Files and recipes fill my folders. Many come from classes taken years ago, notes and half ledgible percentages marked on fading papers. The other day deciding what to bake, I sorted through some of these scribblings, coming upon a print-out from an email correspondence with my former bread baking instructor, David Norman. In it, he gave me advice on how to convert hydration in preferments, biga to levains.
His example was this:
10Kg. Flour as total
Biga would be 4kg flour
2.6 liters water (65%)
Final Dough 4.4liters water,(total water is 7 liters or 70%, but the final dough water is 4.4 liters, meaning 7liters -2.6 liters in Biga.
Now to convert to another hydration preferment you would keep the total water and flour the same.
10 kg flour total
New biga: 4 kg flour
5 liters water (125%)
Final dough: 6Kg flour
Anyway, if you're going to switch from a yeasted preferment like a biga or poolish to a sourdough, you will want less of the flour in the preferment. In the example above, 40% of the flour is in the preferment. This is normal for Italian style biga breads. However, 40% would be too much if it were a sourdough. The acid would make the dough harder to develop and the taste too sour. If you wanted a bread that was not sour, reduce the flour to 5-10%. Form more sourdough flavor, use 15-20%.
It was an easy lesson then, as it is now. But typically (for me) I decided to go against his lesson – don't students ever learn?
Wouldn't you know, I payed no attention and stuck with the 40%, and I used all sorts of different flours, spelt, rye, whole wheat, white wheat, in various proportions. So far the dough did'nt seem to have problems with development, so I wonder if different flours make the higher amount of sourdough react differently?
The test will be in the taste of the finished loaf I guess, without having retarded the loaf, it's got a wonderful wheaten smell, mild and no notes of acidity.
Sliced it tasted absolutely marvelous, a crisp dough without being overly tough, and some acidic tones but quite flavorful and nuances from the various flours make for a fairly airy crumb.