the temperature on the speed of acidification.
Too low temperatures slow down the metabolic activity of the micro-organisms, so that less acid is formed and the sourdoughs are still too young after the normal maturing time. Vice versa, the speed of the acidification can be increased by raising the temperature.
The more the micro-organisms should reproduce in a sour stage or the more acid should be formed, the longer the maturing times have to be. To avoid mis-fermentations or too young sourdoughs, it is essential to observe the prescribed maturing times of the relevant stages.
The longer the maturing time of the single sourdough stages selected, the more intensely the flour ingredients swell and the better the freshkeeping of the baked goods. In turn, the maturing times also influence the quantity of starter, the temperature and the dough firmness. The optimum maturing time can be ascertained by means of sensory assessment of the single stages, but also by the determination of the degree of acidity and pH value.
Dark rye flours and coarse rye with a high degree of extraction are rich in enzymes, vitamins, minerals and fermentable carbohydrates, as well as proteins. They provide good prerequisites for sourdough fermentations and acidify better than lighter-coloured rye flours with lower mineral contents and poorer enzyme activity. Should the mineral content be too high, then a tart and sour to bitter aftertaste can be the result.
Over and above the enzyme activity and the availability of flour ingredients which can be fermented, the buffering capability of the flours to be acidified plays an important role. The higher the mineral content of the flours, the better the pH value is buffered. The buffering capability of a flour can be recognized by how fast the pH value of the sourdough falls during fermentation. Is it high, then the pH value drops relatively slowly, so that high degrees of acidity are achieved. In the case of flours with poor buffering properties, the pH value falls relatively quickly, often meaning low degrees of acidity.
With flours of a higher type number (e.g. rye flour type 1370), higher degrees of acidity can be achieved than with flours of a low type number (e.g. rye flour type 815) when using the same parameters.
A higher dough yield promotes the enzymology inherent to the flour more strongly than a lower one. At the same time, soft sourdoughs increase the activity of the micro-organisms, so that the acidification is intensified and the speed of the acidification increased. In firm sourdoughs, the activity of the sourdough microflora is slowed, leading to a greater tolerance regarding the point of maturity of the sourdough and to an intensification of the development of aroma (formation of acetic acid). Should the acidification be carried out under relatively warm and soft conditions (dough yield 190 – 220), mainly lactic acid is formed, which gives a relatively mild bread taste. A strongly aromatic bread taste can be achieved by means of cool and firm sourdough methods (dough yield 160 – 170).