Excerpt from Jeffery Hamelman's book: BREAD, A Baker's Book of Techniques and Recipes , page 200m 2004 Wiley & Sons, ISBN 0-471-16857-2:

The Detmolder Method of Rye Bread Production

The Detmolder method of making sourdough rye bread, developed in Germany, is a fascinating and highly effective technique that represents the highest expression of baker's skill. It develops the latent potential of a mature rye culture through a series of builds before the mixing of the final dough. Rye sourdough cultures possess three distinct characteristics - yeast, acetic acid, and lactic acid - and each aspect thrives under different conditions of moistness (hydration), temperature, and duration of ripening. In the Detmolder system, the sourdough is built up in three phases, each favoring the development of one aspect of the sourdough. Paying careful attention to the time and temperature requirements of each phase is necessary in order to obtain the highest-quality results.

The first, or "freshening", phase encourages the development of the yeast cells of the sourdough. The yeast microorganisms present in sourdough thrive under moist conditions at an average temperature, and these conditions are supplied with a high-hydration paste (150 percent hydration) that matures for 5 to 6 hours at about 78 F.

Once the yeast phase has been properly developed, more rye flour and water are added to it. This second build is called the "basic sour" phase. Proper development requires a rather stiff-textured phase (60 to 65 percent hydration) that ripens in comparatively cool conditions for 15 to 24 hours. This phase develops the acetic acid potential of the culture, which eventually imparts the sour tang associated with sourdough bread.

After full ripening of the basic sour, more rye flour and water are added to make the "full sour". This phase develops the lactic acid, which will provide a smooth and mild acidity to the finished bread. Lactic acid development is favored by moist and warm conditions, and in this phase we have mixed a paste of 100 percent hydration and a ripening temperature of about 85 F. Note that ripening is accomplished in a relatively short period of time, 3 to 4 hours. Once the lactic development is complete, the full potential of the sourdough has been developed, and the final dough is ready to mix. Before mixing together the ingredients of the final dough, the baker removes a portion of the ripe sourdough in order to perpetuate the culture.

The building process began with less than 50 grams of culture more than 24 hours earlier, and has been expanded to produce a final dough of more than 18 kilograms. That represents an expansion factor of 360, and the finished loafs are indeed a testament to the wonder of nature, the health of the culture, and - not least - the expertise of the baker.

The precision required for the three-phase method is unlike anything else in bread production. It is also very labor-intensive, and other Detmolder methods simplify the process: For example, there is one-phase method, as well as a two-phase. Although these breads don't have quite the ultimate flavor complexity of breads made with the three-phase technique, they are of excellent quality and fit more easily into many production schedules.