If there is one arcane art in baking, it's understanding and using the Baker's Percentage. Once you've grasped the fundamentals, the whole world of baking seems simpler.
At its core, the Baker's Percentage is the ratio of ingredients expressed in a relationship to flour. The first thing to remember is that flour is always 100%. Second, all ingredients are in weights. Third, all ingredients other than flour are expressed as a percentage of flour. Confused yet?
Let's take a look at a simple lean bread dough, the one in Michael Ruhlman's Ratio: The Simple Codes Behind the Craft of Everyday Cooking: flour, 20 ounces; water, 12 ounces; salt, 2 teaspoons; yeast, 1 teaspoon. Simple enough. Now the same dough recipe as a Baker's Percentage.
Lean Bread Dough
For the sake of illustration, let's assume you want to make a bit of bread but when you check you only have 100 grams of flour. If you're looking at a recipe that calls for 20 ounces, good luck with the math. But if you know the Bakers' Percentage, you're ready to roll: flour, 100 grams; water, 60 grams; salt, 3 grams; yeast, 2 grams. Need about 10 pounds of bread? That's a lot of bread, but start with 4 kilos of flour, or 4000 grams, and the rest is simple math: 60% of 4000 = 2400; 3% 0f 4000 = 120; 2% of 4000 = 80.
Why would you care? Because you can play around with your ingredients to make what you want. Say you want some nice extra virgin olive oil in that bread. Water is 60%, so if your liquid equals 60% the recipe will still work. if you use 55% water and 5% olive oil you'll still have 60%, but the bread's character and flavor will change quite a bit. Maybe you find that the lean dough is too dry for you. Okay, increase the water to 65% or even as much as 70%. You'll have some other challenges at 70%; however, hydration at 65% won't change any techniques, but will give better flavor in a cold fermentation (that's when you let it rise in the refrigerator overnight).
Want to add some whole grains to your bread? You can substitute up to 20% of the flour with whole grains and still have enough gluten to make good bread. If you use more than one flour or flour substitute, the total of all the flours' weights will be 100%. So if I used 16 ounces (80%) of unbleached flour, 2 ounces (10%) of white whole wheat flour, 1 ounce (5%) of oat flour, and 1 ounce (5%) of 10-grain cereal, the total would be 20 ounces, or 100%.
I'll give a couple of simple recipes Friday to illustrate.