So what does it mean when a baker says a bread’s “hydration” is 80%? Of course it has to do with how much water is in the dough, but what exactly does “80% hydration” mean? It doesn’t mean the recipe is 80% water, since that would make soup. In fact it has to do with what are known as “baker’s percentages”, a slightly odd but very easy way of talking about proportions of ingredients in bread.
Baker’s percentages are all based on weight, since as I’ve written time and time again, volumes simply aren’t reliable in the world of baking. Flour can get packed down, throwing off your recipe. But employing a standard of weight it doesn’t matter how packed down a cup of all-purpose flour gets, since it will always weigh 5 ounces.
So, bakers percentages. The thing that makes the system unique is that it uses the flour in the recipe as the yardstick by which all the other ingredients are measured. So let’s say a bread recipe calls for ten ounces of flour, eight ounces of water, two ounces of butter, two ounces of egg, and a quarter ounce each of yeast and salt. It’s hydration would be 80%, since eight is 80% of ten. Butter and egg content would be 20% each, salt and yeast .25%. That would be one seriously slack dough, but then this is all hypothetical.
Now, you’re probably wondering what kind of percentage system this is where all the ingredients add up to 120.50% (not counting the flour, which is considered an additional 100%). True, it really makes no sense, except that it’s an easy — and highly scalable — way of remembering bread proportions. For however much flour you’re using, you add X percentage of X things to get the bread you want. And since unlike cooking, bakery recipes can be scaled up and down infinitely, the same formula that works for a two-loaf batch will work for a 20-loaf batch, or a fifty, a hundred, whatever. Yeah, so, it’s a percentage system that doesn’t add up to 100%. Big deal. What are we bakers, perfect?