A problem often faced by sourdough bread bakers is what to do with all of the excess starter resulting from the necessary feedings. Waste can be minimized by using up all but a tablespoon or two of starter when baking, and keeping your starter in the refrigerator between bakes. Even so, it still needs to be fed. If you don't bake for a while, quite a bit can accumulate. And, even if you use a scale, growing an exact amount of starter is inconvenient.
A simple solution is to use the excess starter in your bread, reducing the amount of flour and water to compensate. It turns out that the amount of starter used is not critical. I have found recipes on the Internet that call for from 20% to 155% starter (by weight, with respect to the flour.) This handy calculator may be used to easily adjust your recipe to use up your starter. Instructions are below the calculator.
This calculator may also be used to adjust recipe sizes, dough hydration, and do many other bread-related calculations. See below.
Instructions
Adjust recipe to use a specified amount of starter: Enter the final desired dough weight and hydration percentage in the above form.
If you have a scale: Weigh the starter you want to use and enter its weight. Click Calculate. The amount of flour and water are shown. Adjust dough consistency if necessary by adding a little extra water or flour. The weights given will be very close, but allowances must be made for moisture content of your flour. Don't forget the salt!
If you don't have a scale: Stir the gas out of the starter that you want to use, and measure it using measuring cups. Enter the number of cups you have here (use decimal numbers for fractional cups): Starter Weight is required and must be numeric Add the amount of water shown. To measure flour, just scoop out of the bag and level. The amount of flour shown is approximate. Mix in flour until the desired dough consistency is achieved. Don't forget the salt!
Recipe Analyzer: Used to find the final dough weight (less salt) and hydration percentage from an existing recipe. Enter the weight and percentage hydration of the starter in the form above. Enter the grams of flour and water the recipe calls for here: Flour: Water: Flour is required and must be numeric Water is required and must be numeric
Scale a recipe: Increase or decrease the size of the recipe shown in the calculator. Enter the percentage here: Percentage is required and must be numeric Or new total dough weight: New total weight is required and must be numeric
Calculate how much starter you need to get a specified percentage of flour from the starter: For example, you are making whole wheat bread out of white flour starter, and want 60% white flour and 40% whole wheat in the final loaf. Fill out the Total Dough Weight and percentage hydration above. Enter 60 here: Percentage is required and must be numeric
Convert Baker's Percentage: Enter Baker's percentage here: Percentage is required and must be numeric
Notes:
Hover the mouse pointer over the various controls on this calculator for more information.
Salt is based on 2% of total flour weight, and is not included in final dough weight.
Percentages given are bakers' percentages. It is not necessary to understand bakers' percentages to use this calculator, but these figures are provided for those who want them. Used by professional and commercial bakers, and increasingly by hobbyist bakers, is a way of defining a recipe based on weight of ingredients. Flour is always 100%. Other ingredients are based on the weight of the flour. For example, if the Water baker's percentage is 50%, this means that the water added to the mix weighs half as much as the flour. Recipes in Bakers' percentages makes it easier to scale and make it larger or smaller. (However, this calculator makes it even easier. It does all the math for you!)
Hydration percentages are based on the amount of water with respect to flour. So dough with a 70% hydration level has water that weighs 70% of what the flour weighs. It does not mean that the dough is 70% water. Starter is most commonly hydrated to 100%, meaning it has as much water as it has flour by weight. Hydration percentage is expressed in Baker's percentage. Using the Baker's Percentage converter above, we see that dough with 70% hydration actually has 59% flour and 41% water.
This calculator is intended for sourdough bread baking. To use for yeast or quick breads, enter 0 for Starter Weight. It is up to you to figure out how much yeast or baking soda/powder to use.