Outlook for Modern Large Scale Wheat Sourdough Production

The concept for a plant capable of manufacturing liquid sponges developed by the Reimelt company constitutes a new approach to the development of large wheat sourdough plants. Reimelt has developed a plant for the fermentation of liquid sponge, which constitutes a technical breakthrough in sponge production. The capacity of the liquid sponge plant is 2000 kg/hr at a fermentation time of 4 hr. The plant is operated with wheat flours with a high gluten content (wet gluten >30%) and pronounced viscoelastic properties.

The plant consists essentially of a system of mixing flour, water, and yeast, two fermentation tanks operated in tandem, a plate cooler, and an insulated storage tank fitted with a stirrer. There are no stirrers in the fermentation tanks, which are filled from above and emptied from below. The principle of first-in first-out as applied in fermentation tubes has thus been adopted here, too. The same principle was also applied to the continuous Reimelt rye sourdough fermentation tank, except that the tank is filled in a continuous flow from its base to its top. This mode of operation was not feasible for liquid sponge fermenters designed without a stirrer as the fermentation tanks act as ripening tanks in a batchwise mode of operation.

The ripened liquid sponge is pumped through the outlet in the base of the tank and over the plate heat exchanger into the storage tank. Owing to the stable gluten network, which is interspersed with gas and determined by the flour characteristics, no mixing of the individual layers of dough occurs over the height of the fermentation tank. Therefore, the tank is emptied in a plug flow pattern. In respect of the flour characteristics, the critical density of the liquid sponge must not exceed a value of 0.65 g/cm3. The critical density of the fermenting sponge can only be limited by means of the quantity and dough-raising power of the yeast used, as it is not possible to cool or stir the fermentation tank.

Such sponges develop an acidity of around 5 mL TTA mainly owing to the formation of acetate by the yeasts. The acidity could only be increased within the fermentation time of 4 hr if an inoculum of lactic acid bacteria were added to the sponge. However, this possibility is still in an experimental stage. It is for this reason that the problem of how to design large-scale plants for semicontinuous or continuous wheat sourdough cannot yet be considered to have been totally solved.

In the context of such developments in processing technology, it should be noted here that, in accordance with the definition laid down by Olms (47) (Fig. 13), an acidity of 7 mL TTA constitutes the boundary between the two types of preliminary dough. The rheological and microbiological requirements as well as the requirements for processing technology need to be fulfilled in order to resolve the problem deriving from that definition. The microbiological requirements consist first and foremost in selecting microorganisms (lactic acid bacteria and yeasts) that form a large number of precursors of flavor components but few organic acids (lactic acid and acetic acid) and carbon dioxide in a short fermentation

Figure 13 Distinction between sponge and wheat sourdough.

time. The formation of lactic acid is particularly important as it can destabilize the gluten network.

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