I’ve been baking sourdough bread for a long, long time; in fact it was probably the first fermented food that I really learned how to make awesomely. A big part of being able to make it so well was learning how to use the “baker’s percentage”.
Flour is a very hard thing to measure, mainly because it can be packed down or loose and fluffy. A cup of packed flour will contain more than a cup of loose flour, and this can mess with your results. For this reason, professionals choose to measure flour by weight, and if you want consistency in your bread, you should too.
And since the bread is being measured by weight, why not measure everything else that way, too? A simple sourdough bread only contains three ingredients: flour, water, and salt, and all can be easily measured by weight.
A bread recipe can be defined using the baker’s percentage. Now, this is not a true percentage, but measures everything relative to the amount of flour. For example, sourdough starters are usually kept at 100% hydration. This means for every 100 g of flour, there is also 100 g of water. [The math is this: (100 g water / 100 g flour) * 100% = 100%.]
Typically, bread dough is made at hydration levels of 60-75%. A typical 65% hydration bread will contain 65 g of water for every 100 g of flour. Figuring out how to make 1 kilo loaf of bread at 65% hydration is not simple math, however. Well, it’s not calculus, but it’s not 3rd grade math, either. There’s a spreadsheet available for members, but here’s the basics of how to do it:
Figure out the ingredient ratios. For a 65% hydration dough, you will use 100 parts of flour and 65 parts of water. That means there are 165 total parts in your dough (we’ll ignore the salt right now). 1 kilogram is 1000 grams, so divide 1000 by 165 to see how much each “part” is worth: 1000/165 = 6.06 g
Now multiply the 6.06 g by how many parts of each ingredient:
Flour: 100 x 6.06 g = 606 g of flour
Water: 65 x 6.06 g = 394 g of water
Salt (at 2%) 2 x 6.06 = 12 g of salt
Figure out how much starter to use. Remember, your starter has flour and water, too, and we need to take that into account. I keep my starters at 100% hydration (equal weights flour and water, as above) The amount of starter you use can vary; on cold days, you can make your bread up to 40% starter; on warm days as little as 25%. For a typical 30% starter in that 1 kg bread from part 1, here is what I would do: 1000 g x .30 = 300 g
That means we need 300 g of active starter for our bread. If your starter is at 100% hydration (a very convenient percentage), this means that half of the starter is flour and half is water. In this case, your 300 g of starter contains 150 g of flour and 150 g of water.
Figure out how much more flour and water you need. Using our numbers from parts 1 and 2:
Flour: 606 g – 150 g = 456 g of flour
Water: 394 g – 150 g = 244 g of water
You can certainly round these to the nearest easily-measured amount if you wish.
That’s it! The simplest way to do it is to add all the ingredients into a bowl and mix it all up. Some people wait to add the salt until the bread has been partially kneaded, but it’s not that critical. If you are making bread at hydration levels at 70% or higher, you may want to hold some water in reserve until the bread is well kneaded, and then add the rest of the water then. The dough will take it up.