A very good question was “tweeted” in to me late last week by, well…I don’t know his (or her) name. But it was a darned good question. It went like this:
You are deep into the historical aspect of baking. In the time before artificial refrigeration, how were preferments managed?
I knew I’d like this Twitter business. So what makes this such a good question? It’s good because the questioner clearly has a sense for how unbaked dough behaves when it’s left at room temperature for extended periods of time. It proofs, and it proofs, and it overproofs, and finally after many hours breaks down into a stanky puddle of alcohol-soaked goo. It rots in other words, as the available starch is consumed by increasing populations of yeast and bacteria. Nowadays, we refrigerate our preferments to keep this kind of thing from happening, however it wasn’t that long ago that there was no refrigeration, especially in hot places like bakeries. So what kept the preferments fresh enough to use?
A big part of the answer is scheduling. A thriving city bakery would have produced bread in multiple batches at regular intervals around the clock. Assuming that some dough was reserved from each batch to be added to the next, there wouldn’t have been time for this “old dough” to break down too far before it was incorporated into the next production.
Another part of the answer is the way in which the preferments were formulated. The smaller the amount of yeast added to a preferment, the longer it takes for that preferment to mature. Bakers can also control the rate at which microbes eat and reproduce by, say, adding salt. Methods would have varied markedly from bakery to bakery, for indeed there’s almost no limit to the ingenious techniques humans have devised for manipulating yeast, especially over the last 150 years.