The below post brought to my attention that fact that not all my readers out there might know what baker’s percentages are, nor what a term like “hydration” means when talking about a bread dough. To answer the easiest part first, “hydration” simply refers to how much water a bread dough contains. As for the percentage, i.e., what a baker means when he/she says a dough has “70% hydration”, that has to do with a slightly odd but very easy system for describing proportions, known as “baker’s percentages”.
Clearly, when a baker says his dough has a hydration of 75%, it doesn’t mean that the dough is 75% water. That would be flour soup…or something akin to a crêpe batter. Rather, what the baker means is that for every measure of flour that’s gone into the dough, 75% of that weight has subsequently been added in water. So if a bread recipe calls for sixteen ounces of flour and has a hydration of 75%, you’d add 12 ounces of water. Simple. Far from being 75% water, the actual dough would be composed of just over 43% water.
It’s a strange sounding system, since it doesn’t really make any mathematical sense. It simply makes flour the yardstick by which all the other ingredients in the recipe are measured. A Jewish challah recipe, for example, is around 50% hydration, 25% eggs, 5% oil, 5% sugar, 1% salt and 1% yeast. What does it mean? It means for every pound of flour you’ll put in half a pound of water, a quarter pound of eggs, about an ounce and a half each of oil and sugar and so on. The total “percentage”, were you to add all those numbers up, is meaningless. 50% + 25% + 5% + 5% + 1% + 1% = 87%. Of what? Who knows? It’s not important.
The important thing is that baker’s percentages provide a simple language of measurement — one that transcends all others: metric, English, Swahili, you name it — by which bakers can scale recipes up or down infinitely. For the neat thing about baking is that the same set of proportions that works for a 2-loaf batch will work for a 20-loaf batch, a 200 or a 2000. In contrast to cooking, baking is a relatively precise science, one which very much appeals to an uptight personality like my own.